1998 k2500 454 getting hot

[1998_K1500_Sub]

Running the truck empty with no load runs 215° down the highway, pull off and it creeps up to about 225° within 10-15 seconds.

What happens if you then put it in neutral and rev the engine to 2000RPM? Doing so should circulate coolant rapidly throughout the engine, equalizing temperatures.

 

[grey wolf]

Just going to throw this out there, but maybe you've got an air bubble trapped in the cooling system somewhere? I don't really have any experience with big block stuff, but I know some engines can be a real pain in the ass to get the air out when you refill the cooling system. The funnel shaped tool that someone posted earlier is a good tool, I use that one all the time. Turn your heater on, so you know you have coolant flow through the heater core too, then get the engine up to operating temps by holding it at maybe 2500 RPM or so, until the fan starts cycling. Then let it idle, top up the coolant in the funnel if necessary, and then blip the throttle a few times, right up to like 4000 RPM, and let it idle for a minute. You'll see some air bubbles working their way up to the radiator and out through the funnel. The idea of blipping the throttle is that it is pushing the coolant through the system each time you hit the throttle, hopefully forcing any air bubbles out of lower flow areas. Keep topping up the coolant as necessary. Keep that up until you don't have any more air bubbles coming out of the radiator. Then when you are sure you've got all the air out, shut the engine off, take the funnel off and install your rad cap.

On the other hand, I'd think if you were hitting 235F easily just by driving normally, it would be pretty easy to make it overheat and boil. Most electric fans are coming on around 220F or so on cars I've worked on. As it has already been mentioned, maybe your temperature sensor reading is just being taken at a hot spot in the cylinder head (which will naturally be the hottest area of the cooling system), and it's not really a great indicator of true engine coolant temperatures. I am curious to know, when you find out, what the problem was.

 

[454cid]

So I checked the dually and the exact replacement I have on the shelf and I can't get eyes on how many cores it has with the fins in the way, so I'll simply choose to believe I'm right.

Look under the cap with a flashlight.

 

[newguyinnc]

What happens if you then put it in neutral and rev the engine to 2000RPM? Doing so should circulate coolant rapidly throughout the engine, equalizing temperatures.

Driving down the highway at 70mph gauge says 215. If I pull off at an exit it'll climb to 235. If I rev it to 2000 rpm it'll quickly come back down to 215. The whole time it's doing this, the ECU sensor in the intake is reading around 200°.

 

[newguyinnc]

Just going to throw this out there, but maybe you've got an air bubble trapped in the cooling system somewhere? I don't really have any experience with big block stuff, but I know some engines can be a real pain in the ass to get the air out when you refill the cooling system. The funnel shaped tool that someone posted earlier is a good tool, I use that one all the time. Turn your heater on, so you know you have coolant flow through the heater core too, then get the engine up to operating temps by holding it at maybe 2500 RPM or so, until the fan starts cycling. Then let it idle, top up the coolant in the funnel if necessary, and then blip the throttle a few times, right up to like 4000 RPM, and let it idle for a minute. You'll see some air bubbles working their way up to the radiator and out through the funnel. The idea of blipping the throttle is that it is pushing the coolant through the system each time you hit the throttle, hopefully forcing any air bubbles out of lower flow areas. Keep topping up the coolant as necessary. Keep that up until you don't have any more air bubbles coming out of the radiator. Then when you are sure you've got all the air out, shut the engine off, take the funnel off and install your rad cap.

On the other hand, I'd think if you were hitting 235F easily just by driving normally, it would be pretty easy to make it overheat and boil. Most electric fans are coming on around 220F or so on cars I've worked on. As it has already been mentioned, maybe your temperature sensor reading is just being taken at a hot spot in the cylinder head (which will naturally be the hottest area of the cooling system), and it's not really a great indicator of true engine coolant temperatures. I am curious to know, when you find out, what the problem was.

When the new motor was installed, the coolant was vacuum filled. Been working on this stuff for 35 years and it's got me baffled.

 

[smokymtn65]

If you have a small camp stove /burner boil some water and pull sensor and hold it in and compare guage reading. On this sensor is it higher resistance higher reading? Anyone know? Maybe wire corroded internally? Was cam degreed in when build was done?

 

[newguyinnc]

If you have a small camp stove /burner boil some water and pull sensor and hold it in and compare guage reading. On this sensor is it higher resistance higher reading? Anyone know? Maybe wire corroded internally? Was cam degreed in when build was done?

Cam was degreed when built. I've had 3 thermostats in this engine and stove tested the last 2. Verified dash gauge with auto meter mechanical gauge. On cold start up, if you watch the gauge you can see the thermostat cycle at 195° the first time. After the first cycle it goes to 215° and stays there. Start driving and it stays at 215°. Stop at a light and in 10-15 seconds it'll climb to 235°. Start going again or rev the motor and it'll drop back to 215°. My intention was to use this truck to tow a small enclosed trailer out of state frequently. Don't trust it with this issue. Motor doesn't have nearly the low end power I expected given what my 2000 OBS has with 185,000 miles on it. Same motor and transmission in the 98 and the 2000. The 2000 runs 195-200° no matter what you throw at it. The 98 is my gremlin.

 

[Keeper]

I'm still stuck on it not breathing at idle. Assuming 50/50 mix.... throw a 180 tstat and an 8 lb rad cap on it to lower the boiling point by 24 degrees and see if the system will "breathe" at a number that is acceptable for you.

 

[BeXtreme]

It sure sounds like a water pump or clogged water passage problem. Are you sure the correct L29 head gaskets were used? They aren't the same as Gen V and previous head gaskets, but they will interchange freely. Putting a previous generation BBC head gasket on a Gen VI and vice versa can cause similar issues to this.

 

[newguyinnc]

I'm still stuck on it not breathing at idle. Assuming 50/50 mix.... throw a 180 tstat and an 8 lb rad cap on it to lower the boiling point by 24 degrees and see if the system will "breathe" at a number that is acceptable for you.

I tried the 180° thermostat and it made no change. It is 50/50 mix currently in it now.