Operating temp

[welpro222]

Hey guys, my truck runs hot when hitting a hill. My truck is a 87 suburban 6.2 th400, 4.10 rear, 37 bfg humvee tires. Runs great, recent head gasket job (head studs, felfro gasket used), 4 row radiator, 180 robertshaw thermostat. I installed a autometer electric gauge, mounted the sensor in the crossover tube near the thermostat housing.


For most of the time on the freeway it runs at 190 and climbs to 200 on slight hills. The other day i was climbing a decent grade for about a 1/2 mile and it climbed to nearly 220, then when I leveled out it started dropping. Is this normal temp readings near the thermostat? I still have the dummy light too, at what temp does this engage?

Thermostat is good
radiator came out of my blazer 6.2 and never gave me any problems even going over a mountain pass loaded down with camping gear. I even blew out all the gunk before installing in suburban.

I didn't change the water pump

Fan clutch is tight

fresh coolant added when i did head gaskets.

 

[cucvrus]

You were climbing the grade without a load? My M1009 does that when I have a loaded trailer on and it works justfine. I think that is fine. I have my temperature gauge hooked into the paseengers side rear upper head port. I have a transmission temperature gauge and that stays about the same as the engine even with an auxillary cooler. It is still passing thru the radiator and holds the heat. My 2014 Chevy engine and transmission goes that high on long hills. It runs 210 all the time. Modern technology. You gotta love it. I think the coolant allows it to run that hot without causing any issues.

 

[welpro222]

No load, but with the suburban itself, dana60 front and 14ff rear with 37 humvee tires. She's no light weight. I may have to hit a longer hill and see what she does then or even try slowing down and shifting into second. I can do 45-50 mph in second and be at 2500-2700 rpms.

 

[Drock]

It's supposed to have a 195° thermostat. Too low of a temp thermostat can cause overheating do to the fact that the engine will reach it's designed operating temperature (in this case 195°) and the stat will just stay open. Thus not allowing the coolant to stay in the radiator long enough to cool down.

 

[welpro222]

I did have a 190 robertshaw thermostat in it too, but same results except it would run mostly at 200.

 

[welpro222]

Is it possible the larger tires are putting too much strain on the engine?

 

[Drock]

Is it possible the larger tires are putting too much strain on the engine?

Yeah your trifecta of (heavy suburban) , (4.10 gears) ,and (37" tires), would be three factors that are putting much more strain on the engine. Do you have the timing advanced or the fuel turned up? Those can also cause over heating like you described. You mite have to upgrade your cooling system to handle your mods. A (2 core aluminum rad), and (maybe class III trans cooler), would definitely help.

 

[welpro222]

I already have a 4 row diesel radiator and a good cooler for my tranny (radiator style). Would a HO water pump help? Or an aux electric radiator fan?

timing is at factory line

 

[Drock]

I already have a 4 row diesel radiator and a good cooler for my tranny (radiator style). Would a HO water pump help? Or an aux electric radiator fan?

timing is at factory line

Old style 4 core copper rad's are actually less efficient then the new 2 core aluminum ones. Notice how ALL new cars and trucks use tiny little 2 core aluminum rad's these days. Stay away from 4 core aluminum ones though. More cores sounds better, but with aluminum rad's 4 cores can actually cause over heating.

 

[welpro222]

Is there a big temp difference between measuring at the crossover vs the factory location in the drivers head? Could it be off by 10-15 degrees?

 

[Barrman]

It has already been pointed out, but a 195° thermostat is what is supposed to be there. It really does make a difference. The coolant getting just a bit more time to stay in the radiator and let the heat transfer to the air is important. Going to a 195° should help some.

My M715 has a 6.2, NV4500, 8.87 axles and 38" tall tires. It was 7100 pounds empty the last time I ran it over a scale. About the same as your Suburban but without the curves you have. Autometer mechanical temp gauge in the drivers side head. I indicate 196°-198° going down the highway at speed in the Texas summer heat. Throw a hill in my way and it will go up to 202°-204° if I use the throttle to maintain speed. If it starts going higher, I just back off the throttle until it stablizes. Flat ground or down hilll gets it right back to thermostat temp. So does stopping with the engine just at idle.

Keep in mind this is a 30 year old engine that was designed to give the same output as a 2 barrel 305 gas V8 and get twice the miles per gallon. The speed limit was 55 mph nation wide when it was designed too.

 

[rsh4364]

Is there a big temp difference between measuring at the crossover vs the factory location in the drivers head? Could it be off by 10-15 degrees?

I read somewhere on a towing site that on the 6.2/6.5,at idle, heads are getting equal flow of coolant,but at 2500 rpms drivers side head is getting 76% of coolant flow.So the passenger side would be hot spot.Made me wonder about putting a rear coolant crossover on to help equalize flow.

 

[Skinny]

I have an M1031 on 37's which is a heavy brick which requires a full throttle approach to most anything. I have a mechanical Autometer guage in the driver side head. It reads 190 pretty much all the time once it comes up to temp and maybe pushes 200 on a super hot day being flogged up a hill. I do not see very large amounts of temp fluctuation. I think no matter how hard you work that engine, it should be capable of running within a threshold if everything is functioning correctly unless you are at max GVW, in the desert, and running a grade. Common sense should then kick in but other than that, I don't think your setup calls for a overheating issue.

 

[Keith_J]

It's supposed to have a 195° thermostat. Too low of a temp thermostat can cause overheating do to the fact that the engine will reach it's designed operating temperature (in this case 195°) and the stat will just stay open. Thus not allowing the coolant to stay in the radiator long enough to cool down.

WHAT? Thermostats are proportional devices, they moderate flow to maintain temperature. They are not Boolean devices, either open or closed but throttling devices, adjusting flow volume rate to keep temperature constant.

Now, with that being said, low flow rate from the coolant pump (AKA water pump although all engines should be using ethylene glycol coolant) can cause issues since pressure to flow area would be impacted.

The cooling rate of the radiator is dependent on air flow. Dirty fins or improper fan clutch can cause issues there.

Thermostats can fail soft, meaning they still respond but not fast enough. They are calibrated new, over time they leak coupling oil to the coolant or absorb coolant in between the wax pellet and coupling oil. Some cooling systems can cause the open failure, on the 6.2 DD engine, they fail in the more closed state.

 

[Drock]

WHAT? Thermostats are proportional devices, they moderate flow to maintain temperature. They are not Boolean devices, either open or closed but throttling devices, adjusting flow volume rate to keep temperature constant.

Now, with that being said, low flow rate from the coolant pump (AKA water pump although all engines should be using ethylene glycol coolant) can cause issues since pressure to flow area would be impacted.

The cooling rate of the radiator is dependent on air flow. Dirty fins or improper fan clutch can cause issues there.

Thermostats can fail soft, meaning they still respond but not fast enough. They are calibrated new, over time they leak coupling oil to the coolant or absorb coolant in between the wax pellet and coupling oil. Some cooling systems can cause the open failure, on the 6.2 DD engine, they fail in the more closed state.

Ha! Super smart computer guy overthinking an analog era system . Forgive me, I don't have the eloquence or vocabulary that you do to overly explain my point, so here's the simple explanation as I understand it. The radiator is a heat exchanger, if the coolant passes through it too fast it won't be cooled properly and will slowly overwhelm the process and over heat. These diesel trucks are designed to run at 195°, and WILL weather we like it or not sometimes. Putting a lower opening temperature thermostat in can cause over heating because it will just stay open and never close. Thus not keeping the coolant in the rad long enough to cool down. Now that being said you mite be able to run ah 180° if you had ah better heat exchanger I.E. more efficient radiator and better cooling fans. However running too cool has it's own list of problems, the main one being inefficient combustion. The best scenario in this case would be a really great radiator + cooling fans, managed buy ah 195° thermostat. This way the system could have ah better ability to cool the engine down IF needed. Like having backup cooling on hand.

 

[welpro222]

I'm going to be hitting the logging roads this sunday, I'll let you know how it does temperature wise.

It reacts the same way regardless if its a 180 or 190 thermostat, but with a 10 degrees difference. The 190 thermo should be fully open at 212, my truck should not get any hotter then that. But with either thermostat it have reached 215 nearly 220 on the same hill.

 

[welpro222]

Well the truck did great going up the logging roads (11-12 miles of 15 mph climbing). Did not get over 190 temp. I guess i just need to watch my speed and rpm combo if I'm going to be hitting any mountain passes.

 

[sschaefer3]

Mine will go up to 220 if I am going 70mph up the hill. If I slow down it goes down quick. If I drive slower it stays lower. This is an M1008 with 37's. This was last weekend in Arizona 103 degrees where I was out side too. With my add on AC running.