oil pressure problems


Well-Known Member
Thread starter #1
my c15 oil pressure usually runs around 60 ,maybe a tad bit more
lately it runs steady on 60 for about 3-4 weeks (about 7000-10,000 miles) and then slowly starts to fall to about 30-35
I change the oil and filter or just the filter and it jumps back up to 60 for another 3-4 weeks
I am going to change the oil and filtet again this weekend and I am thinking of running something thru with
the old oil to help clean the inside then changing the oil and filter.
my mechanic buddy says pour in 1 gal of diesel fuel and let it idle for about a hour
then drain it all out and add new

any thoughts on this or something else to add to it?


curmudgeon extraordinare
If it were my engine,...

I'd have gotten an oil sample sent in and then cut open an oil filter. Cutting open an oil filter is often faster and more telling than an oil sample.

Make sure you notate on the label you send with the sample it's due to falling oil pressure. It's a critical piece of information for the lab. Tells them there's a failure in the engine and they'll possibly be prepared to due additional testing.

The lab results are compiled over time so ever.

Trying to upload one of my reports
Thread starter #41
I cut open 2 filters with a pair of air shears

nothing but filter,no flakes of any kind

thinking of possibilities
no smoke so i guess rings may be ok,but now how about the turbos?my next investigation
rings,air compressor, and turbos
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curmudgeon extraordinare
The program I use is the cat SOS fluid analysis. Easy peasy and they have a record.

Go to your local cat parts counter and ask for the sample kits.

Cat | S•O•S Services | Caterpillar

Loss of oil pressure is generally an indicator of bearings failing and getting excessive wear. So analysis is critical as well as not operating the engine till you figure it out.

It's only $20,000+ to rebuild it after all and $40,000to replace.


Professional Pot-Stirrer
I am planning on it

I usualy get the oil computer anazlized, about once or twice a year but never used CAT
The benchtop analysis really isn't accurate for a number of reasons. If you're going to spend money on it, a full service lab that uses serious analytic equipment operated by trained technicians is the way to go. I pull a sample every 25,000 miles.



curmudgeon extraordinare
Cam bearing and crank bearings are the biggest culprit for loss of oil pressure.

Otherwise it would be your oil pump itself.

The symptoms you describe...

Now that you've gotten a clean oil sample. Your oil filters are clear.

I'd have a shop drop the oil pump and measure it for specifications. Have the oil pressure relief valve tested too.

I'd also consider having a mechanical gauge temporarily installed to verify the ecm reading is correct. I'd probably start here first before opening the engine up.

If the mechanical gauge and dash are different, I'd replace the sending unit


Well-Known Member
its been a while but when I used Blackstone they would compare my sample to the average of other engines of my spec (3406b) and mileage. Maybe call and ask if they still do.
Oil samples are the most useful when done in secession as the engine wears but I think it’s worth it for you to have one done.


Well-Known Member
Thread starter #11
I`ll check with them.I called them about a month ago and discussed a inframe,he said a ballpark figure was 30,000
including the twin turbos and a 4 year unlimited warranty.
A buddy got his done there,it ended up about 27000.He has the same cat motor I have and he got his hp cut up to 550 hp and 99 mph top end included


Well-Known Member
I just went to Cat and got 3 kits
planning on sending one in today
I was told by a cat guy to do more than one to see a developing pattern.
You can buy a kit that will allow you to draw some oil out of the crankcase using the dipstick tube if you want to do a shorter interval than your scheduled oil change. I bought one from Blackstone long ago. Maybe CAT has one available as well.