Every Time I Try to Outsmart GM Engineers, I Get the "smack down" (Fixed)

[1-ton]

During the build of my 1991 V3500 I have tried a couple of things that I thought where going to be an improvement over the original design that GM engineers made only to fail, and have to take it back to the original GM design.

Right now the issue is the coolant temp. I thought I was going to be slick, and put water restrictors into the thermostat housing, in order to do away with thermostat failures I have had in the past on some of my other trucks. The problem is that my coolant temps are all over the place. One minute the truck is running at 200 degrees while idling at a stop light in the sunlight, then 20-minutes later as the sun is going down and I am driving down a hill the coolant temp is at 150-degrees. My OBD-I/ECM is probably going nuts trying to figure that much temp fluctuation out. I am going to put a thermostat back in, so that I can get more consistent coolant temps. The OE thermostat is supposed to be a 195-degree thermostat, but I was thinking of trying a 180-degree one first, and see how that works. Any thoughts or suggestions?

Moroso Water Outlet Restrictors. I have the blue one in it now.

 

[rampage]

Why are you trying to ‘improve’ the thermostat? It’s designed to run at 195 for a reason (fuel efficiency IIRC).

 

[1-ton]

Why are you trying to ‘improve’ the thermostat? It’s designed to run at 195 for a reason (fuel efficiency IIRC).

Back when I had a 195-degree thermostat in my 1991 V3500 trucks old engine, the engine temps where running at about 210 to 230 Degrees consistently, which is why I was thinking of trying a 180-degree thermostat. If the same temp range holds true for the 180 thermo as it did for the 195 thermo, then it should run in about the 190 to 210 range.

 

[nvrenuf]

If it's running that much higher than the thermostat (up to 230) you likely have another problem.

My old 91 crew cab with a stock 350 stayed on 210, once it got up to temp there were no changes.

 

[ChrisPerry]

Are those temps measured with an IR gun or by the dash gauge? Is the cooling stack clean? Possibly change to a fan with more blades for better air flow.

Be sure to test the thermostat in hot water to be sure it is opening at said temp. Some have been known to be 10+ degrees off in either direction.

 

[1-ton]

If it's running that much higher than the thermostat (up to 230) you likely have another problem.

My old 91 crew cab with a stock 350 stayed on 210, once it got up to temp there were no changes.

If the 180-degree thermostat I am going to install is capable of holding a very consistent temp range, then I will take it out, and go to an OE 195-degree thermostat. Hopefully it will get the same 210-degree consistent operating range like yours did.

Are those temps measured with an IR gun or by the dash gauge? Is the cooling stack clean? Possibly change to a fan with more blades for better air flow.

Be sure to test the thermostat in hot water to be sure it is opening at said temp. Some have been known to be 10+ degrees off in either direction.

The temps I am quoting are from the gauge. The engine in my truck is brand new with only 500-miles on it. The only problem I am having is with temp fluctuation because of the coolant restritor disk modification I did. I am going back to the factory design of a thermostat, in order to get a more consistent temp operating range that my OBD-I/ECM can properly function at.

 

[diesel4me]

Those restriction washers were designed for race cars that have high rpms all the time..and coolant flow is at its peak,it needs to be slowed down some to let it stay in the radiator long enough to transfer heat..

A thermostat doesn't just "open",it is constantly opening and closing to regulate and maintain its rated temperature when the coolant flow changes and load conditions make the coolant heat up more..

In my experience a 195 degree thermostat ,what GM used since 1968,seems "best" for my climate..it lets the engine warm up faster and provide good heat from the heater,and it doesn't stay above 90 degrees around here often or for long,so as long as the rest of the cooling system is in good condition,it should not overheat..

I have tried using 180 and 160 degree thermostats to "solve" an overheating issue,but all they did was delay the onset of the boiling and peuking of coolant by a few more minutes...gas mileage suffered too,and crankcase dilution and condensation build up in the winter when you do short trips around town can happen,and be quite harmful to the rest of the engine if it runs at a too cold temperature..sludge forms,things rust up inside...

The factory has done all the engineering and testing for us--I too like modifying things hoping to improve them,but sometimes you can't re-invent the wheel...granted some designs are crappy and do need improvement though..

 

[1-ton]

Those restriction washers were designed for race cars that have high rpms all the time..and coolant flow is at its peak,it needs to be slowed down some to let it stay in the radiator long enough to transfer heat..

A thermostat doesn't just "open",it is constantly opening and closing to regulate and maintain its rated temperature when the coolant flow changes and load conditions make the coolant heat up more..

In my experience a 195 degree thermostat ,what GM used since 1968,seems "best" for my climate..it lets the engine warm up faster and provide good heat from the heater,and it doesn't stay above 90 degrees around here often or for long,so as long as the rest of the cooling system is in good condition,it should not overheat..

I have tried using 180 and 160 degree thermostats to "solve" an overheating issue,but all they did was delay the onset of the boiling and peuking of coolant by a few more minutes...gas mileage suffered too,and crankcase dilution and condensation build up in the winter when you do short trips around town can happen,and be quite harmful to the rest of the engine if it runs at a too cold temperature..sludge forms,things rust up inside...

The factory has done all the engineering and testing for us--I too like modifying things hoping to improve them,but sometimes you can't re-invent the wheel...granted some designs are crappy and do need improvement though..

I live in sunny Las Vegas where an engine can really start to climb in temperature while idling at a stop light, or going up a street that has a bit of an incline to it.

 

[diesel4me]

No doubt in hotter climates and higher altitudes the engine will heat up more,especially with A/C ..but once it reaches 195 degrees,it should climb not much more than that...I've had a few vehicles that ran at 220 degrees in the summer,but never boiled over or gave any grief..

The "operating" temperature is maintained by the thermostat,but what keeps the coolant from boiling is a combination of things,like the total capacity of coolant,bigger engines need more of it,and the size of the radiator,to dissapate the heat rapidly enough,and the coolant being pressurized to 16 psi or so...granted if your climbing Pike's Peak,the stock cooling system may be insufficient to prevent a boil over...

 

[vandelay industries]

Describe your exact setup now. i think the computer WANTS to see 210-220. 200 degrees in Lost Wages sunlight during the day is not bad.

 

[TreeFarm]

thermostat sets minimum temperature. Your cooling system sets max temp. once the thermostat is open, its up to the cooling system to keep it from climbing above thermostat temperature. better fans, rad, coolant capacity, lower hose not collapsing, all that stuff keeps you from climbing too much above thermostat.

 

[1-ton]

Describe your exact setup now. i think the computer WANTS to see 210-220. 200 degrees in Lost Wages sunlight during the day is not bad.

It is a brand new GM Goodwrench crate engine with only about 500-miles on it. It has a new water pump, new radiator, new radiator cap, all new hoses The fan is the original fan it came with and a new heavy duty Hayden clutch fan. Pretty much all stock.

 

[obijuank5]

What coolant did you put in it?

 

[1-ton]

What coolant did you put in it?

Regular old green 50/50. I am not having an issue with over heating, just an issue with inconsistent temp fluctuation because of the modification I did with the coolant restrictor washers, and I need to go back to a thermostat, in order to get consistent coolant temps.

 

[dyeager535]

Problem nowadays is that it seems most/all thermostats are garbage. If you find one that works, don't change it unless it fails. The one in my truck was put in ~2000, and it will stay there until I have a problem with it.

Even high dollar stuff isn't guaranteed to be good out of the box. I hesitate to lean towards AC Delco on these, but no one seems to be able to make one that consistently works anymore, and if taking wild stabs at things, might as well consider them.

Stick with 195*, for a variety of reasons. It's not just emissions.

 

[bp71k5]

If the temps are fluctuating that much, it may be because the probe isn't fully immersed in coolant. If you used a reducer, sometimes the probe doesn't go all the way into the coolant and if you have air in the system, that'll make it worse. Actual temp also depends on where the probe is. I have three coolant sensors and two of them are in the intake (one for fans and one for the ecm) and the two in the intake read about 195 which is what my thermostat is, while the one in the head (for my temp gauge) reads 20-30 degrees lower. Something to be aware of.

 

[Justin V]

I'd think the temp gauge probe is bunk...


The head should be the hottest...

 

[bp71k5]

I'd think the temp gauge probe is bunk...


The head should be the hottest...

It looks correct from everything I've checked. I think the intake tends to be hotter because all the hot coolant exiting the head goes back to the intake under the thermostat. The probe is right next to the thermostat so the water can't get any hotter than it is right there since it goes to the radiator after it leaves the thermostat.

The sender/probe in the head is only exposed to coolant from 1 or 2 cylinder walls and also has fresh coolant entering the area before it's heated from combustion. So it makes sense that it reads a bit cooler.

 

[Justin V]

Fine...

Go ahead and use your smarts on me.

 

[paratrooper307]

thermostat sets minimum temperature. Your cooling system sets max temp. once the thermostat is open, its up to the cooling system to keep it from climbing above thermostat temperature. better fans, rad, coolant capacity, lower hose not collapsing, all that stuff keeps you from climbing too much above thermostat.

This. A lot of people want to play around with thermostats because their vehicle runs hotter than they think it should. Changing to a lower temperature thermostat has no impact on your maximum temperature once warmed up-that's determined by the overall efficiency and health of your cooling system. Using a temperature setting other than factory merely confuses the computer unless you change the program to take advantage of it.