Human Opiate

on a compression test we got
140 for #1, 115 #2, 125 #3, 130 #4.
Could that lower # be a sign of something going wrong?

Bob S. 1984 Silver

Not likely. Look to the rings, or valves. Are you "using" oil?

Bob S.

Danno

Yeah, the oil-squirt test will help differentiate between worn rings and valves.

Also when the rod-bearings go, there's no warning of any kind. I replaced my rod-bearings several months ago and the compression and oil-pressure all indicated normal. From the condition of the #2 rod-bearing, I would guess I was only several weeks away from spinning it and causing some real damage...

Peckster

Doesn't the oil pressure drop when rod bearings are going? I'm a little nervous about my car, after a couple of long, high speed trips. My oil pressure used to be at 5, both at higher revs and idle.

Recently it seems to have droppd to slightly less than 5 at speed and 3-3.5 at idle. There are three variables: I just had my rod bearings done two months ago, my mechanic put in 10/40 instead of Mobil 1 20/50, and it's warmer. Thoughts? I know my oil pressure is acceptable but I don't like the apparent change.

I can't recall the 10/40 making a difference right way. Am I paranoid?

Skip

[quote]Originally posted by Peckster:
<strong>Recently it seems to have droppd to slightly less than 5 at speed and 3-3.5 at idle. There are three variables: I just had my rod bearings done two months ago, my mechanic put in 10/40 instead of Mobil 1 20/50, and it's warmer. Thoughts? I know my oil pressure is acceptable but I don't like the apparent change.

I can't recall the 10/40 making a difference right way. Am I paranoid?</strong><hr></blockquote>

You're paranoid, but that has no bearing on this subject yuck, yuck

FWIW, When I switched from Modil 1 15/50 to Redline 10/30 I lost almost 3/4 of a bar on both idle and throttle pressures. Lighter weight oil does_that.

Talk it over with your mech to get his thoughts.

Skip

ERAU-944

3.5 is good at idle... my 85.5 gets 4 when hot and going, and like 1.5-2 at hot idle... sounds good to me

bs

[quote]Originally posted by Peckster:
<strong>My oil pressure used to be at 5, both at higher revs and idle.
</strong><hr></blockquote>

5 bar at idle with the engine warm?? it sounds like it's your oil pressure sender that's going bad to me...

Danno

"Doesn't the oil pressure drop when rod bearings are going?"

Only if they were ALL worn and about to fail perhaps. I think worn main-bearings would have more bearing on the oil-pressure gauge than the rod-bearings.

Human Opiate

Ok, thanks everyone, your help was much appreciated.

Dave951M

From the compression readings, #2 just may by developing some issues. Compression reading errors come from rings, valves, and headgaskets. (Not necessarily in that order, and it could be a combination). The oil pressure in the car is affected not only by engine temp, but also by oil type. Mine runs at 5bar both while idling and driving until the engine warms up. Then the idle pressure drops to a steady 3bar, running at 5bar while driving. I use 20W/50 Valvoline racing oil exclusively. Would use synthetics except for a pesky oil leak. My oil pressure sending unit is 4 months old as well. Gist of this is that I don't think you will see a significant drop in oil pressure unless and until the bearing gets really, really bad, like failing in the next minute. Trying to tell from you oil pressure guage is misleading since you drive in all kinds of weather and temps. It might be useful if all readings were done at a reference temp only and the guage a bit more accurate. I think your problem is ring or valve since you didn't mention any milkshake in the oil pan.

Dave