Skitch

Could someone be so kind as to explain how a bad rod bearing would cause low oil pressure? I guess I just don't get that cause and effect. Also, when replacing is there anyway to know if you need standard or oversize bearings before you have everything apart?

Thanks for any info!

Eli Gunn

I just went through this bull**** with my car. Tell me what happened.You have to plastiguage to find out what bearings you need I think.

Skitch

I am working on an issue that started a few weeks ago:

Before the problem:
Cold Idle = 4-5 bar
Warm above 2k rpm = 3 bar
Warm Idle = 2 bar

Now:
Cold Idle = 3-4 bar
Warm above 2k rpm = 2 bar
Warm Idle = less than 1 bar (oil light on steady)

It didn't flip a switch and happen this way it gradually got lower until I stopped driving it. I have checked the OPRV and polished it and checked the torque on the crankshaft pulley as well. I am thinking now oil cooler seals or rod bearing.

F18Rep

Well, I think it is a bit of a reach but theoretically.... the rod bearings have a clearance into which oil is pumped. If that clearance becomes too large, it requires more oil to fill it. That is essentially a pressure drain on the oil pumping system and I suppose (in extreme situations) could be seen as low oil pressure. Platigage is (as mentioned above) a good way to determine the clearance. If oversize bearings are needed, then the crank will have to be machined. I think there are other (more likely) reasons for low oil pressure though.

Here is a look at some bearings from a 170K engine. <img src="http://www.arnnworx.com/Bearings1.jpg" alt=" - " />

924RACR

Looks rather decent! I've got oil pressures similar to Skitch, on the racecar; most recently accompanied by oil temps at about 270. I was only getting around 3-4 bar while screaming down the front straight at Beaverun turning about 5000-6000rpm.

I'm going to be pulling the oil pan soon to check out the condition of the bearings, expect to have to replace the rod bearings. I'm hoping to get away without new mains, as I don't wish to have to pull the motor right now.

Dan in Pasadena

How about the oil pump or the cam bearings?

Waterguy

I gained about a half bar oil pressure at warm idle when I did my rod bearings at 103k miles. The old rod bearings were showing some wear (#2) and #4 had a gouge 1/4 way around starting at the oil passage (metal debris during construction?) I didn't plastigauge the old bearings, but the new standard-size ones were well within spec. The original bearings had a manufacturing date of 1987 and were marked "standard." The oil pan had been off before, though (plastic baffle removed.)

slevy951

Could be a bearing. Have you check the torque on your crank bolt lately? It could be a bit loose which would cause it to lose pressure.

slevy951

Also, drain the oil and look for metal shavings on the plug. If there is metal there, that will be another indication of a bearing getting ready to go.

Skitch

I changed the oil when I was working on the OPRV and noticed some shavings on the drain plug. Is there any amount of shavings that are OK? Or is this a definite sign of failure?

Mighty Shilling

Also, You'd think that if a rod bearing was allowed to destroy itself, in a situation where the owner drove the car for about 150 miles before he decided that he NEEDED to stop cuz he was getting 1 bar oil pressure at 70 mph in 5th gear...You'd think that a chunk of brass from the bearing was sucked up the oil pickup tube and maybe jammed in the oil pump. I'd assume that would cause a lack of oil pressure.

thomschoon

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Porschephile 924:
<strong>You'd think that a chunk of brass from the bearing was sucked up the oil pickup tube and maybe jammed in the oil pump. I'd assume that would cause a lack of oil pressure.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Actually there is no brass in the bearings.

But back to the topic, have you put a secondary oil pressure gauge on to double check your oil pressure? Just buy a cheap mechanical gauge and run the tubing up and through an open window so you start and drive the car and see if you are actually losing pressure. Just saw a $20 sending unit go bad and the guy was thinking he had other problems. Good luck

Skitch

I am going to be able to borrow a mech gauge this weekend to test. Thanks for the help! But..just as a general concept what would make a bad rod bearing cause the low oil pressure? (not that this is what is happening, I just don't get how it could effect the oil pressure) Basically just a general dumb question....

Dave in Chicago

The metal shavings sign of death is a little Christmas-tree-shaped formation of thin metal shavings standing proudly on you oil drain plug magnet. This was the sign to me of bearings getting ready to go.

We changed them. Sure enough, #2 was scored. Crank was fine. I noticed no real difference in oil pressure between the before and after.

Mighty Shilling

How bout this one...I drove 150 miles on a bad bearing (i know...stupid, but I had class in 13 hours and I was 500 miles from campus, and no money for a greyhound.) when I took off the drain plug, and looked at the magnet, it had a little einstein afro on it. it was kinda amusing. I had bearing peices about 1/4 inch wide on the oil pickup. it was disturbing.