weird oil pressure problem

[spoolint78]

Alright guys, got another weird oil pressure issue.
My last low oil pressure issue was resolved by replacing the broken oil pump drive shaft. 1000km later, the oil pressure has been good, but has since started to drop recently within the last few days. Only thing I did was install 720cc injectors. FP is down to 30 with the vacuum on, a/f's are around 14.8 crusing and idling, and 11.50 at wot, so I'm pretty sure I can rule out gas washing down the cylinders and getting into the oil.
At cold start the oil pressure is around 70psi and cruising while its warming up it gets to 35+psi.
However when it gets fully warmed the oil pressure just hovers around 20psi at 3000rpm and no matter how high I rev it, the max I will see is around 30-35psi close to redline. For those who don't know, I have a complete remote oil relocation setup with an rx7 oil cooler, -10 lines, etc.

The weird thing though is when I give it gas, the oil pressure drops at least 5-8psi, and then when I let off it rises by 5-8psi.
Anyone have any suggestions?
Perhaps the oil is breaking down (5w30 castrol oil).

Any input is appreciated.
Thanks

 

[jdub]

Refresh my memory...has the stock filter head been removed?

Was the oil pump shimmed?

 

[spoolint78]

oil filter housing has been removed.
Stock oil pump shimmed.

 

[jdub]

I hate to say this, but it's looking like a oil pump (shaft or pump itself). Oil degrading should not cause that much of a drop...you could change it to make sure, but I doubt it.

You might want to check the RX-7 cooler is not creating a return restriction to the motor. Just bypass it with a double male end -10 splice and see what the pressure does.

 

[spoolint78]

I'll look into changing it.
I googled a search and someone with another car had similar problems and suggested it was the oil pump relief switch in the pump itself.

But if this were the case, wouldn't I have low oil pressure even on start up?

 

[jdub]

It's called the pump relief valve on the 7M...it's what you shimmed. How much did you shim it?

That depends on the spring condition, but you are correct...pressure should be lower than what you are showing. That's why I suspect the pump itself. You could be having another shaft issue too.

Make sure it's not the cooler like I said above...that's easy to check.

 

[spoolint78]

Ok, i will check the cooler first.
Pretty sure the oil pump was shimmed 5mm.

Checked the oil pump shaft pulley, seems ok but didn't get a chance to remove the lower timing cover and physically inspect the shaft in and out play. It did however spin fine though.

Any explanation regarding why the pressure drops 5-8psi when giving gas, and rises when I come off? I found that odd.

jdub, would a possible clogged oil filter cause this?
Something else I could look into real easily.

 

[jdub]

That is odd...does the pressure drop stay constant while you're accelerating, then reach a constant speed with the same gas pedal pressure?

Assuming you're using a quality filter (like a Wix), the filter clogging up would just put it in to bypass. Oil would just flow directly to the outlet.

 

[grimreaper]

well similar issue, just got it running. Cold psi is normal 20+ idle and low 40's crusing. Once hot i cant get it above 20-25 psi. I stopped revving at 3800 rpms. idle is perfect 4-10 psi. No shims on the pump, stock filter head with relief valve blocked shut routed to remote filter head. Small leak on the return line from the cooler. No spray like id expect from a leak causing psi drop, just a wet connector. rx-7 cooler too. can a seamingly small leak cause this much pressure drop?

on acceleration mine will jump to 20-25psi instantly then "wiggle" a bit as rpms increase bit not rise much over 20 psi

dont mean to thread jack just the thought two birds with one stone come to mind...

 

[IJ.]

What sort of gauge are you reading this on Spool?

 

[spoolint78]

defi oil pressure gauge.
I'm using a regular castrol oil filter as well.
And I do have a leak at the Cam position sensor.

 

[jdub]

Castrol filters are made by Wix. The MaxPro uses conventional media, the MaxPro Plus use a synthetic media.
The filter definitely should not be the cause, nor should the leak at the CPS.

One other thing could cause this...the piston squirters. If one or more is stuck open or opening early (more likely) it would be a pressure bleed on the system. What you are seeing suggests it...at idle the squirters are closed (good pressure). If they are opening at 20 psi (vs ~40 psi spec), oil pressure would slow/stop building as RPM increased and the increased pressure from the pump forced the squirters open more.

Another possibility...the bearings. I don't think this is as likely though.

 

[spoolint78]

I am 99% sure this engine does not have oil squirters.
Engine bearings, not sure. I have driven the car on the highway for almost 120km before it clicked in that my oil pressure wasn't rising and no signs of rod knock.
I will keep you guys posted, thanks for all the tips.

 

[grimreaper]

Take the thermopelet out and run it with out it installed. In theory it should run higher oil psi since its bypassing MOST of the cooler like it does when the t stat is open. Since this is the ONLY thing i have changed on mine, it is starting to look like the coolers pressure drop is more then the oem pump can flow.

im taking mine out of the loop i just dont have time until later in the week to pull the lines off. hopefully it is the cooler.

adjuster is the only one i know of that has run this cooler with out a psi drop. Previous post by him state his pump is shimmed at 10mm. Another local guy told me to expect a pressure drop as his lost some too with the rx-7 cooler, i just didnt expect this much.

 

[spoolint78]

Will do, I'm leaning towards that as a possibly culprit. I doubt it could be the filter, if it was an issue I believe I would have low pressure anytime the car is running.
I'm gonna bypass the oil cooler lines completely.
Reason why is If I take out the thermopelet wouldn't the oil cooler still fill up with oil first, then exit the oil cooler? I would think that I would have to close the inlet inside the oil cooler going to the fins and just let the oil flow in the oil cooler endtank at the bottom, and flow right out into the outlet (i.e. not flowing through the actual oil cooler).

 

[Fletch124]

Its got 6 quarts in it right...?

 

[jdub]

Should be more than that with a cooler that size

 

[grimreaper]

cooler holds full qt + filter and lines,

There is ALWAYS flow through the cooler. When the oil is cool enough to keep the thermopelet from expanding and shutting the bypass port a good portion bypasses it just not all of it. Have you noticed from a cold start its like a switch is being flicked from when you have decent oil pressure to a point that it levels off a bit above 20psi (not the gradual decrease from the oil getting to operating temps)? This is how mine acts. No thermopelet, same amount of flow through bypass with a theoretical drop in psi when oil gets warmer, just not as much. I cant get to my IN line with out dropping the cooler other wise id stop speculating and back it up

 

[grimreaper]

Took the thermostat out, oil psi is back to normal. Still some very light bleed off to the cooler but over all psi is back to climbing in the 30+ range above 3000rpms like before the cooler install. Guess the cooler has to much of a drop across it for safe use with a non shimmed (or possibly lightly shimmed) oil pump.

Jdub mentioned the delta P = change in pressure. What plays into affect on a cooler to cause the drop? end tank size and passage ways?

 

[jdub]

Cooler design...the size of the passages, the end tanks, etc. It's the same as you would see on a cheap IC having a big boost pressure drop. Line size to the cooler will have an effect as well...Spool was showing a bit less pressure than you Grim and he is using -10 lines.

I suspected the cooler may be the reason, but I need one of you guys to prove it. Shimming the oil pump a bit more (7-8mm) would help. I think a better solution is to use a more conventional cooler configuration like the B&M.