Community Forums

tgenardi · 08-02-2022, 04:02 PM

Hello,
We own a 2005 Tiffin Allegro Bus, 400 cummings. Is OK until we start an incline and it overheats. I just replaced the 180 thermostat because I thought maybe it was sticking and added 6 gallons of coolant over the last few days. I'm not finding any leaks, but it runs around 200-250. Coming over Vail and Eisenhower passes this weekend, I had to pull it in 2nd gear to keep the R's up high but still had warning lights on.

I don't know if the fins are dirty and preventing airflow and I'm not sure what else could be causing the overheating.

I've read that this year Tiffin, the side radiators are too small for this size engine.

Any ideas - flush the radiator?

Any help would be appreciated.

Thank you - Tim

wolfe10 · 08-02-2022, 04:09 PM

Side or rear radiator?

Answers will be vastly different.

153stars · 08-02-2022, 06:52 PM

Does it have clutch fan ,used on rear radiators. I looked at pics could tell if rear or side radiator some have small side grill for AC condenser.
Air flow is usual suspect, but can be several causes, rear radiator is usually dirty. I believe cummins has upgraded water pump but not sure of year and engines its for, might help but not root cause.

Ghughett · 08-02-2022, 08:37 PM

Quote:

Originally Posted by tgenardi

Hello,
We own a 2005 Tiffin Allegro Bus, 400 cummings. Is OK until we start an incline and it overheats. I just replaced the 180 thermostat because I thought maybe it was sticking and added 6 gallons of coolant over the last few days. I'm not finding any leaks, but it runs around 200-250. Coming over Vail and Eisenhower passes this weekend, I had to pull it in 2nd gear to keep the R's up high but still had warning lights on.

I don't know if the fins are dirty and preventing airflow and I'm not sure what else could be causing the overheating.

I've read that this year Tiffin, the side radiators are too small for this size engine.

Any ideas - flush the radiator?

Any help would be appreciated.

Thank you - Tim

Last year we had a coolant leak but didn't see any signs of where it was leaking, to keep a long story short is was leaking into the exhaust sytem, found out it was a bad cylinder head and had it replaced. 2015 Phaeton with a smaller cummings. It didn't blow white smoke or showed any mechanical problems other than the loss of coolant. There was another concern that the coolant may of been leaking into the egr valve, but we didn't get that lucky. Good Luck

Mandalayman · 08-02-2022, 09:57 PM

I have a 2005 400 ISL side draft radiator also and have found that Freightliner installed undersized radiators in those years. I've had new coolant, cleaned the radiator stack. CAC is good and no leaks. I had the ECM replaced and reprogrammed as it wasn't telling the hydraulic pump fan to speed up when more air flow was needed. I was told to help cool it just keep the RPMS at 2000 and turn on the heater flow control to get that extra cooling with the heater core and long hoses and it did help. Lastly most heat problems have been when the outside temperature is in the 90's low 100's
I thought that there might be a larger transmission cooler available but nothing.

Bruce Anthon · 08-03-2022, 05:25 AM

When you say you didn’t find any leaks, was it just looking for coolant on the ground or have you pressure tested the system? If it holds pressure, then I would replace the cap and clean the outside fins. You will be surprised how much dirt gets in the fins between the radiator, cac and the transmission cooler. Simple green extreme is recommended for the aluminum fins.

If it doesn’t hold sustained pressure it will be internal. Have you pulled the oil dip stick and checked for coolant there? Good luck on narrowing it down.

Country Road · 08-03-2022, 07:12 PM

Yes, time to get it pressure checked before you ruin your engine. Sounds like a head gasket since you see no external leaks. The engine temperature is rising when the coolant gets low and this is very noticeable with higher outside temps.

n2zon · 08-04-2022, 01:08 PM

We have a 2006, which is essentially the same as your '05. We went up Vail and Eisenhower on cruise control this Spring, and had no problem keeping up with the trucks with no temperature issues.

I would check the wax valve or fan controller for the hydraulic fan motor and the radiator cap. If I recall correctly, Cummins uses a 15-lbs cap, so it should hold coolant up to something like 250F.

tgenardi · 08-07-2022, 01:48 PM

Thank you all for your input.
This is a side radiator and I had also put on a new cap on when I replaced thermostat.
I’ll be taking the rig to truck stop this week to get radiator power washed and we’ll see what happens from there.

I’ll let you know if it helps.

Thanks again

Tim

Gary RVRoamer · 08-07-2022, 02:12 PM

The thermostat isn't the temperature controller on a big diesel chassis - it is there merely to speed warm-up and opens wide at about 160. The fan is controlled by the ECM as needed to prevent overheating, but generally diesels run best at the upper end of its temperature range. Therefore Cummins ISL diesels are allowed to run anywhere between about 180 and 206. Above 206 the ECM starts managing the temperature back down a bit.

Side radiator model chassis from FCCC are equipped with a variable-speed hydraulic fan. It runs at a low speed to provide basic cooling for the radiator, a/c condensor and CAC and the ECM kicks it up to a high speed if the coolant temp climbs to around 206. At the higher speed it should be able to hold under 210 or even pull the temp down to around 190. If yours cannot, there is likely a fan control fault or a problem with the fan itself. The failure mode for the fan control is supposed to be full on (highest speed), which results in low temperatures rather than high. It could also be a failing water pump not circulating enough coolant.

You say you had to add 6 gallons of coolant in just a few days but don't find any leak? Yikes! It has to be going somewhere! If not outside the engine, could it be leaking into the cylinders and crankcase? Have you checked the oil?

rvspec · 08-07-2022, 02:49 PM

I'm not sure if you have fan controller or not. The older Spartan chassis did not .If it doesn't you hear the fan all the time even when the engine is cold. If you don't hear the fan the motor is probably bad. if it has a fan controller and you disconnect the wiring from it it should put the fan in the high mode. My Allegro bus will run hot if you just let the cruise control handle the shift. best to down shift and keep the RPM between 1800-2000 Don't let the temp get over 210.