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Motor General

Oil pressure too high when cold?

We've all seen/done/read about this problem - cold start oil press goes off the gauge (100 psi), only 60 warm.
Thinking about what to do. Bill Jenkins solved this for Chevy 25 years ago - the max press relief port isn't big enough at 5/16", so he removed the plug and re-drilled the passage leading from the relief valve back to the feed side to 3/8".
Concerned with LA pump - is the relief port visible on the casting? How big is it? Anyone have a picture?
Normally the relief port exhausts to the intake, but this isn't really necessary. If accessible, another hole leading to the pump exterior could be drilled to allow more volume to be dumped when the valve is open. The hole could be positioned at the far end of the relief valve travel, so it's only used when the valve is fully open. Excess oil would dump right into the pan. If (for example) the existing port was 3/8" ID, an extra hole 3/16" diameter would add about 23-24% to the volume.
Effect (if sized correctly) that cold press and hot press would be much closer and predictable.
Thoughts? Experiences?
Thanks. ejit

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this is an interesting thought. i've "played" with pr valves over the years in bb, sb, slant6 & 2.2 4's. i have "ballooned", blowed up, blowed off, & split filters, as well as blowed out filter gaskets. sometimes you just don't know when to quit when playing with pr valve. i never gave a thought to enlarging the relief port. would it matter how big to go, as this would be just a dump?[within reason of course].also,in your example, wouldn't 3/16 hole size add 50% in volume as it is 1/2 of 3/8? please expand on this thought if possible. thanx in advance! moparx

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I have done quite a bit of playing with this on the TT340 as I have a very large pump and relatively tight clearances. I like the big pump so that I can hold decent pressure at idle while feeding the turbos, on hot days.

You are looking at a couple of issures at cold startup, when compared to warm. The oil is much thicker and will resist flow through wherever you put it, and the engine is also running at higher than warm idle speed, so you are pumping a much higher volume of oil when compared to warm.

The relief valve in the pump is the big part of controlling the cold startup overpressure situation, as was stated. On the TT340, I did a very careful "port and polish" job on the relief valve passages to decrease the resistance to bypass flow. While it did help, it did not cure the problem.

The next thing that I found was that the valve itself would bottom out in its bore before it would open all the way. I removed the casting flash and burrs that were causing the hangup, but found very little difference in cold pressure spikes. This told me that the valve was never trying to open all the way.

I swiched to a lower pressure spring in the relief valve (I checked both the high and low pressure springs to make sure they would compress far enough for full opening) just to see what would happen. It should have made no difference cold, as the valve would still be all the way open. My cold start spikes got much smaller, and were in the non destruction of filters range of under 100 psi. For this to happen, the lighter spring would have had to allow the relief valve to open further. If the valve had been all the way open on the stiff spring, the same (lower) pressure would have been seen.

I think what happens is that with the stiffer spring, and the high bypass required to hold pressure, you don't get the bypass valve all the way open, as the spring is getting so compressed it is generating too much force on the valve. If you have put a washer behind a standard spring, it would be even worse, as you could take the spring solid before the valve was all the way open.

If you can't stand a softer spring, you could make a "cup" type retainer to replace the press in plug and go with a longer spring, that would give you a more linear spring rate. I don't recall if you have a lot of room to do it however.

If you are having the same problems as I did, making big bypass passages back to the pan would probably not be the cure all, as the restriction is at the valve itself. booster

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I just heard from someone with a Buick, and he ported out the relief passage in his (cover-mounted) pump, and said it made a big difference. Also: the Buick high pressure springs COIL-BIND before the valve is fully open so it's not excess spring pressure but infinite pressure, and in some cases (as you said) the valve cannot move far enough back in its passage to completely expose the exhaust port.
I'll give you another variable: the valve has ports around the OD that connect the rear of the passage to inlet pressure. These ports are only exposed when the valve has opened far enough (idea is to reference output pressure against inlet pressure rather than crankcase pressure). I'll bet they don't line up if the spring is too stiff, and that the "as cast" rference ports may not always be in the right place.
This should be easy to bench test with a parts washer on a gutted pump - just measure how far the valve moves (from the open plug end) before the relief is full, then see if the spring can compress to that length. Buicks eat their cam bearings and distributor gears when press is too high (that expensive and fragile aluminum front cover), so I thought this would be of interest to them.
On my factory picture of the LA pump, it looks like there are spots on the body that could be drilled and tapped for a small screw (for control and test) that would dump oil from the passage right into the pan (in addition to the relief port back to the inlet side).

Wouldn't it be nice to figure this out?
Area of 3/8" hole = 4 X area of 3/16" hole (Pi R^2), but the smaller one won't flow the whole 25% due to Poiseville flow, skin effects, etc.

I wonder if the area of the valve passage is larger than the relief passage back to the inlet. If yes, then drilling or porting that passage will definitely help. I wonder if a new slightly larger valve could be made or borrowed from another motor - the only really important factors are OD, length and spring pocket ID. More thoughts: the LA pump appears to be referenced to inlet pressure (supposedly the best method). Inlet pressure should be affected by crankcase pressure, though - the whole system is inside the pan (unlike a B or Buick). ejit

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Good discussion here. Having the bypass go back to the inlet is a very good idea in any kind of pump that has difficult inlet conditions, and lifting cold oil up a small tube through a screen difinitely qualifies as difficult inlet conditions. By running the bypass back to the inlet, you reduce the amount of oil that is needed to be lifted to the pump, and thus reduce suction vacuum, which reduces the likelyhood of cavitating the pump, or sucking a hole in the oil in the pan and sucking air.

I think there are several kinds of ports around the valve to the inlet, from slots, to reliefs, to ports. I did check the area on mine when I ported it, and they were of adequate size.

I think the most likely to be the problem are (in this order)-coil bind from a bigger wire diameter spring or shimming the spring--burrs or flash limiting the travel of the valve,--blocked or too small bypass passages--too stiff a spring to open all the way.

If I were to go after a problem, I think I would address all of them and be sure. booster

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Alright then add another Q to the fire. What is the average burst pressure of a typical oil filter? I use the 3614 part number in Walmart brand or alot of times in Quakerstate brand. It has been my understanding that these smaller filters typically have a higher burst strength than the larger sized filters.

I found that most of the standard types-Fram etc- would start to stretch at the base at about 100 psi and start to leak from the seal at about 110. Never did blow one off or apart, but had lots of leakers.

So why not use a block heater to keep your oil warmed up a bit?????....My 340 goes to 70 at the start up...no block heater....Or is this a dumb question?

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