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Neal, Chevy Mechanic
Category: Chevy
Satisfied Customers: 8351
Experience:  Shop Owner and Mechanic on multiple makes.
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Why does my truck run HOT!

Resolved Question:

Why does my truck run HOT!
Submitted: 6 years ago.
Category: Chevy
Expert:  Neal replied 6 years ago.
Welcome to JustAnswer, I'm here to help get your problem resolved. Please feel free to ask follow up questions, it is part of the process.

Here are a couple of thoughts, without being there It is impossible for me to give you a definitive answer but I can help you troubleshoot.

How much was the engine bored and did they check the cylinder wall thickness?

Was it running hot before being rebuilt? Possibility of cracked block or head.

I know you said the radiator is clean but one possibility is reduced radiator capacity. Over time the radiator can collect sediment that cannot be flushed out. To check this get the engine up to normal temp and turn it off and then being careful of the fans which can still turn on, compare the temp at the bottom of the radiator to the temp at the top of the radiator, if it is colder at the bottom than the top, that is a sign it is partially plugged and the capacity is reduced.

Customer: replied 6 years ago.
It is a very good Machine shop. Engine was still showing crosshatch in cylinders - bored either 10 or 20 over to correct slight taper in front 2 cylinders, magnafluxed, thorough inspection, all dimensions checked, heads rebuilt with same level of quality. Radiator is fairly new and clean, replaced @16 months ago due to crack in plastic side tank from earlier accident. Flushed with hose, out of vehicle, all came out clean after coolant rinsed out. I asked a retired ASE mechanic to look at it, that's when we took the thermostat out. He and I are both confident the radiator is ok. I can't see all of "what I tried" not sure if you can. If not visible, I can e-mail to you.
Expert:  Neal replied 6 years ago.
I cannot exchange phone or email by the site rules but you can put it in the next reply.
Customer: replied 6 years ago.
Engine warms up quickly and runs hot - @235 degrees, computer sets code, dramatically affects performance.

Plenty of coolant, radiator clean, fan installed correctly, plenty of air circulating thru radiator, fan clutch operating normally, water pump seems normal (no noise, no leaks, good crossflow in radiator).

Replaced thermostat – NO CHANGE – everything remained the same, engine runs @ 235 degrees, code, performance issues.

Removed thermostat – Engine warms up slowly and operating temp varies. Runs cool, @160-180 most of the time, creeps up to @200 on hottest days, engine performance good!

Installed new 195 degree NAPA premium grade thermostat. Engine runs hot again @225-235, computer sets code, performance issues. When at 235, turn heat on full blast, engine cools @10-15 degrees.
Expert:  Neal replied 6 years ago.
Timing set at 0?

Valve lash set properly?

Stock cam?

If all of those check out, it has to be that the reduced thickness of the cylinder walls are too much for the capacity of the cooling system with the thermostat in place. This is partially verified by the fact that running the heater uniformly reduces the engine temp.

You may either have to run it without the thermostat or figure out a way to fit a bigger radiator or install a auxiliary high capacity electric fan.

Customer: replied 6 years ago.
YES, timing at 0, stock cam, valve lash set 3 times by the book (wanted to make sure I had it right). I just verified w/my machine shop, it was bored 20 over. Cylinder walls should be thick enough. This shop will not bore anything over 40 as that may cause this issue. I'm baffled, unless I got 3 bad thermostats, and what are those odds. They recommended I try a 160 thermostat as a temporary (and maybe permanent) solution.
Expert:  Neal replied 6 years ago.
I don't think the 160 will help, if it won't cool with the 195 wide open, why would it cool with the 160 wide open. It may not get hot as fast but it will still get to the same temp in the end.

What about a high quality electric fan? You can even run it on a temp switch so you don't have to turn it on and off manually.
Customer: replied 6 years ago.

Thanks Neal for your suggestion. I would rather find out why it won't cool with a stock set up. I will take the thermostat out tonight and run it. Meanwhile, I will continue to research for my answer. If all else fails, I will consider an electric fan.



Expert:  Neal replied 6 years ago.
Sorry I could not give you a definitive answer.
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