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Engine Temp Too Cool?
We drove about 2 hours Wednesday mid-day and about 90 minutes Saturday late morning. Ambient temperatures were 50-60 degrees each day. Both drives included a mix of interstate, state highways and town driving.
However, the engine did not come up to normal operating temperature. One time Wednesday on the interstate the engine temperature rose close to 190 but the rest of the time it ran about 180 or a shade less. The engine and transmission temperatures are tracking together.
I thought the radiator fan might be stuck on high but it seems to be functioning normally.
What is going on?
I have 400 miles to drive next Saturday so I need to address this if it is problem. I am a few miles west of Foley, Alabama this week.
Thank you.
Davy
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25 Replies
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Gas engines have a thermostat to regulate heat of the radiator. If it’s haywire a number of things can happen from no heat from the heater, to overheating or under-heating.
I don’t know if a diesel has the same thing but If it does and it’s a very easy and inexpensive fix.
Harry
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Davy,
When the engine is started does the fan free wheel? It may rotate a little, but not as if the clutch was engaged.
From your description of temps it sounds as if the temps are cycling on the thermostat and that the fan is locked at low speed.
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I will check that, Jon. I guess I assumed the low was the starting position for the fan.
Davy
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Until your engine is around 204 degrees the low speed fan will not kick in and the fan may rotate a little but it will not be driven. In fact from a cold start even on high idle it is difficult to get the engine temp high enough within a reasonable time period to see fan engagement.
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Thanks for that.
Would a fan running on low keep the temps down to 180 when running down the highway? I can not imagine that. My normal is 195-200. It has always went up to those temps a few minutes after beginning to actually move. It is hard to pinpoint in the XL gauges.
Davy
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Davy, just a guess, how bout the gauge, ground, sending unit?
Many years ago, my exhaust temp gauge began to show lower temps gradually, and now shows no temp. Put in a new pyrometer – no help. Still don’t know what’s up.
So I don’t know where our gauge grounds are located.
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Could that affect both the coolant temp gauge and the transmission temp gauge? They are tracking closely together. I believe it is showing me the real temperature.
I am open to the possibility.
Davy
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It sounds to me that one of your two coolant thermostats on the engine is stuck open. This would not allow your coolant to come up to full operating temperature under normal operation.
Item 1 are thermostats. Item 9 the seals.
I don’t think your issue is related to the fan operation. Even if the fan was on high all the time the coolant should come up to temp since the thermostats when functioning properly would not open until the coolant is at temp.
Gerald
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Thank you. If that is so, then I suppose it could easily stick closed with the opposite affect. Where are the thermostats?
Davy
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Davy,
I had a clutch fail on a trip once so I had to lock the fan so I could complete the trip. I don’t remember seeing temps as low as 180, but I do remember it cycled what appeared on a poorly marked gauge around 185 to 195 and when I checked after the fact that seemed to be the thermostat range.
A locked clutch is going to bring in so much air you will need to have the thermostat close just to keep the engine warm. With even the low speed locked unless you are ascending some long steep hills the engine will still run cool.
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The stats are located at about the 11:00 position if you can imagine that the engine is round and your standing behind the bus looking into the engine bay.
Another guess: maybe the fan is electronically locked due to a failed relay, although I’ve never heard of this happening. To test, turn ignition key on, do not spin the Detroit, OTR off, grab the fan by hand and turn it. If yes = ok, if no, not ok.
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Davy, yes the T-Stats are on the same side of the engine as the fan…tucked tight to the engine, you must remove several hoses and the coolant to change them out…
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Thank you all for the information. The diagram was helpful, Gerald.
Here are the answers to two things I was asked.
With the key on, engine off, the fan spins easily by hand.
Once the engine was cranked, and the belts had tension, the fan immediately kicked on, no doubt about it. It is being driven right from the start. contrary to what it is supposed to do.
What do these things tell me?
Davy
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Kyle Bennett (Service)
Brian Miller (Sales) -
Davy,
Just for grins because it is easy and cheap replace the fan clutch relays (78/79?) with known good ones and see what happens.
If nothing has changed you can rule them out and then find out why one of the relays is getting a signal to engage the clutch. It could be a sensor problem or maybe DDEC is thinking the temp needs the fan engaged.
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Thanks, Jon.
I just “happen” to have 8-10 spare 24v relays including one with blade 85 removed so I can lock the fan in high speed if absolutely necessary.
I checked the diagram to make doubly sure of the correct relays, replaced them and no change. The fan is immediately driven upon the bus cranking.
Now, what calls for the fan to be on? You mentioned sensors? The computer? Can a stuck thermostat play a role in this with the engine completely cold? What do I do next?
Davy
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