Jump to content
AustrianVespaGuy

Rather low oil pressure on freshly rebuilt engine :(

18 posts / 1641 viewsLast Reply

Recommended Posts

So I have my engine all rebuilt, back in the car, and running, which is good, but I have rather lower than expected oil pressure when warm. Low as in when warm, I'm around 10psi and it comes up about 15psi per 1000 RPM. At 3000 RPM I'm up to about 40psi. I'm pretty sure nothing is truly wrong, because I actually have much better/higher pressure at cold startup. More around 30psi at idle and 60psi at 2000, so everything must be working in there, no leaks etc., but when warm it's obviously lower than I'd like it to be. During the rebuild I did have the crank polished and only installed the standard size bearing shells; could slightly higher journal clearances (don't have the measurements there unfortunately) due to the polishing explain this? Oh and it's a brand new oil pump. Is it OK to drive? Thanks for any thoughts! :

-Carl

Share this post


Link to post
Share on other sites

Boy, I would take the pan off and recheck the oil pressure relief in the pump for starters.

It's easy to have it come apart, and parts fall out.

IF I trusted the gauge.

Every engine that I've had that's been in decent shape's made

30psi at 1200, 60 psi by 2500 hot.

Your numbers would be in the 'ok for an older engine' category, but

I wouldn't like them for something I thought should be 'good'

That's me.

Share this post


Link to post
Share on other sites

1. what weight oil are you using? 10w-30 will give lower readings, so I hope it's 20w-50...

2. Dino oil or synthetic? I noticed that my freshly rebuilt engine showed lower oil pressure with synthetic oil; 30k miles later it's still true--not dangerouslly low but lower than the old engine with 204k miles...

mike

Share this post


Link to post
Share on other sites

I had the same issue years ago after I rebuilt an engine.

The oil pressure valve had not seated correctly. I had to drop the oil pan and disassemble the valve portion to the side of the oil pump. That solved the problem.

Share this post


Link to post
Share on other sites

Well, I did change from 10-30 to 20-50, but really no appreciable difference there. Also, we did drop the oil pan yesterday, took off the pump, and made sure the o-ring sealing the pipe to the pump was OK, and put everything back together; didn't make a difference though. I don't really know much more about how the overpressure relief works though with that new style pump. Is there anything else in that area that could be suspect/checked? Thanks again for the responses!

-Carl

Share this post


Link to post
Share on other sites
Well, I did change from 10-30 to 20-50, but really no appreciable difference there. Also, we did drop the oil pan yesterday, took off the pump, and made sure the o-ring sealing the pipe to the pump was OK, and put everything back together; didn't make a difference though. I don't really know much more about how the overpressure relief works though with that new style pump. Is there anything else in that area that could be suspect/checked? Thanks again for the responses!

-Carl

How about the o-ring for the connection where the pipe bolts to the block? Did you check it?

Share this post


Link to post
Share on other sites
During the rebuild I did have the crank polished and only installed the standard size bearing shells; could slightly higher journal clearances (don't have the measurements there unfortunately) due to the polishing explain this?

If the journals had been polished during previous rebuild(s), then bearing clearance could be out of spec which may impact oil pressure. If your machine shop measured or used plastigage, get the clearance numbers.

You might also check the bolt in the spray bar and proper washers above/below it. Good luck. -KB

Share this post


Link to post
Share on other sites

Boy, 'polishing' that would make the mains/cranks loose enough to

drop oil pressure that much seems... unlikely.

But I too would get the numbers. And if the pan's off,

check it myself. It's easy to do, at that point.

t

Share this post


Link to post
Share on other sites
Boy, 'polishing' that would make the mains/cranks loose enough to drop oil pressure that much seems... unlikely.

I agree, Toby ... however, one ought not underestimate what some overlook and/or the mistakes which can be made.

To OP: plastigage at least one journal, if nothing else turns up. -KB

Share this post


Link to post
Share on other sites

No, I didn't check the upper o-ring, because that would involve getting the timing covers back off again (yuck!) and I know I put a new one in there and I don't see how that could possibly be screwed up; not really anything to go wrong up there is there? Also since I am getting up to 30-60psi at start up, there can't be much of an internal leak right?

-Carl

Share this post


Link to post
Share on other sites

You could. At start up, the viscocity is ferociously high.

But it's pretty darned unlikely.

This is an odd one...

t

Share this post


Link to post
Share on other sites

Ok, one last hope before I have it towed to a shop to get the bearing clearances checked. How do I verify that the rocker shafts are really all in the right way/correct ends plugged/not plugged? Otherwise, I think the only thing left is rod/main bearing clearances. . .

-Carl

Share this post


Link to post
Share on other sites

Oh, cripe, yeah-

you want to see a plug in the front of both shafts when you pull the valve cover.

But that would give you zero oil pressure at the top of the head, most likely.

I'd drive the car to the machinist, then they can see it running, hear it,

verify the pressure with their gauge, etc.

hm.

t

Share this post


Link to post
Share on other sites

Alright, well that gives me one last glimer of hope to check for this evening. Otherwise I'll get it towed to a good BMW shop somewhere around here (little scared to drive it if it is a bearing clearance issue) and have them poke around to see if they can find the problem. What an aggrevation! Thanks for the help though guys, FAQ is still awesome, I really appreciate it!

-Carl

Share this post


Link to post
Share on other sites
Well, I did change from 10-30 to 20-50, but really no appreciable difference there. Also, we did drop the oil pan yesterday, took off the pump, and made sure the o-ring sealing the pipe to the pump was OK, and put everything back together; didn't make a difference though. I don't really know much more about how the overpressure relief works though with that new style pump. Is there anything else in that area that could be suspect/checked? Thanks again for the responses!

-Carl

How about the o-ring for the connection where the pipe bolts to the block? Did you check it?

Bot I had this issue. When I bolted the tube to the block I had the washer in but the tube lpate was not sitting perfectly fluch with the block. So the oil pressure forced the rubber o-ring part way out and I was losing oil pressure. I had the same readings you are having

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.




×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.