I'm having some issues with running hot / overheat that we can't seem to figure out.

96 B3500 5.9 with 63k miles

Put it in the Hughes air gap. At the same time we did some other preventative work

new thermostat
new water pump
new radiator (old one was operational but corroding)
new plugs, wires, etc
new ECT sensor and sender

engine used to run 205-215 in south FL

now it runs 230-240 and I can get it to go higher if I try.

Fan clutch wont kick on at all. Today I got it to 260.

We changed the thermostat. Have bled the system a bunch of times. I just tried burping it again on a good incline (private boat ramp, probably 4ft or so elevation change between axles

chsnged the fan clutch

it appears coolant is flowing ok although I don't know what the rate should be. Once it's warm with the cap off it starts to flow. When I rev it the flow increases substantially

so I don't think it's air in the system

any other ideas to check? Hughes just says to check the sensors (they seem fine, verified with mechanical gauge) and bleed the system. We also tried with a vacuum bleeder. I really don't think it's air.

Thanks!

 

Are these temperatures taken when it's sitting still or when driving?

 

Driving or just revved in driveway. Stop and go or highway at 70mph, makes no difference. Idling it will slowly climb. Once it reaches 230, it won't drop down below even if just idling and the new thermostat is a 180.

In contrast, it never went above 225 before this. Fan could come on and it would never elevate above that even climbing long grades at high RPM like crossing the great divide coming from UT up to WY and then would drop back to 200-205 when back on the flat.

 

Bad thermostat, or bad temp sensor, or still air trapped in the system.

 

Thermostat has been replaced 3x (and boiled to test). It flows when open and has been confirmed.

Temp sensors on this model only send info to the gauge and PCM (separately, there is a sensor and sender) but the clutch is mechanical. There are no electric fans.

If you have ideas how to check for air in the system in ways I haven't tried I'm all ears. But I've had the cap off, temp at 220 and the coolant is flowing like mad at 2000rpm. I'm just not sure how an air bubble could be causing something with that much flow happening.

 

What brand thermostat? Does it have a little hole in it, or the 'wiggler' to allow air to easily escape?

Yeah, two sensors, a one wire for the gauge, and two wire for the PCM. One wire sensor grounds thru the manifold, didn't put any sealer on the threads did you??

Might be interesting to pick up a cheap IR thermometer, and see what it thinks your temps are. If you have a scanner that will read data, wouldn't hurt to compare what the PCM thinks temp is, to what the gauge has to say either.

Changing the intake shouldn't cause overheating..... Gotta be something else going on there.

 

I forget the thermostat brand, I'd have to check on those details. I almost drilled it just in case, but man it has got to be opening because the flow in the radiator is heavy when it's open and RPMS are up. There's no way it's just from the bypass.

I do have an IR gun. I've checked lower and upper hoses, radiator, fan clutch, the intake, etc. They all seem to coincide with what the PCM (scangauge hooked up to that for readout) and the dash gauge point to.

I agree I don't think it's the intake, I just don't know what else to do at this point. Change the radiator again?

 

Have you flushed the block? How is heater performance?

With pretty much everything being new....... the system should perform flawlessly. If you have good flow, which you apparently do...... I have no idea why it would still be overheating.... On my truck, I know some air got trapped below the thermostat, so, initially, the engine would get pretty warm before the stat actually opened, but, once it cycled a couple times, temp would stay right where it is supposed to.

 

The heater works fantastic! It's blasting 240degree air at me lol!

we didn't do a "flush" per se but it's been drained and filled a bunch of times now, vacuum filled, burped with the radiator high, etc.

i really dont think air is the issue. I mean it's flowing like a rushing river at 220 with the radiator cap off and the engine at 2k rpm.

We are at the 2 week mark now. gonna Change the fan clutch again and see what that does.

I had the IR gun on stuff again today, 215 or so on radiator inlet and 185 on discharge. Fan clutch at 225, ECT sensor showing 233.

That was after stopping and I got it to about 245, it just cooled a bit when stopped. Idling brought it back to 210 range but the minute I drive it again it can get up to 235.

While that is in range, my concern is it will climb without anything stopping it when there is load or constant high RPMs. It was boiling yesterday.

 

The fan isn't on backwards, or spinning the wrong direction is it??