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 > Diesel engine thermostat operation

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wagonmaster2

northcentral oklahoma

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Posted: 10/27/08 09:47pm Link  |  Print  |  Notify Moderator

I have a 4 year old Cat C-7 engine that will only reach 194-197 degrees when pulling hard on a very warm day. Cruising down the highway on a cool day, 50-60 degrees outside, the engine temperature will usually take an hour's driving to reach 160-167 degrees and stay there most of the day if the outside temp stays the same. Most car engines with 195 degree thermostat will reach that temperature in just a few minutes driving and stay about that all day, whether a hot or cool day. Is my diesel operating as it should or is one or both (at least I've read they have two) of the thermostats frozen open? Its done this since day one when it was new. I know the recommendation is to change the thermostats every 3 years but if this is the way they should operate I didn't want to risk changing things for the worse. Maybe I shouldn't complain since I've read so many cases of diesels running hot. Any ideas?
Wagonmaster2

1MTNEST

St. Albert, Alberta

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Posted: 10/27/08 10:29pm Link  |  Print  |  Notify Moderator

I have a 400 Cummins that runs at 185 all day long. On a hill climb on a hot day ( climbing from Phoenix to Flagstaff ) it will only come up 5 degrees.
Not sure what Cats run at but you could check their web site for tech issues.


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w4phj

Vero Beach, FL

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Posted: 10/28/08 06:43am Link  |  Print  |  Notify Moderator

urmine351 wrote:

My C-7 runs at 176


My C-7 runs at 176 also. It quickly reaches this temp and stays there.


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J Walker

Oakton, Va

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Posted: 10/28/08 08:03am Link  |  Print  |  Notify Moderator

Your thermostat is definitely stuck open. I have a Silverleaf engine monitor which is much more accurate that the dash gauge and my engine quickly reaches 180 degrees and then ranges between 180 and 190. You will lose some efficiency with the engine running cool and maybe even damage due to fuel washing down the oil in the cylinders. I would not delay getting this fixed.


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Posted: 10/27/08 10:34pm Link  |  Print  |  Notify Moderator

wagonmaster2 wrote:

I have a 4 year old Cat C-7 engine that will only reach 194-197 degrees when pulling hard on a very warm day. Cruising down the highway on a cool day, 50-60 degrees outside, the engine temperature will usually take an hour's driving to reach 160-167 degrees and stay there most of the day if the outside temp stays the same. Most car engines with 195 degree thermostat will reach that temperature in just a few minutes driving and stay about that all day, whether a hot or cool day. Is my diesel operating as it should or is one or both (at least I've read they have two) of the thermostats frozen open? Its done this since day one when it was new. I know the recommendation is to change the thermostats every 3 years but if this is the way they should operate I didn't want to risk changing things for the worse. Maybe I shouldn't complain since I've read so many cases of diesels running hot. Any ideas?
Wagonmaster2


My C-7 runs at 195 always....sounds to me like the thermostat is stuck open....





urmine351

fort smith, arkansas

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Posted: 10/28/08 06:27am Link  |  Print  |  Notify Moderator

My C-7 runs at 176


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Posted: 10/28/08 08:47am Link  |  Print  |  Notify Moderator

I had a 3126b Cat (C7) in a 2000 Safari that would overheat on long hills or in temps over 110 at highway speeds. There was no real fix for this other than a larger radiator that Safari later put in the coaches. They did what they called a "heat" kit that was a set of louvered doors, a duct shroud around the fan a new nine blade fan and a smaller pulley to run the fan faster.
The Cat had two thermostats as I recall so perhaps one of them is stuck oen. I'd suggest you get it into a Cat service dealer to find out.

J Walker

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Posted: 10/28/08 02:55pm Link  |  Print  |  Notify Moderator

I can't believe what I am reading in this thread! First, don't report what your dash gauge says as a temperature. A digital readout is what I am reporting. In any case you could call CAT help line and clear up any questions. My Cummins has one thermostat and I can't imagine a diesel engine without one.

wny_pat

Western NYS

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Posted: 10/28/08 08:53am Link  |  Print  |  Notify Moderator

50pascals wrote:

I wouldn't rush to say it's a thermostat.

"diesel trucks don't act like cars in that regard - there's not enough waste heat at idle or low load."

There's always enough heat to keep the cab comfy and all, but he suggests covering the radiator - I have a FRED. Maybe a pusher wouldn't be as susceptible in the winter.

There's your answer, except I will not agree with the last paragraph applying to all diesels. I have driven over the road tractors which would not keep you warm and comfy when not pulling a load when the ambient temperature is 10 degrees f or below. They were okay when pulling a load. Diesels are cold blooded generally speaking.

I don't know how the Cat is set up with a thermostat. Many Cummins do not have a thermostat persay. Their water pump controls the heat by controling which way the coolant flows in the system. My suggestion would be to find a good Cat mechanic to check the system for proper temperatures. Dash temp gauges can be very off and not dependable.

* This post was edited 10/28/08 09:02am by wny_pat *


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50pascals

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Posted: 10/28/08 08:40am Link  |  Print  |  Notify Moderator

I wouldn't rush to say it's a thermostat.

I have 2 Cummins 5.9's. One in an F-800 and one in the motorhome. Both do the exact same thing, even with new thermostats - multiple thermostats (a seperate issue).

Many times the MoHo is operating just into the warmed up zone.

The F-800 will sometimes in winter run quite cool - especially because we have to idle it all day for the pto drive. We completely block the radiator with cardboard.

Truck shop says normal, and "diesel trucks don't act like cars in that regard - there's not enough waste heat at idle or low load."

There's always enough heat to keep the cab comfy and all, but he suggests covering the radiator - I have a FRED. Maybe a pusher wouldn't be as susceptible in the winter.

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