Replacing oil pump

T

TheTallOne

Daily Driver
I just got a new oil pump from Midwest Bayless for my '81 X, and as instructed I swapped the foot of the old pump onto the new one.

Trying to use all "new" parts that I could, I put the spring from the new pump in, but was forced to use the old bypass pin that the spring pushes against as the new pin was slightly to large a diameter to fit the hole in the original foot.

The new spring was noticably heavier than the original, which I assumed was a good thing since we've always had fairly low pressure at idle ~30 psi, and even at full throttle ~45 psi (at the low pressure light port as read by an analog electronic autometer gauge)

Now my oil pressure has has jumped to 80 psi at 1500 rpm and I'm afraid to give it gas for popping seals, because I don't know then the relief valve will open.

This is a lemons racecar, so I have time to get fixed, (though I'm hoping to do the fix without taking the engine out again) I'm just trying to get oil pressure reading right.

Has anyone else experienced this, have recommended pressures at the low pressure light port, and have suggested fixes? Thanks!
 
My Miata has very high cold oil pressure so until it warms up I baby it. Once warm it settles down.

Carl’s question is very pertinent to the problem you face.
 
Usually low pressure is more a result of worn engine internals than a worn pump. Also the relief valve typically does not affect idle or low RPM pressures, only maximum pressure at higher revs. I'd double check that the combination of parts you used for the relief valve are correct. It may be starving the engine of oil flow.
 
80psi @1500rpm doesn't sound too unreasonable for cold oil. My daily tends to be ~90ish on a cold start, down to around 20 at 115c (operating temperature).


Were your previous measurements at a higher engine oil temperature? Oil takes FOREVER to come up to temp, especially on cool running older engines with a relatively large oil capacity for their displacement, like ours.
 
Jonohhh said:
80psi @1500rpm doesn't sound too unreasonable for cold oil. My daily tends to be ~90ish on a cold start, down to around 20 at 115c (operating temperature).


Were your previous measurements at a higher engine oil temperature? Oil takes FOREVER to come up to temp, especially on cool running older engines with a relatively large oil capacity for their displacement, like ours.
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That's excellent news. I'm going to try letting it warm up fully later this week and will report back. Currently waiting on an HEI heatsink

The old measurements were a bit higher cold and the rest of the time at 40 psi was sustained high rpm during lemons races. Rarely below 5k rpm
 
TheTallOne said:
That's excellent news. I'm going to try letting it warm up fully later this week and will report back. Currently waiting on an HEI heatsink

The old measurements were a bit higher cold and the rest of the time at 40 psi was sustained high rpm during lemons races. Rarely below 5k rpm
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EDIT: just to confirm, you mean 60°F Ambient temperature?


If you don't have one, I'd definitely invest in an oil temperature gauge. By far, it is one of the most important engine status indicators. Coolant temperature doesn't really matter unless it's overheating, but oil being up to temp before high load and revs is extremely important for engine longevity. In track applications where there's extended periods of time at high revs and load, being sure the oil doesn't get too hot is also important, though I'd be surprised if a motor making 50hp/L is really gonna push oil the oil past the safe zone.

I don't have any direct experience with motorsport on this platform, so I can't say whether or not oil temperatures are an issue, but I just wanted to mention it because it is important.
 
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Jonohhh said:
80psi @1500rpm doesn't sound too unreasonable for cold oil. My daily tends to be ~90ish on a cold start, down to around 20 at 115c (operating temperature).
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115 C? Like 239 F? Wow! Are you sure that's correct? Seems like about 50 degrees too hot! What am I missing?
 
79X1 said:
115 C? Like 239 F? Wow! Are you sure that's correct? Seems like about 50 degrees too hot! What am I missing?
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OIl needs to get above 212 to boil off the water and other condensates. 115C is about right for normal oil temp when the car is fully up to temperature. My Scirocco had an oil temp gauge (and not many others go figure) so I became quite aware of oil temps.

VW has a oil to coolant transfer cooler which assists with keeping the oil temperature in a reasonable range.

VW flat fours were an air and oil cooled engine…
 
79X1 said:
115 C? Like 239 F? Wow! Are you sure that's correct? Seems like about 50 degrees too hot! What am I missing?
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Yep, that's on my daily driver though, not my X1/9. Unfortunately I've yet to install additional instrumentation on the X.

The car in question is a mid 2000s bmw with a mapped cooling system (ECU controlled thermostat and water pump), so during cruise it increases coolant temperature target to around 220f for efficiency, and down to 175 during hard driving. Oil temperatures follow, ranging from 205 to 265f. Hot, but within reason, and doesn't pose a risk of engine damage or excessively quick oil degradation with modern synthetics.


During our Formula SAE competition we got up to 142c in our Yamaha R6. Admittedly I was quite uncomfy.
 
Not fully up to temp, but here's the behavior now. Oil pressure shoots up with rpm. I didn't want to keep idling once it got dark as it's rather loud, and I'm not street legal right now so a drive isn't in the cards
 
General rule of thumb for most engines is 10psi for every 1000 rpm. I would expect the relief valve to open before 100 psi.

80 psi at idle is too high. I would let it warm up and see what it does at normal operating temp. If you don't have one already, go to Harbor Freight and buy an infrared temp gun and monitor the temperature of the oil filter. Figure it should be 180+ once fully warmed up. And then check the pressure gauge. Also, you might try an external gauge as I have seen the cheapo dash gauges be off by alot.

For most of my cars I simply made up a shim to go under the relief valve spring to give it some preload. That helped bump the base pressure a little and raised the vent pressure up to the desired 80-90 psi.

My DSP autocross car always ran 5W30 Mobil 1 Synthetic.
 
Steve Hoelscher said:
For most of my cars
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Hey Steve (slightly off topic) from memory the factory did not use a gasket between the pump and engine block. Is that correct? I have a gasket in a set, do you normally run with or without a gasket?

It's been 20 years since I've been in an engine, so I can't really remember... :)

I ran a PBS high pressure oil spring in my race car (just a different spring rate that they figured out would work).
 
myronx19 said:
Hey Steve (slightly off topic) from memory the factory did not use a gasket between the pump and engine block. Is that correct? I have a gasket in a set, do you normally run with or without a gasket?

It's been 20 years since I've been in an engine, so I can't really remember... :)

I ran a PBS high pressure oil spring in my race car (just a different spring rate that they figured out would work).
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Yes, there is a gasket between the pump and the block. If there wasn't you would have a pressure leak there. It should come in the kit.

And just in case, I would NEVER use RTV there.
 
TheTallOne said:
The pump comes with the foot for the 128 or 124 (can't remember which) but either way it is shorter and at a different angle than the one used in the X to reach down into the sump
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Probably a 128 pump. Its a shallower pan and the motor is canted forward more so the pickup is angled more.
 
Does anyone have tips for removing the pan without taking the engine out of the car? I'd like to not have to drop the trans out completely
 
TheTallOne said:
Does anyone have tips for removing the pan without taking the engine out of the car? I'd like to not have to drop the trans out completely
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Put a jack or stand under the gearbox as close to the engine as possible. Then remove the cross member bar and you will have access to all bolts on the oil pan
 
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