Low Oil Pressure

[Deucenut]

Hi all,

The oil pressure gauge on my new to me M35A2 is showing 30 PSI when cold and nill when hot at about any RPM. I have checked the oil level, am trying to get the sending unit out so I can check it, and have removed the oil pressure regulator and all looks good there. That is where the TM help seems to stop.

The truck came from GL and I am still working through the bugs with it so I do not have a history of the truck. I know it was overhauled in 89 though.

Is there something else I should be checking or am I in for a bearing job? Any help?

Thanks!

 

[renovate7]

Screw in a manual gage where the sending unit was. This should tell you what you really have for pressure.

 

[doghead]

Is your oil diluted with fuel? Is your FDC still connected?

 

[Deucenut]

I will try a manual gauge but the way it is acting I do not believe it is a gauge issue. The oil is not diluted and the FDC is bypassed. I have no doubt that this is a presure issue caused by some problem within the engine. I recall reading about an issue with the pressure relief valve on the oil pump but have not been able to find the thread again.

Any more ideas?

 

[doghead]

Confirm the pressure next.

 

[uscgmatt]

Make sure your sender and gauge are the same pressure range. Mine had a 0-60 sender with a 0-120 gauge. Scared me until I found out.

 

[m35a2cowner]

If its new to you, make sure the oil filters are in correctly. If your wondering about the internal parts of the engine (fuel dilute too) send a sample of the oil off for analysis. Its relatively cheap and you will get a good idea of the condition of the motor. When testing (or operating) a mechanical oil pressure guage (not a cheapo) is best.

 

[crazywelder72]

Screw in a manual gauge where the sending unit was. This should tell you what you really have for pressure.

toss out the original gauge and sender and get a mechanical gauge. There about $30 i think. I got mine from summit racing.

There are too many variables with what is there now so by replacing it with a mechanical you will know for sure what the psi is. I would do that before i started looking at oil pumps or sending fuel out for analysis.

 

[Deucenut]

Here is the latest update. I pulled the oil pressure sending unit and it is for a 120 psi gauge by both part number and resistance readings. I have a 60 psi gauge so that is one problem solved. I have ordered the correct sending unit and will install it and see what it reads.

I should have included in my original post that I changed the oil and filters as soon as I got the truck. The oil is not diluted but, per m35a2cowner's suggestion, I will send a sample of the oil off for analysis when I next change it.

Thanks all. I'll keep you posted.

 

[uscgmatt]

Glad to help, at least its a cheap fix.

 

[cidrich]

Deucenut, My deuce had a 120 psi sender and a 60 psi gauge in it when I got it from Fort Jackson, SC. When hot it had between 5 and 10 psi at idle and 25 to 30 psi going down the road. It scared me like it did you until I figured it out. Put a 60 psi sender in it and I now have 40 psi hot at idle and 60 psi going down the road. I would hook a manual gauge to it and see what you have. I hope it turns out for you like it did for me!

 

[Deucenut]

Final report. I installed the 60 PSI sending unit today (thanks Erik) and went for a drive. 55 PSI at cruise and 20 PSI at idle, both hot readings. I am a happy, and relieved, camper.

Thanks all.

 

[doghead]

That's great news!