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?

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?

i would fix all the oil leaks then see how to engine reacts. hard to trouble shoot oil pressure with a oil leak.

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.

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.

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?

in case anyone is wondering, the o-ring is part 14-110J in this diagram
https://www.miataturbo.net/attachmen...ine=1351026532

part number FE1H-14-122B

My kit did not include a gasket or an o-ring for this.

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.

This isn't a VVT motor is it?

It is not. 97 block & head.

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..

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.

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...

I picked up a mechanical oil pressure gauge from Harbor Freight for like $30. It worked fine for checking oil pressure in my car.

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.

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...

Next thought: What about your grounds? If they're bad, or the OP wire is flakey that would do the same thing.

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.

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: https://www.miataturbo.net/attachmen...ine=1351652210

just for fun ...what weight oil? where is the sender located?

It's 10W-40. It is T'ed off of the stock port near the oil filter. The oil feed for the turbo is also T'ed off here. The oil temperature transducer plugs the end of the 2nd T fitting. The turbo has a restrictor installed. See my awesome artwork for reference.

https://www.miataturbo.net/attachmen...1&d=1351654650

I suspect if the oil pressure is near 0 psi (real not gauge error) for any length of time the damage may already be done. More run time = more damage. :-(

I've been there too. One one build, Dirt in the crank oil passage way trashed a rod bearing. Engine went from 80 psi to 10 psi in the first 10 min after startup. Oil pan was full of chips. Fix included sending the crank out for a polish, new bearings, a real good clean, etc. Good luck...

Remove oil cooler sandwich adapter from the equation. I just figured out this morning that my cooler and all of that hose puts too much drag on the oil when cold (it got down to a frigid 60 degrees last night). The relief and bypass open up leaving me with 12psi @2200rpm during warmup. Once it starts to warm up one of them suddenly closes and it jumps up to 38psi and then as it gets completely hot it settles around 22psi at low idle. I think larger diameter cooler lines would reduce the drag a bit. I've probably got 8-10 feet of hose that the little pump wasn't designed for.

Try it without the sandwich and see if it acts normally.

And just having done some research on oil filter manufacturer's sites there seems to be some variation between manufacturers regarding the bypass valve pressure settings. Wix had 8-11psi and one of the others (can't remember who) had 14-18psi. Most have been unlisted.

Re oil filter valve... There are 2.

The "bypass" is intended to permit oil to continue flow even if the oil filter element is totally blocked. (think of someone that never changes the oil in 40,000 miles. Lots of dirt prevents the filter element from flowing oil...) for most of us, this never happens.

The "anti back flow" valve is intended to prevent the oil filter oil from slowly draining through the engine (e.g. Past the Oil pump clearances) when it's not running. This could take hours to empty the filter can of oil. Once the filter is empty, the oil pump on cranking and startup will take longer to reprime the system with oil. This delays time to reach oil pressure (dry start) and is a high wear condition.

The Bypass valve is typically at the end of the perforated tube that runs down the center of the filter.
The Anti drain back valve is a rubber disk immediately under the circle of holes around the perimeter of the mounting face.

Also as noted earlier, trying to push oil backwards past the anti drain back valve will likely have a very high pressure drop. Measuring oil pressure down stream of the filter (in the standard gauge port) will be lower than on the pump side.

Filter and oil system are completely stock except for the T off of the pressure port, obviously. The remote adapter was the first thing I removed when I noticed the problem.

This is basically how it stands now...hot idle hovers around 0 on the mechanical gauge and pressure will not exceed 37ish psi when hot. It basically gets there somewhere between 4000 and 4500 rpm and just stays there.

Some oil filter pix. (none of the filters I use are listed)
Indicates oil filter construction.

http://www.ford-trucks.com/ford-manu...Comparison.pdf

Zero isn't good. Is it possible that the relief valve on the oil pump is hung partially open?

I won't know that unless I tear apart the engine again. I think I'm at the point where it needs to come out, though. Not much left I can think to try with the engine still in the car.

The Oil Pump pressure release valve has unfiltered oil (The oil filter is downstream). If there is something large passing throught the pump, dirt or filings -the valve could be jammed open... is this enough to loose all pressure? unknown to me...


Pre engine removal inspections:

Pull cam cover, see if there is any oil reaching the head,
Check surface of lifters, cam lobes for wear,
Pull one or more cam bearing caps see what the cam bearings look like... The cam has 1/2 the speed of the Crank and typically has less wear.
Remove oil filter, open the can and look for filings and bearing chips,
drain the oil through a kitchen strainer to collect filings,

That is a very good possibility. Been there, done that, and the reason I've removed the factory pressure relief valve and am using an external one.

Didja put the oil squirters back in?