Coolant thermostat

[Paul Schwalen]

Hi all,

I experienced  temperature spikes yesterday while driving on level roads in Louisiana.  I typically keep an eye on the Alladin screen while on a trip and noticed that the engine temp and transmission temps went up about 6 degrees fairly quick and I became concerned and watched to see if they would start down again. (typically while climbing a grade the engine temp will slowly rise and then slowly come back to its usual 180 deg)  This time is was on level ground and doing my typical 57 MPH and after it rose it did not start to drop and I slowed down and was able to pull over. I found the surge tank almost full and have never seen this happen before.  I shut down and looked for leaks or other causes and could not see any, started up again and the level in the tank went back to normal after a few minutes, with no other spikes along my route.

Can anyone suggest what may have caused this?  Could it be a faulty thermostat?  Any thoughts?

Thanks,

Paul

[Robert Mathis]

I doubt it was the thermostat, once they fail, they don't usually start working again. I can't imagine it would be open. close and re-open again. Do you know the temperature it is supposed to open? Mine opens at 185, and the engine runs about 188-195 depending on speed and load. I make a habit of watching the Alladdin during warmup to make sure it opens and the temps fall and then recover.

[Tom and Pam Brown]

Paul, had a similar issue last trip.  When I inspected the radiator and charge air cooler I found a lot of grass clippings I had picked up somewhere.

Rose about 2-4 degrees above normal.  I blew the clippings out and returned to normal.  So take a look and make sure you have not sucked something in your radiator area.

[Joel Weiss]

I don't know about Cummins engines, but on CAT's the thermostat is a 3-yr replaceable item.  I decided to have mine replaced last spring even though I was not aware of any problems.  I was amazed by the changes I saw after doing so.  Previously, the thermostat would open and the engine would run ~185-190 with an occasional excursion up to 200 with heavy load.  Now using the SilverLeaf I can see the thermostat actively trying to keep the engine temp between 190-195.  It will close a bit and let the temp get as high as 196 then it will open somewhat until the engine reaches 185 then the cycle will repeat. On steep grades throughout the summer the max temp has not gone beyond 199 even momentarily.  

I can't directly this change in behavior to better performance or fuel economy, but I would think that the engine running slightly warmer would improve both very slightly.  

[Paul Schwalen]

Joel, - Thanks for the comment - I am pretty sure my thermostat is the original.  I hope others can chime in with any experience on a thermostat being intermittent.

Tom, - Thanks for the thought - I checked for debris on the face of the radiator and it seems clear.

Robert, -  I seem to remember reading somewhere about thermostats acting funny.  Hope this is the problem with mine.

Thanks,

Paul

[Dennis Crawford]

Paul,

ON my Cat, the engine runs about 190 degrees.  When it reaches the thermostate temp of 192, it will open and the temp may drop as low as 188.

Have you checked your cooling fan?  Was it coming on properly?  If yours is a side mount and is hydraulic, I know there was an issue with the Alison PTO that drives that fan.

Dennis

[Paul Schwalen]

Dennis,

Thanks for the reply, we are parked for a week and I think the only way to check the fan (we do have a side radiator) is to have the engine up to temp.  I did check the hydraulic fluid level and it is possible it is down some.  The problem is when we are home the level is seen thru the sight glass but when home the rear of the coach is low so I think the level may be OK but won't know until we arrive home.  I am uncertain if I should add a couple quarts or wait.  I see no evidence of a leak and think I will probably wait till I get home and see where the level is.

I still hope someone will chime in on the possibility of the thermostat having an intermittent problem.

Paul

[Edward Buker]

Paul,

Having driven your coach for awhile and having watched the Alladin you know what is normal for your temperature range. That being said an excursion of only 6 degrees does not seem serious to me especially at only 186 degrees as a high. You may pick 57mph for mileage reasons and may be running just into 6th at low RPM which can limit the fan drive available power. Not sure what the outside temp was and if you were on a mild grade that was hard to detect. If this happens again you could try dropping down a gear and if the temp drops it is not your thermostat, just limited fan cooling. Tom mentioned cleaning the radiator which certainly may also be a possibility. If this is really abnormal and you are worried you could have the thermostat replaced as a precaution but before you do ask what the upper temp limit is supposed to be before you worry too much. It should be up in the 200s, well above this range that you are worried about. It is normal for things to cool at idle with no load on when you restarted so things looked like they were acting normally at that point.

Under extreme conditions I have peaked at 205 degrees with a 505hp version of a C12. Usually I run with very stable temperatures in the 188 range but as you can see some excursions are expected...

Later Ed

[Steve Huber Co-Admin]

Paul,
Ed is correct re slight elevation changes impacting engine temp. I use a GPS that gives ongoing elevation. The effect of even a slight climb can cause a temp increase. Increasing engine RPM to get fan speed and the water pump rotating faster is more effective in cooling the engine than slowing down, which decreases coolant flow. My previous Contessa with a 3126 would normally run at 194 but would add 2-5 degrees fairly quickly when climbing slight grades that were pretty undetectable to the eye. My current C12 runs cooler but exhibits similar behavior on slightly steep or longer grades.
Steve

[Gerald Farris]

Paul,
There is a possibility that the thermostat caused the very slight temperature rise that you saw, but there are many other possibilities as well. I would personally completely disregard the event as I am sure that any good shop will also. Something that minor that that does not have a repeatable pattern is almost impossible to diagnose without wasting a ton of $$$.

Gerald

[Paul Schwalen]

Thanks Ed, Steve and Gerald,

All good points taken.  I am a bit of a worry wart when it comes to temps and would not have been as excited if the transmission temp had not risen along with the engine temp.  I follow the forum all the time and always worry about the transmission cooler failing and losing the Allison like happened to Tim some months ago.  My Contessa is now 10+ yrs old and I have the usual running temps on the dash above the Alladin and was concerned when they rose.  As Ed noted a gradual rise is hard to discern but this is Louisiana and I-12 like most of the state is flat.

I will do some research on the default temp for the stat to open just to have that info for the trip home next week.  

Paul

[Mike Merchant]

OK gents, you've got me thinking, which may be a dangerous situation.
Or '06 Monty always ran 188-192, with rise to 200-202 on steep grades. Got the '09 Contessa in 2011 and noticed it ran at 201-203,with the Allison also running that temp. Seems happy, rises over about 30 minutes on the road and stays in that range. Has risen to 210 -212 coming up the grade from Panamint Springs, Death Valley (below sealevel) to Towne Pass (5000') in about 12 miles, with the tow, WOT and in 2nd gear for last 1-2 miles.
Going in for routine LOF at a Cat authorized shop in a few days. It's coming into it's fifth year, should I have them change the thermostat as per JW? Any other thoughts or am I just another worried well?

                                                                                                                                                                              Mike

[Paul Schwalen]

Hi all,

I  talked to Cummins and  the thermostat opens at 180 deg.  The tech also told me the stat should last hundreds of thousands of miles and he has never heard of one that is intermittent.

I will know more when we drive home next week.

Thanks all for the comments, etc.

Paul

[Edward Buker]

Mike,

The thermostats remain in a friendly environment from a corrosion and wear viewpoint. I sold my 20 year old Contessa and it still had the original thermostat in it without issues. My current Marquis has a 12 year old thermostat in it and I for one am not concerned given the very low failure rate of this component. Our miles driven are minimal compared to commercial applications that over the road long haul trucks experience that the components are engineered to survive.

You have about a 10 degree rise between normal and heavy load use which is quite normal. Personally, I would not change it unless it is supposed to be a 185 or 195 degree thermostat that is running hot. If it is supposed to run at 200 degrees by design, and that is normal for your engine, then you should be fine. That question is worth asking.

Later Ed

[Mike Merchant]

Ed,

Thanks for the info. They hopefully can pull up all the technical data on my C9 when they have the serial number. I'll ask.

                                                                                                                             Mike