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Engine Cooling On CAT 3126B Engine


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#1 sdlmkr

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Posted 03 September 2013 - 01:34 PM

On  a recent trip the cooling fan fell of my Cat 3126b motor.  There was no damage other than to the fan.  I had a diesel shop put a new fan on.  On my way home (80 miles from the shop, the coach heated up and the check engine light came on.  I pulled over and let the coach idle for a while and the light went off.  I then changed both thermostats thinking that the high temp that was caused when the fan fell of might have affect the thermostat performance. 

 

After completing this task I took the coach for a run for about 30 miles where there was a somewhat steep grade.  The coach overheated and the check engine light went on briefly then off...outside temp was around 89-90 degrees F.  The coach cooled somewhat back to home but maintained a temp about 195-200 (thermostats are 190).  The fan blade is the same as the one that came off.  Mechanic doesn't know what is going on. 

 

He suggested that the high temp that resulted when fan came off could have affected the water pump saying the high temP could cause the impeller to expand on the shaft, and cooling it off would engage it again but if it gets up to temp it might slip.  My question is has anyone ever heard of this happening to a water pump?

 

Any other suggestions of what might cause the overheating would be appreciated....in 4 years I have never had any overheating problems, steep grades in Idaho, hot day pulling toad, etc.

 

2000 Cat 3126B engine, Magnum chassis, Allison 6 speed trans, coach was made by Harney, now has 38,000 miles.

 

Thanks for any help.....

 

Phil


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#2 wolfe10

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Posted 03 September 2013 - 04:54 PM

Phil,

 

Welcome to the FMCA Forum.

 

Since this occurred starting when the fan was replaced, first thing is to verify that the fan is the correct one AND that it is installed with the blades facing the proper way.

 

Can overheating affect the water pump impeller/shaft-- yes.

 

But several other things I would do before replacing the water pump.

 

Assume that when you installed the thermostats that you either bled the air from the thermostat housing or as is common on many chassis that there is a bleed line from housing to overflow reservoir.  An air pocket can cause the thermostats to not open properly.

 

Also, you did not mention cleaning the CAC (charge air cooler) and radiator every year.  Most of the dirt and debris will be on the front of the CAC.  You can check with (best after dark) with a strong flashlight from the bedroom.  Look inside the fan shroud/between fan blades.  Verify that the perimeter, particularly the lower perimeter is as clean as the center (the fan blades sling the dirt to the perimeter.

 

Also, as a PM item, make sure the crankcase breather hose (open 1" ID hose on passenger's side middle of the engine has been extended to behind the fan shroud.  If not, oil vapor and water vapor from the engine can be sucked up into the cooling package and materially speed its clogging.

 

Brett


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#3 DickandLois

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Posted 03 September 2013 - 05:07 PM

 sdlmrk, Welcome to FMCA,

Do you know how hot the cooling system got after the fan foaled ?

 

The temperature required to cause the failure the mechanic mentioned should be much higher then an engine would reach and still funtion.

 

The one item that come to mind is that when the fan failed the cooling temperature was high enough to cause steam to form in the system, leaving behind an air pocket at could be causing a water pump cavitation. 

When your engine over heats do you get hot air out of the heater?

 

Rich 


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#4 sdlmkr

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Posted 03 September 2013 - 10:13 PM

Brett and Rich...thanks for your quick response to my questions.

 

Brett...I checked with the mechanic today and he said he ordered the new fan blade using the number stamped on the old one, and checked the number on the old one against the new one and they were the same.  Both are 7 blade fans.  I read earlier where alot of the MH's with CAT 3126 B engines and 300 hp were using 9 blade fan blades.  I checked the air flow thru the CAC and radiator at the back of the MH with a paper towel and the air did blow the paper towel out away from the radiator but not with any abundance of pressure.  I suspected the fan may have been put in back wards but I'm not really sure how to tell just looking at the fan?

 

There is a bleed line the thermostat housing and I actually unhooked it and let antifreeze come out so I was sure there wasn't an air pocket.

 

I sorta gave the CAC and radiator a clean bill of health because we left our ranch here in Idaho pulling our Harley trailer behind and made a trip over to Yellowstone park.  There were lots of fairly steep grades and the MH never overheated one bit nor did the transmission.  In fact in the 4 years I've owned this coach pulling the trailer or a car I've never had any overheating problem.  I'll probably do a cleaning job on both once I get the fan direction put to bed for sure. The breather hose had been extended beyond the fan shroud as you suggested.

 

Rich..I didn't hear any noises when the fan failed and first noticed a problem when the check engine light came on...at that point I'd say the water temp was over the 190 mark and the tranny was also.  I pulled off the road, let the engine idle and went to the back of the coach where I heard a high pitch squeal....I shut the coach off and look down thru the bedroom hatch and saw the fan mechanism laying on the bottom of the shroud.  I believe looking back now that the water temp was around 235 or a little more when I shut the coach off and trans. temp was about that high also.

 

I failed to mention that on the first run after the thermostat installation the ambient temp was around 88-90 degrees.  The next morning when it was cooler ambient temp (60-65) I did the same run and the water temp went up to just over 190, maybe 192 but never did go high enough to trigger the check engine light.  Then on the way back home I did some experimenting like going into 5th gear from 6th and gaining some rpm's and noticed some affect in the cooling...temp went down just a degree or two..I did this at a couple different speeds 55 and 65 and found the with the higher rpms at 55 I got a little more cooling than at 65.  These little tests is what turned me back to the possibility of a fan problem. 

 

I haven't paid attention to the heater when the engine is overheating but I will tomorrow.

 

Thanks so much to both of you....if anything new comes to mind I will appreciate anything you guys want to offer.


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#5 kaypsmith

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Posted 03 September 2013 - 10:31 PM

Just one quick little thought, the fan when running should be pulling from the outside in to the radiator. If this is happening, then the direction is correct. Also, if when coming off, the fan may have damaged the shroud, a hole in it will cause overheat.

Good luck,

Kay


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#6 wolfe10

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Posted 04 September 2013 - 06:59 AM

Kay,

 

That is INCORRECT.  Air is sucked in from the front of the shroud and the fan forces air out the back-- through the CAC and then through the radiator. 

 

At highway speeds, it would be virtually impossible to use the back, which is in a high vacuum condition, as an intake source.

 

 

sdlmrk,

 

Take a picture of the fan blade in the shroud and post it.  Someone else with a Safari/Magnum chassis (suspect that is what you have-- let us know) can look at it and compare with how theirs is orientated.


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#7 sdlmkr

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Posted 04 September 2013 - 04:12 PM

Brett...here is a pic of the fan in my MH.  Rich was kind enough to send me a pic of a fan he had in the same position as my fan.  I noticed on his the convex side was pointing towards the engine, where as on mine the concave side is pointed towards the engine.  Which makes me think mine is in backwards.


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#8 wolfe10

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Posted 04 September 2013 - 04:50 PM

Sorry, no picture visible. And, it will be the Sunday before I have access to the fan on our Safari coach.


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#9 sdlmkr

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Posted 07 September 2013 - 11:13 AM

I'm here to report the progress on my overheating problem after a repair on the cooling fan.  With the help of FMCA members Rich and Brett I was able to finally figure out my problem....the fan was installed backwards.  Rich sent a picture of a fan in the correct position for installation on a pusher motorhome.  I could easily see that mine was in the wrong position.  I have a CAT 3126 B engine and the air flow is from the engine to the back of the coach thru the CAC then radiator and out the back of the coach.  For future reference when you look at the fan from the front (side closest to engine) you should see the convex side of the blades .....mine was installed with the concave side exposed....

 

Concave is curving in or bulging inward and Convex is curving out or bulging outward


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#10 wolfe10

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Posted 07 September 2013 - 11:40 AM

Excellent. Sure an inexpensive "fix".

 

Brett


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