One extreme to the next

[Drillman]

I've been dealing with apparent high oil pressure and fitted a mechanical gauge to confirm.
NO HIGH OIL PRESSURE original gauge telling lies
Mech gauge shows 45 psi idle cold and 55 psi driving
Warmed up and 2000 rpm running 45 psi but idle at about 4 - 5 psi
Any light touch on the throttle and pressure comes back instantly
When driving and I back off the gas the gauge steadily comes back until about 18 psi when it falls like you've shot it to 0 then comes back to 4 psi.

Any ideas what I'm likely dealing with this time?
Filter bypass valve?
Oil cooler blockage?

Truck done 370,000 kms
Runs beautifully, no nasty noises, no oil usage, oil clean, burns clean and good fuel consumption rates

[Robyn]

The later 6.5 engines (96 and up) have oil squirters in the main bearing webs.

These holes in the main line have little aluminum orifices in them to shoot a stream of oil at the bottom side of the piston crowns.

After the oil temperature comes up the pressure drops off a lot at idle due to the 8 LEAKS in the oil system.

I have never seen one drop off to zero and then creep back up.

4-5 psi is a bit low even for a squirt block.
The last squirt engine I built up would hold 15 psi at idle hot


Depending on several factors (Miles on the engine and wear) the low pressure might be explained.

One worry on these squirt blocks is MAIN WEB CRACKING

I have seen center main webs (3) crack through the oil squirt holes and then the crack propagates up into the lower cylinder area.

This sort of anomaly could explain the low pressure.

The drop to zero makes me nervous.

About the only way to really know whats going on is to pull the engine out and strip it down.

Sadly to get a good look everything needs to come apart including getting the crank out and washing the block so a visual can be had......


If the block shows no main web cracks and BE SURE ALL 8 SQUIRT NOZZLES ARE IN THE SQUIRT HOLES then a fresh set of bearings including the cam bearings and a new oil pump will be the ticket to getting the pressure up to where is needs to be...

The squirt engines use a high volume pump.

A standard (Early engines) pump will not deliver enough oil....


Sorry I can't be more positive.

Good luck
Keep us in the loop

[DmaxMaverick]

That pressure is too low if the gage is accurate.
The bypass/relief valves are possible (and easy to replace), but they would be on the list of least likely. Assembly seal compounds can foul them, but that's about it. Other fouling indicates another failure, and they would be the least of your problems. Doesn't sound like it to me.
The oil pump is possible, but they rarely ever fail or weaken. Most likely, if they are a problem, defective since new.
Perhaps have a look at the oil you're using. What brand and grade? The 6.2/6.5 can be a bit picky, and sometimes it's only that simple. Most 30W will cause complaints of one type or another.

[JohnC]

My first guess would be that the oil pressure relief valve is sticking, or has some crud stuck in it, or both.

[Robyn]

I hate to be hanging crepe....but my worry is a cracked center main web....

[Drillman]

Thanks guys
I'll start with the easy stuff and do the bypass valve and fresh 15w40 oil. I did change to 10w30 when I thought I was dealing with high pressure.
Grasping at straws I know but have to start somewhere.
Do you need any special tool to change bypass valve?

[snarl]

What brand oil filter?

[Drillman]

Used a Ryco filter last change

[Yukon6.2]

Do you still have your old filter?
If you do cut the can open and have a look at the media inside.
If not it may be worth the cost of a filter to cut the one you have on the engine now.
It inside may show signs of the reason for low pressure,ie metal in the filter.

[a5150nut]

Or an oil sample sent in for analysis