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I have a 2007 Peterbilt 387 with a C 15 Cat engine. I noticed…

I have a 2007 Peterbilt...
I have a 2007 Peterbilt 387 with a C 15 Cat engine. I noticed my oil pressure was 20 lbs lower than normal. I thought the filter waa plugged so I had an oil change done. I let my truck sit off for an hour before pulling in to the shop. When I restarted the truck to pull in the oil pressure read normal... After the oil change everything was normal for 10 minutes,.it is back to reading 20lbs below, at 1300 rpm at 65 mph it is 42 psi. Normal is 62 psi. The engine also wont run over 170 degrees. I had the thermostats replaced recently. What is going on? There have been no warning lights.
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Answered in 9 minutes by:
9/10/2013
Technician: Cat Man, Cat Engine Expert replied 9 years ago
Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 10,344
Experience: I am ASE Master Truck Certified.
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Hi. Thanks for asking your question! I will try and help you out.

 

42 psi at 1300 is right at the minimum oil pressure at that RPM. The minimum is 40 psi.

 

Since you have already change the oil and it did not help. I would suspect 4 other things may be causing your problem.

 

The first is fuel contamination of the oil. I have seen this before. Sometimes an injector O ring can fail or the seal in the transfer pump can fail and put fuel in the oil If this is the case, you should be able to check your oil and the level be high.

 

Next is the bypass valve is open in the oil cooler/filter housing. When these open, the oil pressure normally drops 20-25 psi. I would consider replacing this first.

 

Next is a weak oil pump. Over time the pump relief valve can become worn and open. When this happens, the oil pressure will drop.

 

Lastly is wear on the rod and main bearings. Over time when they begin to get wear, the oil pressure will drop.

 

If there is no fuel in the oil and the bypass valve does not help, I would have drop the oil pan and remove a few rod and main bearings to see how they look. If they are worn you will be able to tell. If they look good, I would replace the oil pump.

 

Please reply back if you need more help or have more questions, I am happy to assist.

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Customer reply replied 9 years ago
Im now reading 32 psi. Should the warning be on? This came on sudden, so the relief valve makes sense. Previous oil checks have been normal.Never mind it finally came on.
Technician: Cat Man, Cat Engine Expert replied 9 years ago

Thanks for the information Rob.

 

Yeah 32 is below the specs. The low oil pressure warning will not happens til 15 psi.

 

I would try the relief valve first.

 

Let me know if you need more help.

Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 10,344
Experience: I am ASE Master Truck Certified.
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