Am I overheating?

[Kelpiesgmc]

I put in a new S&J motor. New Superior aluminum radiator, new RS thermostat, new fan clutch, new temp sender. Burped the coolant for quite a while. After a very short drive around the block my temp gauge starts creeping past 1/2. I got the IR gun out and read the temp of the upper radiator hose and the top-driver's side of the radiator. I'm reading 190-220 (it's ~90° outside). It doesn't seem to get any hotter than this. Not sure if this is a normal temp.

If I let it run and continue to IR gun it, the temps seem stable, but by this point the temp gauge is nearly pegged to H.

I replaced the temp sender with another new one and got the same results. Also replaced the new fan clutch with another new fan clutch. Same results.
I never hear either fan clutch engaging. I might put a screw through one so it's always on to see what happens...

I measured the resistance of the temp sender at ~80 ohms.

I really want to be careful with the new motor! Not sure how to proceed

 

[Carl Stouffer]

It's kind of typical to have a new engine run a little hotter than normal until broken in. If you have a 195 degree thermostat in it, the temp seems to be not too out of line.

You should definitely be hearing the fan clutch engage though.

 

[tmsnyder]

what p/n fan clutch did you install?

If you overheat, you will know. The wet overheat, where it boils out coolant, would happen first. The coolant is still protecting the engine from temperatures above 220 or so, and you would shut it down if you saw any sign of that.

I think you need a better gauge, even if it's temporary, on the engine.

 

[LQQKatJon]

I put in a new S&J motor. New Superior aluminum radiator, new RS thermostat, new fan clutch, new temp sender. Burped the coolant for quite a while. After a very short drive around the block my temp gauge starts creeping past 1/2. I got the IR gun out and read the temp of the upper radiator hose and the top-driver's side of the radiator. I'm reading 190-220 (it's ~90° outside). It doesn't seem to get any hotter than this. Not sure if this is a normal temp.

If I let it run and continue to IR gun it, the temps seem stable, but by this point the temp gauge is nearly pegged to H.

I replaced the temp sender with another new one and got the same results. Also replaced the new fan clutch with another new fan clutch. Same results.
I never hear either fan clutch engaging. I might put a screw through one so it's always on to see what happens...

I measured the resistance of the temp sender at ~80 ohms.

I really want to be careful with the new motor! Not sure how to proceed

If you have a new engine…. A good engine temp gauge is a cheap investment.

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I eliminated the “christmas tree” vacuum switch on the front passenger side of manifold and installed the trmo sender there to retain the stock one.

Your IR readings seem fine. But you better be sure!

Lastly…. How much antifreeze did you add? A new engine/radiator can be tricky to fill. It can air lock. So if you did not add like 6 gallons. You might not be full. Make sure your overflow bottle is working and let the engine cool and check your radiator level. If you only was able to get 3 gallons in…. You probably dont have a full system.

 

[Kelpiesgmc]

Okay. I got and tested a mechanical temp gauge. I drilled two screws into the front of the fan clutch to rule it out as a factor. Drove around about 1/2 mile with my eyes glued to the gauge. And I noticed something weird. It was hovering around 220° and suddenly jumped to 240° stayed there for a few seconds and slowly creeped back to ~220°. I watched it a while longer and it stayed in 220°-230° range for quite a while. Then did the momentary 240° jump again. I ran out of time to tinker with it for the day so I shut it off.

Is this expected!? Seems very odd.

 

[jampants]

I can't help with your diagnosis but I can give you a reference point that may be useful.

I'm running the same setup as you, new S&J motor with the Jim B. spec'd build, new "Superior" Radiator etc. Can't remember what thermostat I'm running though. I see temps no more than 180. In fact it pretty much slowly warms up and is then pegged at a whisker over 180F after 10mins or so. Hills, flat whatever never seem to budge the dial - assuming my dial is correct!

A digital sender and gauge can defo help. My old Oil Pressure gauge still in the dash always reads 50-60psi responding v slowly. My digital oil pressure gauge with its own sender measuring at the same point jumps around wildly but within a sensible range and defo responds to what the engine is actually doing instantly. It is much more reassuring its actually giving me a proper realtime reading.

This is my oil pressure sender;

https://www.amazon.com/ZHSYMX-Universal-Pressure-Gauge-52mm/dp/B0DJLJ4QVC

This is their same water temp gauge with sender - Your post has prompted me to order one of these

https://www.amazon.com/dp/B0CJ4G3H12?sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWw

 

[LQQKatJon]

Okay. I got and tested a mechanical temp gauge. I drilled two screws into the front of the fan clutch to rule it out as a factor. Drove around about 1/2 mile with my eyes glued to the gauge. And I noticed something weird. It was hovering around 220° and suddenly jumped to 240° stayed there for a few seconds and slowly creeped back to ~220°. I watched it a while longer and it stayed in 220°-230° range for quite a while. Then did the momentary 240° jump again. I ran out of time to tinker with it for the day so I shut it off.

Is this expected!? Seems very odd.

That seems like low on coolant.

 

[Kelpiesgmc]

That seems like low on coolant.

After it cools off I remove the radiator cap and it's full to the top

ChatGPT suggests that pockets of vapor could cause the sudden spike in temperature. It's unclear to me if that vapor is being created by a hot spot in the engine, or if it's just an air bubble I didn't get out while burping the system.

Well I guess I'll try burping some more, or see if I can get a hold of a Radiator Vacuum Filler.

 

[LQQKatJon]

After it cools off I remove the radiator cap and it's full to the top

ChatGPT suggests that pockets of vapor could cause the sudden spike in temperature. It's unclear to me if that vapor is being created by a hot spot in the engine, or if it's just an air bubble I didn't get out while burping the system.

Well I guess I'll try burping some more, or see if I can get a hold of a Radiator Vacuum Filler.

Vacuum filler is not needed. You should not need to go to that extreme.

What pressure radiator cap do you have and is it for sure working? Should be 9psi.

And is the overflow bottle working. You should have to add a little antifreeze to the overflow bottle after a couple heat cycles. You should see the bottle level raise a bit when the engine is at temp. And then retract when cooling. Many gmc’s the hose falls off or is missing on the inside of that overflow cap.

Make sure that is working.

Also what fan clutch? Should be a end #47. Or “heavy duty”. And really pay attention to the fan direction…. I have seen fans flipped 180.

 

[Kelpiesgmc]

Vacuum filler is not needed. You should not need to go to that extreme.

What pressure radiator cap do you have and is it for sure working? Should be 9psi.

And is the overflow bottle working. You should have to add a little antifreeze to the overflow bottle after a couple heat cycles. You should see the bottle level raise a bit when the engine is at temp. And then retract when cooling. Many gmc’s the hose falls off or is missing on the inside of that overflow cap.

Make sure that is working.

Also what fan clutch? Should be an end #47. Or “heavy duty”. And really pay attention to the fan direction…. I have seen fans flipped 180.

I have a 16psi cap that seems to be working and I have a 9psi cap from applied on the way. The overflow reservoir looks normal. It expands to HOT when hot and back to COLD when cold.

Currently my fan clutch is 100% engaged since I drove two screws into the front of it to rule it out as a problem.

The fan has FRONT engraved on one side so I made sure that faced the radiator.

I also have the two piece fiberglass fan shroud from Applied installed.

I measured the temp of the lower radiator hose when hot and it's a cool 130°-140°

 

[Kelpiesgmc]

In case it's related I should also mention: I have run-on every time I shut the engine off. There's also a "sneeze" out the carburetor before it stops. I guess that means I am running lean? Perhaps that's causing the engine to run hot? This weekend I will try adjusting the mixture screw so see if that has a positive effect.

 

[Bhart]

A carbureted engine "diesels" (also called run-on) when it continues to run after the ignition is turned off, due to hot spots in the combustion chamber igniting the fuel without a spark. Common causes include carbon buildup, high idle speed, excessively advanced ignition timing, lean fuel mixtures causing overheating, and a faulty anti-dieseling solenoid or dashpot on the carburetor.

 

[Kelpiesgmc]

A carbureted engine "diesels" (also called run-on) when it continues to run after the ignition is turned off, due to hot spots in the combustion chamber igniting the fuel without a spark. Common causes include carbon buildup, high idle speed, excessively advanced ignition timing, lean fuel mixtures causing overheating, and a faulty anti-dieseling solenoid or dashpot on the carburetor.

Yeah that's what AI told me too, but it's not clear to me if the hotter ignition temps raise the engine temperature enough to account for what I'm seeing—settling around 230° under the light load of strolling around the block on flat ground.

 

[LQQKatJon]

Yeah that's what AI told me too, but it's not clear to me if the hotter ignition temps raise the engine temperature enough to account for what I'm seeing—settling around 230° under the light load of strolling around the block on flat ground.

Gmc dieseling is usually a timing issue.

You might want to check tdc. The replacement timing tab sometimes are not great. Or a harmonic balancer can be off.

 

[Kelpiesgmc]

I messed with it a bunch today and I'm beginning to fear that something is blocking a water passage, or that a (brand new) head gasket is blown.

I messed with the air-fuel mixture and the sneezing and run-on weren't happening anymore.

I burped the cooling system again and saw no air bubbles through multiple thermostat opens/close cycles.

At idle I was seeing pretty steady temps of 180°-220° (95° day). I idled while gently revving for quite a while and everything held steady.

However, the moment I drive (on flat ground) the temps climb to the 230°-240° range.

This time no sudden spikes. Just stays hot till I shut it down so as to not do damage.

The heater air doesn't feel extremely hot. I'd guess around ~100°, which feels like a clue of some kind.

Only easy thing I can think to try at this point is to temporarily remove the thermostat to rule out it restricting flow.

I think if that doesn't change the situation I'm going to have to start taking things apart to try and back flush the water passages.

All I want to do is USE this motorhome. I don't understand my luck

 

[jampants]

I messed with it a bunch today and I'm beginning to fear that something is blocking a water passage, or that a (brand new) head gasket is blown.

I messed with the air-fuel mixture and the sneezing and run-on weren't happening anymore.

I burped the cooling system again and saw no air bubbles through multiple thermostat opens/close cycles.

At idle I was seeing pretty steady temps of 180°-220° (95° day). I idled while gently revving for quite a while and everything held steady.

However, the moment I drive (on flat ground) the temps climb to the 230°-240° range.

This time no sudden spikes. Just stays hot till I shut it down so as to not do damage.

The heater air doesn't feel extremely hot. I'd guess around ~100°, which feels like a clue of some kind.

Only easy thing I can think to try at this point is to temporarily remove the thermostat to rule out it restricting flow.

I think if that doesn't change the situation I'm going to have to start taking things apart to try and back flush the water passages.

All I want to do is USE this motorhome. I don't understand my luck

Have you tried speaking to S&J? They should have done some testing before shipping it to you - maybe they can give some insight also.

I used Claude AI to help diagnose some transmission issues and while it was useful to get some ideas it is definitely over confident at times (assume chatgpt is the same) - it can sometimes send you down wrong diagnostic paths while its adamant its correct, until its not and then declares a whole new path to look into overly confidently.

Hope you get your issues sorted soon. Feel you on the sometimes endless issues train.

 

[Kelpiesgmc]

For my work I use Claude and ChatGPT a lot and I've learned to be highly skeptical about what they say. I've seen them be confidently wrong more times than I can count.

Calling S&J is a good idea. I'll do that this week. Though I imagine they will say the water passages were fine when they tested them. If anything is blocking them it's probably some Permatex I used on a gasket.

So I was thinking. If it is a bit of gasket sealant or debris of some kind couldn't I remove the water pump, hook up some high pressure water to the port at the top of the intake manifold where the T threads in (the one that feed the water heater pre-heater) and try to blast the blockage out the front two ports?

 

[jampants]

For my work I use Claude and ChatGPT a lot and I've learned to be highly skeptical about what they say. I've seen them be confidently wrong more times than I can count.

Calling S&J is a good idea. I'll do that this week. Though I imagine they will say the water passages were fine when they tested them. If anything is blocking them it's probably some Permatex I used on a gasket.

So I was thinking. If it is a bit of gasket sealant or debris of some kind couldn't I remove the water pump, hook up some high pressure water to the port at the top of the intake manifold where the T threads in (the one that feed the water heater pre-heater) and try to blast the blockage out the front two ports?

Maybe a coolant pressure test could help - to see if you get any odd readings from that in terms of fluctuations while increasing the pressure

You said you didn't have any leaks but if it truly is blocked somewhere that might do something. The coolant test kits are super cheap on Amazon and very quick to use.

Or just a coolant flush and some coolant pressure pumping to see if anything comes out if you disconnect the bottom heater hose.

Or a super purge as you suggest.

 

[Kelpiesgmc]

I removed the water pump and pressure flushed out backwards. Seemed to get good flow. I tested the thermostat.
Put everything back together and burped the heck out of it.
Drove it around and it was a tad better, I made it many miles staying under 220°—but still after a while the heat started creeping up past 220°. Like it was slowly but steadily accumulating more heat than it was able to disperse.

As I'm burping it, you can tell when the thermostat opens because the water in the fill funnel becomes turbulent. It over flows the funnel. I have no idea if that's normal but I'm wondering if it's a sign the flow through the (brand new) radiator is obstructed or something.

 

[tmsnyder]

I removed the water pump and pressure flushed out backwards. Seemed to get good flow. I tested the thermostat.
Put everything back together and burped the heck out of it.
Drove it around and it was a tad better, I made it many miles staying under 220°—but still after a while the heat started creeping up past 220°. Like it was slowly but steadily accumulating more heat than it was able to disperse.

As I'm burping it, you can tell when the thermostat opens because the water in the fill funnel becomes turbulent. It over flows the funnel. I have no idea if that's normal but I'm wondering if it's a sign the flow through the (brand new) radiator is obstructed or something.

Do you have a part number for the water pump?