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engine overheating

2003 U295 Cummins 400 ISL
Showing no loss of coolant.

On recent trip with temps in the mid-90s, started trip at 180 degree engine temp. Then, after about 100 miles temp rose to 206 and stayed there for about 30 miles. It then went to 212 and I pulled over for about 15 minutes and temp started coming down so I continued trip eventually going down to 180 and staying there for another 50 miles and then the cycle repeated.  The cycle continued on way home. For the most part, there was not much change in elevation. Normally this trip would have run between 180-185 degrees. Did not lose any coolant over the whole trip.
Does any of this make sense? The controller for the coolant system fans has been suggested as the culprit.                Thanks, Ron

Re: engine overheating

Reply #1 –
Quote from: Dakota Slim –
What were the roads like, grade wise?
(Oops. Sorry, I missed that part of your post.)

Yes, was the coolant temperature change due to understandable factors?

Also, when this occurred, were the other dash gauges reading normally or did they also read abnormally?

If not explainable, first thing I would do is change the thermostat.  They can hang up and not open/close properly.

Re: engine overheating

Reply #2 –
Quote from: graybill1 –
2003 U295 Cummins 400 ISL

<snip>

Does any of this make sense? The controller for the coolant system fans has been suggested as the culprit.                Thanks, Ron

Can you verify that the fans go to high when the controller in unplugged?

Cummins ISL Radiator Fan Won't Increase Speed

Hopefully Jim can jump in with some guidance as well, since he fought a similar issue and recently replaced his radiator after nothing else changed the behavior

What did you do to your coach today XI (2025)

Re: engine overheating

Reply #3 –
The fans go on high when the controller is disconnected, but only if at temp over 180 or so and engine has power applied. If just at normal idle, fans do not go on high.

Thanks for all responses.  Ron

Re: engine overheating

Reply #4 –
Addressing Ron's first post:

That is the way they should work-- not on high until a few degrees above thermostatically controlled temperature.

ON EDIT: Addressing what disconnecting thefan controller  does to fan speed: See post #6.

Re: engine overheating

Reply #5 –
Quote from: wolfe10 –
That is the way they should work-- not on high until a few degrees above thermostatically controlled temperature.

I'm confused.  Shouldn't the fans go to high when the controller is unplugged regardless of any other conditions?  The way I read the post, the fans would not go to high when the contoller is unplugged if the engine is at idle.

Re: engine overheating

Reply #6 –
Quote from: Geodmann –
I'm confused.  Shouldn't the fans go to high when the controller is unplugged regardless of any other conditions?  The way I read the post, the fans would not go to high when the contoller is unplugged if the engine is at idle.

Sorry if my statement was not clear.

I was describing how they should work going down the road with everything working properly-- coolant temperature should  be a few degrees above where the thermostat(s) are fully open before the fan speed goes to high.

No question, unplugging the controller should have the fans running in high.

Re: engine overheating

Reply #7 –
Quote from: Geodmann –
I'm confused.  Shouldn't the fans go to high when the controller is unplugged regardless of any other conditions?  The way I read the post, the fans would not go to high when the contoller is unplugged if the engine is at idle.

That's the way I read it as well.  It was in one of the topics I linked that the test of the controller was if the fans went to high when it was unplugged.

Quote from: wolfe10 –
That is the way they should work-- not on high until a few degrees above thermostatically controlled temperature.

Brett - in Reply #3 Ron says his fans aren't going to full with the controller unplugged - are you saying that's normal? 


See Scott's post here which indicates it might be the controller solenoid acting up

Cummins ISL Radiator Fan Won't Increase Speed

Re: engine overheating

Reply #8 –
The solenoid on the hydraulic fan controller allows full flow with no input. It requires current to activate the solenoid and slow the fan down. If you disconnect it, it will have no power and the fans will speed up. If the engine is at idle, the fans will not spin as fast as if the engine was running at 2100 rpm. The pump on the engine provides more flow at faster engine speeds.

If the fan controller is working, you should see and hear a difference in the fan speed if your engine is cold, and you unplug the controller.

It could also be a bad sensor for the controller. It uses separate sensors than the engine and the gauges. You can measure the resistance of the sensors at the plug. With the outside temperature around ~80°F - 90°F you would see about 1000 ohms of resistance on the 2 wires going to the sensors. The colder it is, the higher the resistance gets. The Foretravel side of the connector is all white wires it think. but you can use the controller side to match it up. There should be a white and black wire. That should be the coolant sensors. There should also be a black with a white stripe and brown with a white stripe. That would be the other sensor that's in the intake. You can check the resistance, and then start the engine and the resistance should drop as it warms up.

Re: engine overheating

Reply #9 –
Graybill, one thing I forgot to mention in Michelle's link is that I also removed and cleaned the trans cooler. It had an accumulation of Bars leak I was using to stop a slow leak from the radiator tank. The Bars leak was stopping up the small honey comb passages in the cooler. I'm not sure if you know of the history of what's been put in there but that is possible also. After replacing the radiator my heating issue is gone except for a few very steep climbs but I'm currently towing 9,700 lbs. and I can manage those. I had exhausted all other possibility's before replacing the radiator. If you put you're coach on high idle and disconnect the fan controller the fans will go to high speed. While engine running turn cruise control on and push the resume button the engine should increase to about 1200 rpm Jim.   

Re: engine overheating

Reply #10 –
Sorry for my confusion, for my problem, and for my lack of how to communicate easily on the Forum.

1. Could fluctuating overheating be caused by the thermostat which was replaced in January? We did a lengthy trip when ambient temperatures were all below 75 and engine temp never exceeded 185. The fluctuating overheating occurred recently on a 700 mile round-trip at altitude between 5000-6000 with no major inclines.
2. If the problem turns out to be the fan controller, is going to the wax valve system a better fix?
3.If the controller is unplugged, should the fans go to high all the time or only if rpm's are over a certain amount? Mine only go to high speed if rpm's at fast idle and not at normal idle.
4. Any problem with running all the time with fan controller unplugged if the "solves" the overheating issue?
Thanks, Ron

Re: engine overheating

Reply #11 –
Quote from: graybill1 –
3.If the controller is unplugged, should the fans go to high all the time or only if rpm's are over a certain amount? Mine only go to high speed if rpm's at fast idle and not at normal idle.
4. Any problem with running all the time with fan controller unplugged if the "solves" the overheating issue?
Thanks, Ron

#3. If the fan controller is unplugged, the fan should go to high all the time.  Yes, higher engine RPM= more fan RPM. Plug/unplug at any engine RPM and there should be significant difference.

#4. Running the fan on high all the time will (actually should) solve the overheating, but will use HP and lower MPG and, raise a lot of dust if off-pavement. The "actually should" means that fan speed is THE problem, vs thermostat, clogged CAC or radiator, bad water pump, etc.

Re: engine overheating

Reply #12 –
Our U300 Detroit looks ahead and if there is a hill, it starts to head to 200 degrees. Fortunately only in summer. So, I just pull the fan plug off in June and leave it off until the leaves are coming off the trees in Fall. I still have to turn the heater on before I get to Donner Summit. I never let it go above 200 degrees. If you have wet sleeves, this is a good maximum temp.

Even at 600 RPM idle speed, the two fans immediately go to high speed no matter if the engine is cold or up to temp as soon as the plug is pulled.

We live in the mountains where there is little flat road, only grades to go up or down and with that and the high temps we get, the Foretravel cooling system design shows it's faults.

Pierce

Re: engine overheating

Reply #13 –
Is there a reason that my fans don't go on high if the rpms aren't up and  the fan controller is unplugged? From what I'm reading, the fans should be on high when controller is unplugged even at idle.

Re: engine overheating

Reply #14 –
So the fan controller in the relaxed powered state will cause no restriction to the small control lines. As the resistance increases in the control lines the fan speed also increases. In the failed (safe) position the fans will go to hi as the restriction is already present being failed. This is the same as disconnecting the plug to de-energize the controller to induce fluid resistance. If you disconnect the fans and have no speed change lickly they are already in hi??? I you use your cruse control while parked in neutral you can increase the engine speed. Put it at say 1400 rpm and go back to the controller, with the engine cold. Disconnect the controller and you WILL notice a difference. If they are already moving masses of air and no change likely you have a failed controller. BUT this will hide a overheading issue and burn extra fuel. I drove 10000 miles before i fixed mine. So yes I did modify back to a wax valve and am happy with what I have but since smarter people than me have figured out a new design controller that I am recommending although I dont have first hand hands on experience with it. Foretravel added the electronic controller for the advantages it does have, but its dependability was poor. That being said you need to figure out if your fans are running HI or being non responsive. I literally have put a needle valve inline to the controller lines as my back up control to go home on. Valve closed = hi speed, valve open is low speed. At 1400 rpm the fans are very loud in the hi position behind the coach and are moving huge amounts of air. Siting in the drivers seat I can manually select hi-low and it is easily noticeable with the side window open. Hope this helps. Crainman recently asked if he could control the controller by removing  or controlling the power going to it and yes that will work.

Ref 2004 U320 ISM doesn't warm up for smart people

Re: engine overheating

Reply #15 –
Quote from: graybill1 –
Is there a reason that my fans don't go on high if the rpms aren't up and  the fan controller is unplugged? From what I'm reading, the fans should be on high when controller is unplugged even at idle.
Possible difference in models or years? Perhaps yours is already in high speed with low speed not working?

P

Re: engine overheating

Reply #16 –
more confusuion:
Took the motorhome for a test drive today with the cooling fans unplugged. The overheating seemed to stay under control, but on one slight incline, the temp rose to about 185, but then on the downhill side, pretty much coasting, the temp rose to 192. Once under acceleration again it quickly dropped to around 180 which is normal.
Any possible explanation for the rise in temp going downhill?
Thanks, again. Ron

Re: engine overheating

Reply #17 –
A guess is that going downhill your engine rpms are down. Pump speed would be down too. Possibly test again with transmission in a lower gear going down the hill.

Re: engine overheating

Reply #18 –
Quote from: graybill1 –
more confusuion:
Took the motorhome for a test drive today with the cooling fans unplugged. The overheating seemed to stay under control, but on one slight incline, the temp rose to about 185, but then on the downhill side, pretty much coasting, the temp rose to 192. Once under acceleration again it quickly dropped to around 180 which is normal.
Any possible explanation for the rise in temp going downhill?
Thanks, again. Ron
Was the retarder on going down the hill?

Re: engine overheating

Reply #19 –
Retarder was on and probably was being used since there's a stop sign at bottom of hill.