Engine Not Heating to Operating Temp????

[87K5Newbe]

Hello, I have a Ramjet 350 MEFI4 swapped into my K5 by a previous owner.

My engin temp never seems to go above 140-160degrees when ideling or driving around town, or 2 tracks trails when hunting.
(this i a problem because it idles high when cold and if there is a load on the motor with the throttle closed the motor will drive me along the trail and when the clutch is pushed in the motor will rev to like 1500 rpm or higher and takes 15 or more seconds to come to idle again.)

On the highway running 60 to 70mph (FYI 3speed with granny, high axel gears so 70mph is probably over 2500/3000rpm. dont have a tach yet.) she will get right up to 190 ish on the gauge but not go above.

This is what i have done so far.
Fan cluch turns with resistance when cold and you can defiatly hear the fan noise when reving the motor in park or hard acceleration. so i assume that is workin properly.
replaced sending unit located on left head. connected to stock temp gauge in cluster. (ram jet temp sending unit is located on intake maniflold near thermosat housing)
I had a small leak on the lower radiator near the hose so i swapped the radiator to a new nappa radiator for a 350 with the long single core instad of 3 seperate cores.
Changed the thermostat to 180 safety stat. on first start up it locked in the open postion. noticed it was running even cooler than before, which a week or two later i found it and replaced it with a regular napa 180 thermosat.
I have verified motor temp with IR gun near thermostat on intake manifold and engine temp sending unit is 140F when idleing for 20 minutes.

outside temp has been between 70F to 30F. on the colder days interstate speeds she just runs cooler.

STUPID QUESTION: What holds the thermosat down on the intake maniflod. it appears the thermosat hose housing ID is larger than the OD of the thermosat and the gasket is the only thing holding the thermostat down. Thermostat fits nicely into the intake manifold groove.

I have no coolant bypasses on this motor, like some suggest for overheating on the ramjet350. I have the opposite problem.

any help will be appreciated.

 

[Wes Harden]

a computerized car would run a 195° t stat, but your 180° should run 190° at any operating speed. I don't recommenced the 195° stat, unless you still have cats and emissions equipment and testing.

So what changes between the 2 temperatures, rpm. My thinking is the coolant at 70 mph is flowing much faster than the lower speeds, and the rad doesn't have time to cool it.
That is different problem from the running to cool. Need to verify the actual coolant temp vs the ecm signal temp. High resistance in the ecm temp sensor circuit will fool the ecm into thinking the engine is still cold. Check you engine ground, verify the pins in the sensor connector are tight and no corrosion. If you have an infrared temp gauge you can measure the temps at different spots around the cooling system to help trouble shoot.

 

[Wes Harden]

Yes the housing is supposed to keep the t stat in place. If yours is aftermarket it maybe poorly designed.

 

[dyeager535]

Fan shouldn't be running with the engine at a low operating temperature. Quick random check says engine should be at least 170* before the fan clutch locks up.

There are clutched fans without the thermostatic portion (bimetallic spring on the front face) which are not what GM used. I have doubts the fan alone could drive temps that far below thermostat temp, but thats another matter.

Perhaps your thermostat is bypassing fluid if it's raising off its seat?

Only thing I can think of as a way to test is to remove the fan blades and see what happens. I wouldn't drive it far (just far enough to get the temp moving so I didn't have to wait so long) but since the problem is low speed/idle, once it starts to build heat, it SHOULD exceed thermostat temp pretty quickly without a fan. If the thermostat is bypassing, I'm not sure the engine would ever warm up. It would be akin to running without a thermostat, which IME resulted in a perpetually cold engine.

Thermostat temp rating isn't a problem here, as your engine clearly exceeds the ability of the thermostat to control temp, but only under load.

 

[87K5Newbe]

Yes the housing is supposed to keep the t stat in place. If yours is aftermarket it maybe poorly designed.

Thanks. i was thinking the same thing, but was not sure. thanks for the help.

 

[87K5Newbe]

Fan shouldn't be running with the engine at a low operating temperature. Quick random check says engine should be at least 170* before the fan clutch locks up.

There are clutched fans without the thermostatic portion (bimetallic spring on the front face) which are not what GM used. I have doubts the fan alone could drive temps that far below thermostat temp, but thats another matter.

Perhaps your thermostat is bypassing fluid if it's raising off its seat?

Only thing I can think of as a way to test is to remove the fan blades and see what happens. I wouldn't drive it far (just far enough to get the temp moving so I didn't have to wait so long) but since the problem is low speed/idle, once it starts to build heat, it SHOULD exceed thermostat temp pretty quickly without a fan. If the thermostat is bypassing, I'm not sure the engine would ever warm up. It would be akin to running without a thermostat, which IME resulted in a perpetually cold engine.

Thermostat temp rating isn't a problem here, as your engine clearly exceeds the ability of the thermostat to control temp, but only under load.

Thanks for your time. I will give that a try. will also check out getting a new thermostat housing to prove out the thermostat bypass.

 

[87K5Newbe]

a computerized car would run a 195° t stat, but your 180° should run 190° at any operating speed. I don't recommenced the 195° stat, unless you still have cats and emissions equipment and testing.

So what changes between the 2 temperatures, rpm. My thinking is the coolant at 70 mph is flowing much faster than the lower speeds, and the rad doesn't have time to cool it.
That is different problem from the running to cool. Need to verify the actual coolant temp vs the ecm signal temp. High resistance in the ecm temp sensor circuit will fool the ecm into thinking the engine is still cold. Check you engine ground, verify the pins in the sensor connector are tight and no corrosion. If you have an infrared temp gauge you can measure the temps at different spots around the cooling system to help trouble shoot.

First Thank you for your time. I have checked the radiator end caps, thermostat housing with a IR gun and they are low to mid 140's if i rev her for a little she might see 160. checking the head temps with the IR gun near the sending unit gives me quite a range from 170 to 200 depending on how close i am to the exhaust manifolds. I checked other parts of the block and they are 150-169 depending on where and the distance of the gun. cant verify the ecm temp as i dont have an MEFI4 scanner yet. I am going to purchase one in time i was looking at the TechMate Pro from Rinda. but for over $500 bucks most of all parameters are read only from what i have read. thanks again.

 

[blazer74]

Wouldn’t happen to be a fail safe thermostat?

 

[Blue85]

Fan shouldn't be running with the engine at a low operating temperature. Quick random check says engine should be at least 170* before the fan clutch locks up.

I don't think this is worded right. The fan always spins when the engine is running and the clutch is never locked completely tight. It's a varying state of friction based on temperature. Of course, that's not temperature of the engine, but temperature of the air being drawn over the fins on the fan clutch. Far from an ECM-controlled fan that's on/off.

 

[Wes Harden]

you really don't need a scan tool read only at that price point. Innova scan tools will give you live info for a 3rd of that or less depending model chosen

 

[folkenheath]

If the thermostat is working correctly the fan usually cannot cool it down further than that because the thermostat should be shut, at that point the coolant is not supposed to be flowing through the radiator. The fan clutch and thermostat are both mechanical devices, and they don't open instantly. The thermostat will start to open around the rated temp, and it may take many degrees for it to be open all the way depending on the thermostat. It will usually reach an equilibrium where its open just enough to maintain a steady temp somewhere slightly above its rating.

So the problem is likely in your thermostat, which you have changed twice so that would seem to rule it out. One silly but important question, are you sure it's not in upside down? If the PO put it in upside down and you just replaced it the same way I could see that happening. The spring side goes down in the intake.

Your heater core hose doesn't allow the coolant to also flow through the radiator does it?

I have also seen people install those rear coolant hoses in their engine from the back of the intake to the front, and put an adaptor under the thermostat housing to connect the hoses to the front, and then put the thermostat below the adaptor. This essentially cools the block with no thermostat and the heads with a thermostat, not ideal. If someone is running one of those with a thermostat, the thermostat should be on top the adaptor. But usually people running those are in more of a racing environment and aren't running a thermostat, so it was a weird combination.

If the thermostat can fit up inside the housing, then it may not be being held down by the housing and could allow coolant to bypass.

Have you verified your ignition timing is what is is supposed to be? You can download the instructions for the ramjet from here:

Ramjet Manual

This is what it says on timing...

Setting Initial Timing: In order to change base timing on the system, the ECM has to be entered into the "service mode" using the diagnostic trouble code (DTC) tool, part number 12489400. This can be accomplished by attaching the DTC tool to the data link connector on the wiring harness.

1. Turn the engine's ignition switch to the off position (Engine not running)

2. Place the DTC tool's test switch in the off position and plug the tool into the data link connector on the wiring harness.

3. Start the engine, and place the DTC tool test switch in the on position. The IC module will then go to base ignition timing. At this time, the base timing can be adjusted by turning the distributor. Using a timing light, set base timing at 12° Before Top Dead Center (BTDC).

It sounds like you have done a lot to confirm that the gauged is correct, however, it would be nice to see what the ECU sensor says. They usually have their own separate ground in those sensors so they don't ground through the sealed threads, they are typically more reliable. If you don't have a scan tool, get the engine up to temp, unplug the connector and measure the resistance of the two sensor terminals with a multimeter. Then compare it to the chart of what it should be at that temp. Want want to make sure its not something else that is causing the high idle like a simple throttle blade adjustment or something.

Here is a sensor chart...(not necessarily the dash gauge sending unit though). You can verify on your gauge if more or less resistance increases temp by unplugging the sending unit wire, if the gauge reads very cold, then it may have too much resistance through the threads showing a lower temp. The ECU sensor won't have that problem.

 

[dyeager535]

I don't think this is worded right. The fan always spins when the engine is running and the clutch is never locked completely tight. It's a varying state of friction based on temperature. Of course, that's not temperature of the engine, but temperature of the air being drawn over the fins on the fan clutch. Far from an ECM-controlled fan that's on/off.

Correct. However, since the OP mentioned "Fan cluch turns with resistance when cold and you can defiatly hear the fan noise when reving the motor in park or hard acceleration." that leads me to believe the fan is locked up. I never had a problem hearing the clutch fan "kick on" when it was locked up tight.

While I don't feel it's a large factor, you absolutely can "overcool" a motor even with a properly operating thermostat. Coasting downhill you (or at least I) can easily drive temperature well below rated thermostat temp, and that is simply thermal conduction. It's the same reason why some OEM's run electric fans after engine shutdown. The coolant is still capable of conducting heat regardless of liquid flowing/being pushed through the system. Again, I don't think an engine fan in moderate ambient temps at idle is going to make an engine run constantly cool, but I've never tested it. However it will definitely not help an engine get up to temp regardless.

Suppose I could...

 

[87K5Newbe]

If the thermostat is working correctly the fan usually cannot cool it down further than that because the thermostat should be shut, at that point the coolant is not supposed to be flowing through the radiator. The fan clutch and thermostat are both mechanical devices, and they don't open instantly. The thermostat will start to open around the rated temp, and it may take many degrees for it to be open all the way depending on the thermostat. It will usually reach an equilibrium where its open just enough to maintain a steady temp somewhere slightly above its rating.

So the problem is likely in your thermostat, which you have changed twice so that would seem to rule it out. One silly but important question, are you sure it's not in upside down? If the PO put it in upside down and you just replaced it the same way I could see that happening. The spring side goes down in the intake.

Your heater core hose doesn't allow the coolant to also flow through the radiator does it?

I have also seen people install those rear coolant hoses in their engine from the back of the intake to the front, and put an adaptor under the thermostat housing to connect the hoses to the front, and then put the thermostat below the adaptor. This essentially cools the block with no thermostat and the heads with a thermostat, not ideal. If someone is running one of those with a thermostat, the thermostat should be on top the adaptor. But usually people running those are in more of a racing environment and aren't running a thermostat, so it was a weird combination.

If the thermostat can fit up inside the housing, then it may not be being held down by the housing and could allow coolant to bypass.

Have you verified your ignition timing is what is is supposed to be? You can download the instructions for the ramjet from here:

Ramjet Manual

This is what it says on timing...






It sounds like you have done a lot to confirm that the gauged is correct, however, it would be nice to see what the ECU sensor says. They usually have their own separate ground in those sensors so they don't ground through the sealed threads, they are typically more reliable. If you don't have a scan tool, get the engine up to temp, unplug the connector and measure the resistance of the two sensor terminals with a multimeter. Then compare it to the chart of what it should be at that temp. Want want to make sure its not something else that is causing the high idle like a simple throttle blade adjustment or something.

Here is a sensor chart...(not necessarily the dash gauge sending unit though). You can verify on your gauge if more or less resistance increases temp by unplugging the sending unit wire, if the gauge reads very cold, then it may have too much resistance through the threads showing a lower temp. The ECU sensor won't have that problem.

View attachment 460012

Thanks, i will check the resistance of the thermocouple. themostat is in spring down, housing is holding down correctly(i was mistake before on the OD fo the housing).

 

[87K5Newbe]

Wouldn’t happen to be a fail safe thermostat?

not any more i took it out and installd a regular 180° thermostat

 

[87K5Newbe]

If the thermostat is working correctly the fan usually cannot cool it down further than that because the thermostat should be shut, at that point the coolant is not supposed to be flowing through the radiator. The fan clutch and thermostat are both mechanical devices, and they don't open instantly. The thermostat will start to open around the rated temp, and it may take many degrees for it to be open all the way depending on the thermostat. It will usually reach an equilibrium where its open just enough to maintain a steady temp somewhere slightly above its rating.

So the problem is likely in your thermostat, which you have changed twice so that would seem to rule it out. One silly but important question, are you sure it's not in upside down? If the PO put it in upside down and you just replaced it the same way I could see that happening. The spring side goes down in the intake.

Your heater core hose doesn't allow the coolant to also flow through the radiator does it?

I have also seen people install those rear coolant hoses in their engine from the back of the intake to the front, and put an adaptor under the thermostat housing to connect the hoses to the front, and then put the thermostat below the adaptor. This essentially cools the block with no thermostat and the heads with a thermostat, not ideal. If someone is running one of those with a thermostat, the thermostat should be on top the adaptor. But usually people running those are in more of a racing environment and aren't running a thermostat, so it was a weird combination.

If the thermostat can fit up inside the housing, then it may not be being held down by the housing and could allow coolant to bypass.

Have you verified your ignition timing is what is is supposed to be? You can download the instructions for the ramjet from here:

Ramjet Manual

This is what it says on timing...






It sounds like you have done a lot to confirm that the gauged is correct, however, it would be nice to see what the ECU sensor says. They usually have their own separate ground in those sensors so they don't ground through the sealed threads, they are typically more reliable. If you don't have a scan tool, get the engine up to temp, unplug the connector and measure the resistance of the two sensor terminals with a multimeter. Then compare it to the chart of what it should be at that temp. Want want to make sure its not something else that is causing the high idle like a simple throttle blade adjustment or something.

Here is a sensor chart...(not necessarily the dash gauge sending unit though). You can verify on your gauge if more or less resistance increases temp by unplugging the sending unit wire, if the gauge reads very cold, then it may have too much resistance through the threads showing a lower temp. The ECU sensor won't have that problem.

View attachment 460012

also yes.............. the heater is always flowing regardless of either lever postion in the cab. heater is pipped from the passenger front side of the intake to the core out of the core to the upper part of the passenger side of the radiator. i was wonder if that was supposed to stop when on cool and off. i did pinch of the heater supply to the core today and did not see any change while ideling... shoudl have drove it in hindsight.
Ignition timming cannot be checked as i cant find a bracket for timming reference any where around the harmonic ballencer. only the ballencer.

also i did read about load on the engin with the throttle at 0 causing can cause an overspeed issue in one of the ramjet pdf's i have downloaded, just can remember which one. Idle is high when it is cold and so that happens often and it drives me nuts expecailly if i am pulling in the clutch to crawl over a rock or have to stop on a hill and move slowly forward. i have had a few time when i was working it pretty hard and had to pull in the clutch and the idle droped right down like a normal motor, looked down and temp was warmer than normal (my current normal :P).... I have a tach coming and it will be here tomorrow.

 

[dyeager535]

Decent writeup, I was specifically looking for the timing tab. Only one image would seem to be likely to have it visible, yet I dont see it. No idea what the Ramjets used for timing tabs.

BillaVista.com-MEFI-4 Fuel Injection Tech Article by BillaVista

www.billavista.com

More, apparently timing tabs are not a thing on Ramjets.

Timing for 350 RamJet

I am attempting to set the timing @ the required 10 degrees BTDC but there are no marks on the balancer. There is only one V notch on the chain cover and one heavy mark on the balancer, normally this is the TDC position. Anyone else have this problem and if so what did you do to set the initial...

www.camaros.net

Ramjet 350 Timing Question

I need to check the timing on my ramjet 350 but there is no timing tab on the block and as far as I can tell from searching this is how the engine comes. I have the tool to set the base timing but the manual says to adjust it to 10* BTDC using a timing light. How in the heck to you find 10* BTDC...

www.pirate4x4.com

 

[Wes Harden]

still thinking the ecm temp sender is giving incorrect reading, at normal coolant temps. Since your infrared checks 180° plus at gauge temp sender, when your idle is correct I bet your on the verge of over heating. Have the grounds been checked ?

 

[87K5Newbe]

If the thermostat is working correctly the fan usually cannot cool it down further than that because the thermostat should be shut, at that point the coolant is not supposed to be flowing through the radiator. The fan clutch and thermostat are both mechanical devices, and they don't open instantly. The thermostat will start to open around the rated temp, and it may take many degrees for it to be open all the way depending on the thermostat. It will usually reach an equilibrium where its open just enough to maintain a steady temp somewhere slightly above its rating.

So the problem is likely in your thermostat, which you have changed twice so that would seem to rule it out. One silly but important question, are you sure it's not in upside down? If the PO put it in upside down and you just replaced it the same way I could see that happening. The spring side goes down in the intake.

Your heater core hose doesn't allow the coolant to also flow through the radiator does it?

I have also seen people install those rear coolant hoses in their engine from the back of the intake to the front, and put an adaptor under the thermostat housing to connect the hoses to the front, and then put the thermostat below the adaptor. This essentially cools the block with no thermostat and the heads with a thermostat, not ideal. If someone is running one of those with a thermostat, the thermostat should be on top the adaptor. But usually people running those are in more of a racing environment and aren't running a thermostat, so it was a weird combination.

If the thermostat can fit up inside the housing, then it may not be being held down by the housing and could allow coolant to bypass.

Have you verified your ignition timing is what is is supposed to be? You can download the instructions for the ramjet from here:

Ramjet Manual

This is what it says on timing...






It sounds like you have done a lot to confirm that the gauged is correct, however, it would be nice to see what the ECU sensor says. They usually have their own separate ground in those sensors so they don't ground through the sealed threads, they are typically more reliable. If you don't have a scan tool, get the engine up to temp, unplug the connector and measure the resistance of the two sensor terminals with a multimeter. Then compare it to the chart of what it should be at that temp. Want want to make sure its not something else that is causing the high idle like a simple throttle blade adjustment or something.

Here is a sensor chart...(not necessarily the dash gauge sending unit though). You can verify on your gauge if more or less resistance increases temp by unplugging the sending unit wire, if the gauge reads very cold, then it may have too much resistance through the threads showing a lower temp. The ECU sensor won't have that problem.

View attachment 460012

Used an IR Gun. Factory thermocouple 77F = 2198Ω to block 2199Ω to brass. Ramjet thermocouple 75F = 2459Ω.. i tried to use inderect proportion math to figure the 75f, but this table doesnt jive with inverse or direct proportion if i plug the values in as they are on the chart. you would think the resitance would be inversly proportional to the temperature. Either way both thermocouples are not close to this chart.

 

[folkenheath]

Used an IR Gun. Factory thermocouple 77F = 2198Ω to block 2199Ω to brass. Ramjet thermocouple 75F = 2459Ω.. i tried to use inderect proportion math to figure the 75f, but this table doesnt jive with inverse or direct proportion if i plug the values in as they are on the chart. you would think the resitance would be inversly proportional to the temperature. Either way both thermocouples are not close to this chart.

What was the engine temp when you measured the sensor resistance?

I don't expect the gauge sending unit to be that chart, only the EFI sensor, but it could also be a different sensor and that chart is wrong. I bet if you search the sensor part number you can find a resistance chart for it, though many GM temp sensors are the same values, not all.

also yes.............. the heater is always flowing regardless of either lever postion in the cab. heater is pipped from the passenger front side of the intake to the core out of the core to the upper part of the passenger side of the radiator. i was wonder if that was supposed to stop when on cool and off. i did pinch of the heater supply to the core today and did not see any change while ideling... shoudl have drove it in hindsight.
Ignition timming cannot be checked as i cant find a bracket for timming reference any where around the harmonic ballencer. only the ballencer.

also i did read about load on the engin with the throttle at 0 causing can cause an overspeed issue in one of the ramjet pdf's i have downloaded, just can remember which one. Idle is high when it is cold and so that happens often and it drives me nuts expecailly if i am pulling in the clutch to crawl over a rock or have to stop on a hill and move slowly forward. i have had a few time when i was working it pretty hard and had to pull in the clutch and the idle droped right down like a normal motor, looked down and temp was warmer than normal (my current normal :P).... I have a tach coming and it will be here tomorrow.

The coolant is supposed to flow through the heater core all the time. I was just making sure it isn't flowing through the heater core, and the radiator all the time, you have it plumbed correctly from your description.

You need a way to verify sensor values and check timing to make sure you are not chasing the wrong problem.

 

[87K5Newbe]

What was the engine temp when you measured the sensor resistance?

I don't expect the gauge sending unit to be that chart, only the EFI sensor, but it could also be a different sensor and that chart is wrong. I bet if you search the sensor part number you can find a resistance chart for it, though many GM temp sensors are the same values, not all.



The coolant is supposed to flow through the heater core all the time. I was just making sure it isn't flowing through the heater core, and the radiator all the time, you have it plumbed correctly from your description.

You need a way to verify sensor values and check timing to make sure you are not chasing the wrong problem.

Googled the temp sensor part number for a chart found several examples... essentally there is about a 300Ω +/-30Ω difference between the charts and the temp sensor depending on which chart I look at. so i think the temp sensor is fine. wish i could just read the MEFI data. Il have to take a look at the Rinda Techmate again. Also if there is a line on the timming cover like one of the posts you sent says. you would have to be a contortionist to see it!!!! Thanks again for all your help.