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Old 10-20-2012, 09:33 PM   #1
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Default New engine, oil pressure drops above 4k RPM -- Hit me with ideas

Just went for a first drive. Built the motor myself over the summer. Oil pressure builds like expected until 4k RPM or so and then drops down to 25psi or so. Hot idle I'm seeing 10-12ish.

Motor has BE gears and I have a VEI gauge/sender installed. Letting it cool down now. Also have some oil leaking at the front of the crank. About to go start taking things apart and troubleshooting. Anyone have some ideas as to what would be causing the pressure drop?
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Old 10-21-2012, 12:33 AM   #2
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Update: I have three spots that are leaking -- two remote oil filter hose fittings and probably the front crank seal (somehow). Got the crank pulley off and calling it quits for the night. Since I was getting normal oil pressure until 4k RPM I was hoping maybe there was a leak at the pressure transducer or the fitting its tee'd off of on the side of the block. However, everything in that area seems to be OK.

I can't see the leaks at the remote oil filter housing being anywhere close to big enough to cause any sort of appreciable pressure drop. When I saw the pressure drop the first time I let off the gas, I pulled over and made sure I was still getting safe pressure. I took off again and had the same thing happened. The oil pressure seemed a little jumpier than expected on the mile or so back to the house (would jump 3-4 psi at times).

Any advice on how I should go about troubleshooting this? Relief valve issues? Something else I'm missing?

Last edited by messiahx; 10-21-2012 at 11:13 PM.
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Old 10-21-2012, 10:22 AM   #3
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i would fix all the oil leaks then see how to engine reacts. hard to trouble shoot oil pressure with a oil leak.
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Old 10-23-2012, 01:40 PM   #4
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Seens something similar before. Did you forget the o-ring between the pump and block? Granted what we saw was great OP until about 4K and then it would just hover around 40-psi(we assumed while it was spraying out of the block/pump interface)
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Old 10-23-2012, 05:44 PM   #5
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Quote:
Originally Posted by tpwalsh View Post
Seens something similar before. Did you forget the o-ring between the pump and block? Granted what we saw was great OP until about 4K and then it would just hover around 40-psi(we assumed while it was spraying out of the block/pump interface)
Good question. I think I did overlook that o-ring....damn.

Last edited by messiahx; 10-23-2012 at 06:32 PM.
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Old 10-23-2012, 05:51 PM   #6
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Quote:
Originally Posted by tpwalsh View Post
Seens something similar before. Did you forget the o-ring between the pump and block? Granted what we saw was great OP until about 4K and then it would just hover around 40-psi(we assumed while it was spraying out of the block/pump interface)
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Good question. I don't remember. I sure hope I put that in. If not, the engine has to come out I'll have more time to troubleshoot it later in the week.
My engine gasket kit from ebay did not come with one of those. My machinist sourced the o-ring from the local gasket shop. So depending on where you got your gasket kit from, it may or may not have had one. I could see if the motor was already apart forgetting that o-ring removed that you could forget it on rebuild.
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Old 10-23-2012, 06:08 PM   #7
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Does it rise up then drop suddenly and stay steady at that lower pressure? Like the oil filter bypass popped open after it got so high?
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Old 10-23-2012, 06:08 PM   #8
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in case anyone is wondering, the o-ring is part 14-110J in this diagram


part number FE1H-14-122B
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Old 10-24-2012, 12:21 AM   #9
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Quote:
Originally Posted by shuiend View Post
My engine gasket kit from ebay did not come with one of those. My machinist sourced the o-ring from the local gasket shop. So depending on where you got your gasket kit from, it may or may not have had one. I could see if the motor was already apart forgetting that o-ring removed that you could forget it on rebuild.
My kit did not include a gasket or an o-ring for this.

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Does it rise up then drop suddenly and stay steady at that lower pressure? Like the oil filter bypass popped open after it got so high?
Yes, this behavior is exhibited, though I'm fairly certain it's this missing o-ring. I remember thinking that it was odd that I didn't have a gasket, did some googling and read somewhere that there was no o-ring, so I just RTV'd the sucker and put it on.

Turns out there are two different "styles" of pumps for our motors. Some have a recess for an o-ring, and some have a flat machined surface that requires a paper gasket. Mine needs an o-ring. I treated it like a flat faced one.

Also, I purchased from the first batch of the BE street pumps, which did not include the o-rings. Start at post #86. https://www.miataturbo.net/group-buy...y-63294/page2/

I'm 99% sure my problem (mistake) is not having that o-ring. The motor was a complete tear down and rebuild. I tossed the old pump without thinking about it. Totally my oversight, though some quick Googling gives me a little consolation in that I'm not the first to make this mistake.
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Old 10-24-2012, 11:50 AM   #10
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This isn't a VVT motor is it?
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Old 10-24-2012, 05:46 PM   #11
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It is not. 97 block & head.
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Old 10-24-2012, 07:33 PM   #12
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im just getting my car back together, I bought one of travis first pump as well. It did not come with a oring. I dropped off all my parts to a local engine builder back in May. I hope he put the oring in! this post makes me nervous! i may pull my motor and pull my pump to verfiy..
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Old 10-30-2012, 01:18 AM   #13
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Update: Pulled the oil pump off, confirmed that the o-ring was missing and installed it. Discovered another issue while I was working on it -- the hollow stud the oil filter threads onto was backed all the way in, a definite restriction. Not entirely sure how that happened. Maybe it broke loose and twisted in when I installed the filter relocation adapter.

The oil pressure is still inconsistent. There is a 10-20 psi random deviation, depending on RPM. At a hot idle the gauge bounces anywhere from 2 to 12 psi. I'm going to grab a cheapo 0-100 mechanical pressure gauge tomorrow and install it to double check the VEI gauge.

I'm not expecting the new gauge to read any different. If I get the same jumpy pressure on the mechanical gauge, where should I go from there? I'm really stumped on this.
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Old 10-30-2012, 02:12 AM   #14
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Bad news check... When you pulled the oil pump, did you have any metal chips or filings in the pan? You could also open the filter to see if there are any chips there. Too low oil pressure is hard on everything. Main bearing or rod bearing failure can be seen as larger chips (1/8 inch across or possibly larger and often paper thin).


Erratic oil pressure could also be from air in your cooler and lines. This should be ok after the first startup... But, an oil cooler that can drain back through the engine when not running requires priming each cold start. Not good. Mounting the cooler with the hoses at the top helps...
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Old 10-30-2012, 11:07 AM   #15
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I picked up a mechanical oil pressure gauge from Harbor Freight for like $30. It worked fine for checking oil pressure in my car.
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Old 10-30-2012, 11:14 AM   #16
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There were 3 or 4 small chips and some RTV stuck to the pickup tube when I pulled everything apart. Didn't see anything floating around in the pan or the oil I drained otherwise.

I don't have a cooler and the relocation kit has been removed, filter is in stock location.
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Old 10-30-2012, 01:07 PM   #17
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Another thought, An oil filter (normally) flows from the outside through the paper to the centre then, out the threaded tube back into the engine. On the back side of the circle of holes (oil filter inlet) there is a rubber disk that acts as a one way anti drain back valve On must filters (to keep the filter oil from draining back into the feed side).
If the filter was on a remote mount and connected in reverse flow (hoses reversed) then the pump would be pushing against the filter's anti drain back valve. I don't know what the pressure loss through the filter would be in this case... May be significant.

No other ideas...
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Old 10-30-2012, 10:47 PM   #18
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Next thought: What about your grounds? If they're bad, or the OP wire is flakey that would do the same thing.
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Old 10-30-2012, 11:45 PM   #19
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just to add, I've had several issues with senders and grounding fr oil pressure. not sure what you have but Ive used vdo, and Ive had a few issues. dnt think a bad sender or ground would account for what you describe but who knows.

Last edited by psreynol; 10-30-2012 at 11:55 PM.
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Old 10-30-2012, 11:56 PM   #20
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I removed the electrical sender and installed a $20 O'reilly mechanical gauge in its place. When I first started the car, it read 50ish and at a completely warmed up idle it would hover around 0. As soon as I touch the gas pressure goes up, so I took it for a spin. Pressure would never break the mark between 25 and 50psi, so figure 37ish. This behavior was consistent.

I did not see any of the jumpiness I did on the VEI gauge, though I suspect this can be attributed to the slower response of the mechanical gauge. Also, where pressure would peak and then drop to 25psi before on the electrical gauge, I only see it rise to that 37psi mark, which it hits somewhere between 4000 and 5000 rpm and just stays there until I let off and coast down. I brought it to 6000 rpm a couple times and held to confirm the behavior.

At my day job I'm a calibrator so I may bring the gauge in and check it's accuracy just for kicks, but clearly my motor is experiencing a pressure issue. If I pull the motor at this point, I'm not even sure what to look for other than rechecking all the clearances and the bearings for wear.



Bought this gauge:
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