Strange cooling issue

[Bryantclan]

Hello all,


I have run in to a strange cooling issue with my 2007 AllStar.

We do allot of trips in lower temps over the winter, mostly transiting out of denver west for the holidays. During the last trip anytime the outside temp was between 24 and 40 the engine temp bounced between 150 and 235, every 2 minutes or so. What it looks like is happening is the thermostat is closing, the engine temp then starts to rise over the 2 minutes in which case it opens and the temp drops in about a second. And does this over and over again regardless of load. Above 40 and below 24 the temp stays steady.

Any ideas would be great... Thanks.

[BFlinn181]

If all wire connections to the temp sensor and dash gauge are clean and it's working properly, I'd say a new thermostat is the solution. It should close at 150, that's still 'cold' and open at 235, that's a bit above normal. The drastic change could be from the colder radiator coolant then flowing into the engine. If the thermostat is partially blocked or sticking, it could create the issue you described.

[Lug_Nut]

I think I would first verify that the gauge is operating correctly. Do a gauge check on the diagnose menu. It will cycle all the gauges. Watch the heat one closely and compare how it reacts compared to the others. The 235 is way too hot.
Thermostat, possible, heat sender may be, fan control also possible.

Peter

[Bryantclan]

I am seeing the same thing happen on the VMSpc so I am reasonable sure it is a good read.

Would a sticking thermostat happy work outside of a region of temperatures?

[Lug_Nut]

It certainly is strange, given the narrow window it only occurs in. Any chance your coolant level is low? Thermostat is a cheap relatively easy fix, if that solves it.

Peter

[palehorse89]

Originally Posted by Lug_Nut

Do a gauge check on the diagnose menu. It will cycle all the gauges.

Peter

Peter, can you tell me how this guage test is done?

[Lug_Nut]

The newer coaches have an information bar that allows this to be done within the light bar, but your, a 2000, probably has the gauge check immediately upon turning on the ignition key. It will light all warnings under each gauge and may cycle all readings to full scale and back to zero scale.
The light bar information center can be ran in manual mode or automatic. The poster's '07 probably has the info bar.

Peter

[palehorse89]

Yes you are correct about my setup Peter, Thanks for the reply.

[Bryantclan]

To follow up on this, went by cummins today, it seems that when I had the thermostat replaced last year the service tech decided he did not like the ECU settings for the cooling system and made some changes..

[palehorse89]

Did they tell you just what he did, your coolant temp. should not fluxulate that much, the engine should get to thermostat temp and hold close to that temp. kinda sounds like you thermostat is not working right ( maintaining proper coolant temp.) What did they change in the ECM that would cause these temp. swings?

[Iron Man]

The guage gets its information from the ECM as does vmspec, so unless the guage itself it is something else. I had a similiar issue turned out to be a bad thermostat gasket that allowed coolant to bypass the thermostat.