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Too high oil pressure?


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I seem to have too high of an oil pressure. I though maybe it was because I used 20W50. Using SAE 30 brought the starting oil pressure down a little but it significantly right of the last mark on the oil gauge which is 50. Before this winter project, when the car first started, the oil pressure was in the guage area however I can't remember what it was. Tonight when I reeplaced the 20W50 with SAE 30, I only rean the engine for a few minutes as I didn't want to hurt anything.

What I did this winter was replace the oil lines to the filter, replace the oil line to the fitting on the cowl. Bought a replica oil filter. Mechanically to the engine I just did a valve job.

Any ideas? Other than that the engine seems smoother than when I started the project.

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I think I would tee in another gauge, somewhere under hood not behind dash, like maybe at the outlet of oil filter. If pressure is very low there then the filter lines may be blocked. Then you would need to check pressure at inlet to oil-filter and see if it matches dash gauge.

If second gauge reads high also, at inlet, then look for a restrictive fitting or blocked filter. Some filters come with a fitting that reduces the amount of oil flowing thru filter and increases oil pressure of system. And maybe the fitting is not needed with your system or is plugged. The restrictive fitting is needed for Non-fullflow filter systems. (By restrictive-fitting, I mean one that has a very small hole thru it.)

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I don't think the filter fittings are the issue as I just bought standard flare fittings with pipe thread ends that screwed into the oil filter canister. The fittings were the same as used on the previous oil canister.

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Assuming the true pressure is too high and you know it's not due to new bearings being fitted too tight, I suggest you simply need to adjust the oil pump pressure relief valve. BTW, assuming your engine isn't running with largely excessive clearances and that you're just trying to eek a few more miles from it, and that you don't live near the equator, 20-50 oil is much too heavy. Check the owner's manual or service letters for your expected temperatures but generally straight SAE 30 or at most, 15W-40 would be a far better choice.

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I am running SAE 30 now in the engine. I plan to buy an oil pressure gauge and some fitting to try and determine if I have any restrictions.

I'm almost thinking that the thin line that runs from the T at the back of the engine to the cowl fitting could be the culprit as being a small tube not much would it take to block it off slightly.

The engine is in real good shape and we didn't touch any bearings over the winter, only a valve job.

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tbirdman</div><div class="ubbcode-body">

I'm almost thinking that the thin line that runs from the T at the back of the engine to the cowl fitting could be the culprit as being a small tube not much would it take to block it off slightly.</div></div>

The small line thru cowl is probably the one to oil-gauge in dash, so it doesn't need to be large, since it only needs pressure not volumn. If it was blocked then gauge would be reading low, not high.

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Sorry I don't recall where the 9th series oil pressure relief valve is, on the 11th seriesw it's external. If yours requires removal of the sump I can understand your reluctance, but the purpose of the adjustment is to limit the maximun pressure and I'd say 99% that's where you should be going. Loosen the locknut, back out the screw that bears on the spring that loads the plunger about 3/4 turn (?), and try it. You didn't say or I didn't catch it, are you saying your pressure increased after doing a valve job? I can't think of an explanation for that unless you replaced worn roller pins.

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Owen_Dyneto</div><div class="ubbcode-body">Sorry I don't recall where the 9th series oil pressure relief valve is, on the 11th seriesw it's external. If yours requires removal of the sump I can understand your reluctance, but the purpose of the adjustment is to limit the maximun pressure and I'd say 99% that's where you should be going. Loosen the locknut, back out the screw that bears on the spring that loads the plunger about 3/4 turn (?), and try it. You didn't say or I didn't catch it, are you saying your pressure increased after doing a valve job? I can't think of an explanation for that unless you replaced worn roller pins. </div></div>

First thing I want to do is to double check the dash oil gauge as Speedster suggested. The only think I did to affect the oil pressure was to run new lines and replace the replica oil canister with another one.

The valve job only consisted of grinding the valves and the seats.

I'm suspecting:

1. faulty gauge

2. blockage in the oil canister or lines

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OK seems like the oil gauge in the dash is off. With the new gauge I measured 50 pounds at cold. So I won't worry about it, just need to realize that I'm reading about 15-20 pounds high. On to the next problem. smile.gif

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OK, so I couldn't let things lay. I borrowed two gauges from a friend. Now I have 4 gauges and only two agree frown.gif

The guy who restored my gauges said to bring one of the external guages over and he would see how accurate it was.

I did on his suggestion run the car a while to get the oil real hot. When I did that, the oil pressure dropped to 35 lbs on the dash gauge. SO maybe the dash gauge is OK. I'll find out later this week when I get the external gauge that matches in the dash gauge measured for accuracy.

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35 is more normal but I don't think a change of over 50 to 35, after warmup, is Normal. None of my cars do that.

Could the pressure-relief-valve be sticking until it gets hot?

Where is the relief-valve located on the '32? Is it in a Y-valve at side or rear of engine? If so, could it have been damaged or changed when replacing the oil lines to it?

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For whatever value the comparison is worth, on my 34 Eight I've set the oil pressure relief valve to open at 50 psi. Years back I had it set a bit higher but the pressure had ripped open a reproduction L-6 full-flow oil filter cartridge so I cut it back. In cool weather the pressure at road speed will be about 50. In typical warm summer weather the road speed pressure is about 40, with hot idle at about 25. The mechanical gauges are of the "bourdon tube" type, consisting of a flattened, sealed-end spiral of tubing; as the pressure increases the tubing tends to want to straighten (unwind) which moves a gear rack across the pinion which rotates the needle. I don't believe any type of adjustments are possible.

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Speedster</div><div class="ubbcode-body">35 is more normal but I don't think a change of over 50 to 35, after warmup, is Normal. None of my cars do that.

Could the pressure-relief-valve be sticking until it gets hot?

Where is the relief-valve located on the '32? Is it in a Y-valve at side or rear of engine? If so, could it have been damaged or changed when replacing the oil lines to it? </div></div>

I believe the oil pressure relief valve is located under the crankcase. You need to remove about 6 bolts, remove a screen and then there is screw for adjustment.

People I talked with thought it was normal that until you get the oil warmed up, there will be a signifciant variance in cold and hot oil pressure.

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tbirdman</div><div class="ubbcode-body">I believe the oil pressure relief valve is located under the crankcase. You need to remove about 6 bolts, remove a screen and then there is screw for adjustment. </div></div>

Okay, so it's at the oil-pump, inside oil-pan. That's the way the '29 is also. The '37s is external, on left side of crankcase and much easier to adjust.

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OK found an external gauge that was accurate. It was measuring about 75 lbs at start up. I turn the oil relief valve screw about 2 turns conterclockwise as the maunal said about 5 lbs per turn. It now reads about 53 lbs at start up and down to about 35 when hot and idling.

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Motor's reference says 55-60 pounds of pressure at road speed is correct for 37-39 Super Eight, which is of course essentially the same engine as the earlier (Standard) Eight for which they quote at least 35 psi at 25 mph. They also note 50 psi on the 356 engine and 50 psi at 25 mph for the Twelve. The 1933 Service Specifications state "minimum 35 pounds" for all models. So to me 50+ cold start and 35 at road speed sounds about ideal, those are about the ranges mine has been running at for 40+ years.

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