Engine will not maintain temps

[PJ Walters]

Good Morning Everyone, I have 1989 K5 with a crate 383/ holley sniper EFI. The truck is as basic as they come. I did a complete frame off and after a year I have it back together. I have been chasing a gremlin that I cannot figure out and I am about to go crazy! My truck will not maintain temp at highway speed. I start the truck and it comes to 185/195 fans kick on and it stays perfect. I jump in and drive and the temp plummets to 145F to 155F. My first change was a thermostat. I took out a 185F and installed a 195F. Same problem. I then thought the radiator was too big. Removed aftermarket 4 core and replaced with an OEM spec rad. Same problem. Figured water must be circulating when the thermostat was closed so I pulled off the top rad hose and looked into the tstat housing. I could stick my 90 degree pic tool in there and move the tstat all around. I thought I figured it out. So I machined a small metal ring to act as a shim to hold the tstat tight against the tstat housing assuring no water was moving around the tstat. Same problem. Guys, I have tried 3 tstats, 2 different radiators, 3 different tstat housings, various gaskets for the tstat housing and the truck is still circulating water when it should not be. I should tell you that I have two water temp sensors. One mechanical and one that is in my sniper system. I also have a IR gun and verified that both temps sensors are functioning. Could my water pump be too strong and it is not allowing the tstat to close once it pops open? I mean it has to be something about the water pump right? I literally changes every other mechanism in the cooling system. Please help this dude out before I go completely bonkers...

 

[Fastereddie]

What water pump are you running? I see you have no heater or bypass hoses on your pics. I suppose if it’s a nice high end water pump, it could be holding the t-stat open.

 

[dyeager535]

Pull your fan connectors off and go for a drive, or if possible, set the on temp to something like 220* and the off temp around 210* so they aren't on around the rates thermostat temp.

I can't believe the fans are that good (under cooling is far more common), but the thermostat sets the minimum temperature the engine will run at...if the engine runs at a lower temp, the coolant is somehow losing heat when it shouldn't be...such as being cooled when the radiator doesn't need assistance.

With decent ambient temps I'd find that hard to believe as a culprit, but I've absolutely seen it happen on my rig coasting downhill in cool weather that the temps will go under rated thermostat temperature. With no heater hose as a bypass, I'd have to agree, perhaps the pump is able to force the thermostat open.

 

[Fastereddie]

I would try running a bypass hose from your intake to water pump. That would relieve pump pressure from the t-stat.

 

[PJ Walters]

Thanks for the consideration everyone. As you can see (and others have pointed out) I don't even have a heater hooked to this thing yet. The fans do not kick on until they hit 195 degrees and turn off at 185. I know the fans work as they are engaged by the sniper unit. The fans are definitely not on when I am way cool. I think Fastereddie is on to something. It has to be a pressure issue and a bypass would allow the tstat to operate under normal conditions and not contend with a ton of pressure. I am trying it next and will advise!

 

[Wes Harden]

The fans come on to early.
Should only need 1 for engine cooling, and 2 when a/c is on, or over heating.
my personal preference would be at @210 on and 190 off.
At speeds over 40mph the fans shouldn't need to come on.
If you move the sensor to your radiator, the 195 on 185 off might work well enough.
The heater/bypass, helps keep the water pump from drawing water from under the t stat, creating an air bubble. This causes a spike in temp, before the t stat opens on cold starts.
Depending on water flow this could cause larger than normal temperature swings.

 

[dyeager535]

Thanks for the consideration everyone. As you can see (and others have pointed out) I don't even have a heater hooked to this thing yet. The fans do not kick on until they hit 195 degrees and turn off at 185. I know the fans work as they are engaged by the sniper unit. The fans are definitely not on when I am way cool. I think Fastereddie is on to something. It has to be a pressure issue and a bypass would allow the tstat to operate under normal conditions and not contend with a ton of pressure. I am trying it next and will advise!

If you set the fans for thermostat temp, then basically they will never stop running since they are fighting the t-stat, and with those being unpredictable in actual temp, a margin is a good idea I feel. Setting the fan temps above t-stat temp allows them to shut off when they are not needed (most often low load cruising) and keeps them from cycling as often when the load increases temporarily, like a small hill.

GMs settings on the small block with electric fan I want to say was 205 off and 220 on, so they obviously didn't feel there was any harm running the engine that high.

I also have two cooling fans but they are on separate circuits. With a good radiator I've never needed the second fan. But I don't have ac, I run manual trans, and my truck is pretty light. My preference even on my setup would be to run them staged, with the secondary coming on another 10* above the primary, if I could control them both with my ECM, which I can't for now. If I had AC I'm sure running them both when it was turned on would be the way to go, as mentioned.

Of course, not many have a problem like yours, and with a good electrical system dual fans running won't hurt anything. You may be perfectly fine with a bypass as the engine is designed for.

 

[Joel Wilson]

For starters, Dude, that is one clean rig. Very nice. I would really like to know where you got those seats, both front and rear.

I am curious about where your sensors are. Are the sensors for the fans in the same spot as the EFI and gauges? Different spots will have different readings and could be fighting each other depending on what they are controlling. Seems like the fans are coming on a bit too soon. I've never not had a heater plumbed in so I've never had a water pump pull so hard as to cause the water pump to open. Having said that, the rig I have now runs at just above T stat temp all the time unless its 110 or higher outside and I have my foot in it. I also run right at right close to GVW.

FWIW

Joel
norcal

 

[ridenby]

Very nice truck.

 

[PJ Walters]

For starters, Dude, that is one clean rig. Very nice. I would really like to know where you got those seats, both front and rear.

I am curious about where your sensors are. Are the sensors for the fans in the same spot as the EFI and gauges? Different spots will have different readings and could be fighting each other depending on what they are controlling. Seems like the fans are coming on a bit too soon. I've never not had a heater plumbed in so I've never had a water pump pull so hard as to cause the water pump to open. Having said that, the rig I have now runs at just above T stat temp all the time unless its 110 or higher outside and I have my foot in it. I also run right at right close to GVW.

FWIW

Joel
norcal

I just did a post about by seats in this forum. TMI out of California did mine. They have a nice website and system in place. I did the back seat as I stole it out of a 2013 minivan.

 

[PJ Walters]

UPDATE: The bypass made no difference at all. Once the tstat opened it never closed and water temp fell to 150F. I am going to set this thing on fire... Anyway, could not having a heater plumbed in cause too much "pressure" that the tstat can't close? Keep in mind that the next tstat I buy will be Tstat purchase number 5. Could my current tstat be damaged because of said pressure? I am going nuts over this because my Sniper cannot "learn" (goes into closed loop) below 160F so my rig runs like complete garbage. The make of my water pump is unknown as I bought my engine from a builder in Washington state. I have to send him an email and ask for the specs of the water pump. Other than this, I am fresh out of ideas. I have never heard of this problem before and apparently neither has a lot of the internet because results are sparse...

 

[MEMO43]

Have you tried running the sensor housing without the Teflon tape. That may help with the sensor itself grounding correctly. I had a similar issue an removing the Teflon help out.
Also how are your grounds, all sensors ground to the attachment point, might be worth a shot.
I've also seen temp sensors inline with the hose itself.
Agreed with everyone clean looking truck,
Let us know what the fix is.

 

[ryoken]

are we certain these temps are accurate? an I.R gun can be invaluable in these situations...


you could always try restrictor plates instead of a therm too...

 

[PJ Walters]

Have you tried running the sensor housing without the Teflon tape. That may help with the sensor itself grounding correctly. I had a similar issue an removing the Teflon help out.
Also how are your grounds, all sensors ground to the attachment point, might be worth a shot.
I've also seen temp sensors inline with the hose itself.
Agreed with everyone clean looking truck,
Let us know what the fix is.

Brother, I am fresh out of ideas and I will take any feedback, but I don't think the sensors are bad. I have an IR temp gun and it reads the same as the gages. I am still leaning towards a pressure issue.

 

[Fastereddie]

UPDATE: The bypass made no difference at all. Once the tstat opened it never closed and water temp fell to 150F. I am going to set this thing on fire... Anyway, could not having a heater plumbed in cause too much "pressure" that the tstat can't close? Keep in mind that the next tstat I buy will be Tstat purchase number 5. Could my current tstat be damaged because of said pressure? I am going nuts over this because my Sniper cannot "learn" (goes into closed loop) below 160F so my rig runs like complete garbage. The make of my water pump is unknown as I bought my engine from a builder in Washington state. I have to send him an email and ask for the specs of the water pump. Other than this, I am fresh out of ideas. I have never heard of this problem before and apparently neither has a lot of the internet because results are sparse...

Well, crap. I know you are on tstat # 5, but are they all from the same place? Years ago I was working on a 6.2, And had a bad glow plug controller. Changed it out and still bad. Everything in the troubleshooting guide said the controller was bad. Changed out again. Still bad. Changed out again. Still bad. Like you I was ready to light it on fire. Started calling other shops and the guy asked me where I was getting them from, I said Napa GP certain. He said try AC Delco one. It was cheaper and it fired right up. The guy said he went through a case of them they were all bad.
Just saying it can happen.
have you tested these in hot water to see how they act?

 

[Fastereddie]

Thermostat installed upside down?
Wrong water pump?

 

[PJ Walters]

Well, crap. I know you are on tstat # 5, but are they all from the same place? Years ago I was working on a 6.2, And had a bad glow plug controller. Changed it out and still bad. Everything in the troubleshooting guide said the controller was bad. Changed out again. Still bad. Changed out again. Still bad. Like you I was ready to light it on fire. Started calling other shops and the guy asked me where I was getting them from, I said Napa GP certain. He said try AC Delco one. It was cheaper and it fired right up. The guy said he went through a case of them they were all bad.
Just saying it can happen.
have you tested these in hot water to see how they act?

I had a Mr Gasket hi flow 185F tstat that came with the build. I changed that to a 195F tstat that I bought from napa. I then purchased an AC Delco from Amazon 185F tstat. I did the boil test for the fist two tstats and both opened slightly before their respective temp ranges to fully open at their settings to closed when removed. I am willing to try a fresh tstat again, but at some point I have to face the fact that I have a gremlin in that motor haha. Could there be anything internal that would cause this?

 

[PJ Walters]

The tstats are not upside-down, I promise. However, I do have a bone head question. I know they make reverse flow water pumps for a SBC. Could a reverse flow pump possibly have been installed causing the water to flow backwards and put the tstat open? Is that even possible? For the love of everything holy, we are talking about one of the most primitive systems on the entire truck. If anyone needs me, I'll be standing in my driveway dumbfounded... HA!

 

[Fastereddie]

The tstats are not upside-down, I promise. However, I do have a bone head question. I know they make reverse flow water pumps for a SBC. Could a reverse flow pump possibly have been installed causing the water to flow backwards and put the tstat open? Is that even possible? For the love of everything holy, we are talking about one of the most primitive systems on the entire truck. If anyone needs me, I'll be standing in my driveway dumbfounded... HA!

Sounds like the stat can be ruled out. I was thinking the same thing about the water pump. I really don’t know, but it is a variable you haven’t eliminated.

 

[bp71k5]

Where are you measuring the temp with the IR gun? FWIW, on mine there’s a 15F difference between the sensor in the head vs the sensor in the intake manifold. Just beware there can be a big difference on where the sensor is located. The head is typically the coolest spot on mine and the intake is the hottest.
I will echo what others said is that your fans should be turning on above your thermostat temp. My fans turn on about 215 and off at 205. I also have no heater.

My personal guess is that everything is fine and that the issue is the sniper sensor, its location, or the sniper itself. Plenty of people having goofy issues with the sniper.