High oil pressure ???

Hi so I started my lehman 275 one day and the oil pressure started off normal
Which is 40 psi.
As it warmed up it went to 60 psi!!
I shut er down and changed the oil and filter
No change. Start stop run.... Always goes to 60
So I figured ok it must be the guage don't worry about it
That was about 50 hrs ago
No temp change no diesel in the oil.
I did use a multi grade as straight 40 wasn't available. 15/40
So 50 hrs later she is leaking oil out of the pan gasket. A lot. Still sits happy as Larry on 60 psi all day.
I just assumed it was the guage but maybe not so.
Any suggestions?
Surely the change in oil would not make enough difference to get through the gasket, and I am looking at an over pressure situation right?

I can't see any way high oil pressure could cause a leak from the pan gasket. I think that is a coincidence. Replace the oil sending unit and see if that fixes the problem. They are cheap and available from AD or Bomac.

You might check that your crankcase vent is not clogged. This could facilitate pressure build up in the crankcase and exacerbate a leak due to a failed pan gasket. It would not however have anything to do with the 60 psi oil pressure. I would guess that is either the sending unit or gauge.

Do as suggested and check that the crankcase ventilation is working.



Lehman -- check the oil level. If it has risen from where you filled it last time you are leaking diesel into the pan. Called "making oil" but in reality leaking fuel.

Two common sources are:
--the diaphram lift pump can get a pinhole sending fuel into the pan.
--the injector fuel return pipe which is under the valve cover can split/break or one of the nuts at the connection point can be loose. This will feed fuel into the oil.

Do not ignore it. The oil is being thinned and it could cause other more serious trouble.


As far as the goofy oil pressure the best way to confirm/deny is to get a pressure guage, a decent quality mechanical unit of ~ 100PSI range , glycol filled for not a lot of money and plumb it in with a tee where the electric guage connects. It doesn't need to be left there but it will tell you if the high oil pressure is real or if it is guage/sender problem. I used to pay $50-70 for these but the last two were about $20 and they seem to be good units. I was pleasantly surprised.

Do not ignore this either. Goofy pressure readings could be a warning of impending trouble. It may turn out to be nothing but if ignored and it is something the damage could be expensive.

The "old single weight oil" was probably what the engine was used to.

By using a more modern mullti-weight , your engine probably now has modern detergents eating at all the crud.

A leaking pan and other gaskets is normal when this change is made.

If its NOT the gauge the spring and ball in the oil pump pressure regulator will need to be cleaned..

Maybe the new oil will do it for you?

Old oil was rated CD (Compression ignition ) D grade additive package.

The new oil will be CF , the F being higher detergent

FF said:

The "old single weight oil" was probably what the engine was used to.

By using a more modern mullti-weight , your engine probably now has modern detergents eating at all the crud.

A leaking pan and other gaskets is normal when this change is made.

If its NOT the gauge the spring and ball in the oil pump pressure regulator will need to be cleaned..

Maybe the new oil will do it for you?

Old oil was rated CD (Compression ignition ) D grade additive package.

The new oil will be CF , the F being higher detergent

Click to expand...

Don't send this guy down the wrong path.

Commercially available single vis oils have detergents just like multivis.

A stuck regulator will not control oil pressure at a constant 60psi. A stuck regulator will cause oil pressure to either go super high or super low. His symptom is a step change in indicated pressure, but it is still controlling well at the new higher pressure.

This is a symptom of classic gauge trouble. The next step is to put a mechanical test gauge on and read true pressure.

Could be 60psi was/is normal and previously the electric gauge read low, who knows, but nothing wrong with 60psi.

As far as I know, but could be wrong, the pressurized oil on the 275 is not ducted anywhere near the oil pan rail, so his leak is likely unrelated.

Snug up pan rail bolts. As gaskets age, they shrink and bolts get loose. Don't overtighten, just snug.

Check blowby vent for restriction. A good way to do this is to run engine with oil cap off and block fill hole off by hand and feel for pressure building up, there should be none.

First check the pressure with a mechanical gauge, then tighten the pan bolts. And if your oil pressure really is 60 psi, don't worry about it.

I'm not familiar with the Lehman characteristics and don't know the optimal oil pressure. However, in my 20+ years of over the road truck experience, I know that different manufacturers use different systems. Cat uses low volume/high pressure so that optimal is 40-60 psi. Cummins uses high volume/low pressure so typical oil psi runs between 15-20. So, my thoughts are use the mechanical gauge to get accurate pressure, then contact a Lehman guru and find out it's optimal pressure. Then, go from there. And I agree, oil pan leak is probably unrelated and is caused by loosening of the pan due to gasket shrinkage as previously posted.

I'll bet dollars to doughnuts the leak is not the oil pan but the lift pump gasket.

15 wt oil is thinner and takes time for the oil thickener to change it to 40 wt with heat..

That alone could be the cause of the oil pan leaking now.

most likely culprit is a dirty connection, next is a failing sender. Both simple fixes