Oil Pressure Issue at startup

[SpyderMan]

Recently I have noticed that when I am starting my wagon as soon as I start cranking the oil light goes out as it instantly is building pressure but as soon as it starts the light blinks back on and goes out a second later. I had a gauge on the engine when I first got it started after it was apart for a failed cam gear, the oil pressure was fine. Any reason it would loose pressure for a moment once started?

I am going to put the gauge back on to verify but I don't think the dummy light is lying. Once it is running I don't seem to have any issues even idling in gear while hot, 600 RPM on a 90deg day. Not a flicker. Any ideas?

[joelsplace]

I can't see any way that could happen with the oil pressure. I'll bet it is something in the switch or wiring.

[66vairguy]

When my 66 Vair sits awhile I notice the oil light does not go out until just after the engine starts. To clarify my engine usually starts quickly. Just me --- others can comment on what they observe.

While the starter is engaged the oil pressure warning light is dimmer due to the voltage drop when the starter is engaged.

Note the oil pressure switches are known to fail. You might just try replacing it before taking things apart.

[SpyderMan]

I will get a gauge on it but a am quite sure I am actually loosing pressure. I am getting lifer rattle wen the light comes back on and my lifters go silent as soon as the light goes out.

[vairmech]

So how long does the light actually stay on after starting?

I think you need a direct mechanical gauge right at the oil pressure switch hole, no small lines, not electrical. Then you can do a remote start and watch the gauge in the back. Then you can make an oil pump tool from an old distributor, remove your distributor put the tool in and see if you can physically feel the lesser pressure.
PLEASE, do not just try to use a screwdriver, that hole down there is an unprotected bearing area for the distributor shaft.

Here is how I do my test run pressure gauge. 1/8" pipe about 6" long with a gauge coupled to it.

[jimbrandberg]

I've had some weird things happen with oil pressure if the piston and spring thingy that is accessed through the side of the rear housing is not operating freely. Sometimes not enough oil pressure and sometimes too much.
I don't know if it's your problem I just throw it out there for consideration.
If it is not operating freely it's tough to get it out of there. I wondered if it's stainless but a magnet does stick to it.

As one example, I had an engine this Winter I was testing on a cart that had poor oil pressure when cranking but seemed okay once the engine started. I usually turn it over with the starter until the light goes out before connecting the ignition but I cranked and cranked and it never did go out until the engine was running. It had a high volume oil pump and I thought maybe someone had a thick gasket in there or something so I replaced it with a stock oil pump. When I started the engine again it blew out the oil filter seal. I fished out the piston and cleaned the bore and the oil pressure seemed okay. The engine had low compression in a cylinder or two so I put it back in storage for now so I don't have a long term story about it. I was only using a light so I don't have any real numbers either.
It's a 180 turbo engine with 140 heads that someone "rebuilt" a long time ago. They didn't do an oil return so it's a bit of a project one of these days. I finagled a pair of Rochesters and 110 exhaust on there for testing.
But I digress and that's all I have to say about that.

Jim Brandberg
Isanti, MN
CorvairRepair.com

[66vairguy]

I've taken apart engines and seen the same thing Jim mentioned - the oil pressure regulator piston was "sticking" due to grimy sludge packed in the piston hole the spring sits in. A basic cleaning and the piston moved freely.

I'll add that at one time many said you should "stretch" the oil pressure regulator spring on an old engine since they loose tension. THAT IS NOT CORRECT! Between myself and a few others we tested about 20 USED oil pressure regulator springs in a jig I built (like a valve spring tension tester). NOT ONE WAS OUT OF SPECIFICATION!!!!

If in doubt test it, but don't just stretch it to increase tension (and oil pressure).

BTW the high volume oil pumps do keep the oil pressure piston open farther since they supply too much oil flow except on loose bearing tolerance race engines. Years ago a magazine (Hot Rod?) tested a high volume oil pressure pump in a big block Chevy engine. They found the engine oil temperature was HIGHER!!! They consulted the experts and found the excess oil volume was by-passed back to the engine sump by the oil pressure regulator (to keep oil pressure within specification - yes too much oil pressure is not good for the bearings). The HIGH VOLUME OIL PUMP was heating up the oil due to mechanical energy (bigger oil pump gears) that was basically wasted energy since the oil pressure regulator was routing the oil back to the pan!

This is an example of why assumptions need to be tested.

[SpyderMan]

Thanks for the suggestions from everyone. I do not have a setup for reading pressure at the sender but I do have my drilled oil filter bolt so I will try it first and see what I get. I took it off before this started happening when I installed a 90deg adapter in anticipation of an AC pulley. Now that I think about it that is when I started having the issue. It has a stock oil pump that I checked tolerances on when I had the motor apart last year. I think I had the pressure spring assembly out and everything looked and moved ok. I also have a gutted distributor I use for priming engines so I could do some experimenting with it if needed. I will swap the oil filter setup so I can put my gauge on and report back. Thanks again.

[azdave]

I'll add that at one time many said you should "stretch" the oil pressure regulator spring on an old engine since they loose tension. THAT IS NOT CORRECT!

I 100% agree that it is not correct to stretch that spring but that's due to a reason you don't mention.

Stretching that spring does absolutely nothing to improve a low oil pressure condition. It only serves to increase the MAXIMUM oil pressure limit that you'll see when the oil is cold and thick. Stretching that spring can lead to blowing out gaskets and swelling your oil filter like a balloon during the first start of a cold day, especially if you rev-up the engine right away. It does absolutely nothing to help increase oil pressure at low RPMs. There are no springs or regulators in the oiling system to help overcome a low oil pressure problem but choosing the proper oil pump housing selective gasket is important as you assemble an engine.

If your engine is so worn out that you cannot maintain hot idle oil pressure, a change to a high-volume pump would mask the issue for maybe a few more years if you are lucky. If you do run a high-volume pump, you should open up the relief valve bypass hole in the front cover to handle the excessive flow (cold start) that the relief valve will be looping back to the oil pump intake port.

I'm 99.9% sure the OP has a bad $8 oil pressure switch but lots of good tips all around.

[66vairguy]

I'll add that at one time many said you should "stretch" the oil pressure regulator spring on an old engine since they loose tension. THAT IS NOT CORRECT!

I 100% agree that it is not correct to stretch that spring but that's due to a reason you don't mention.

Stretching that spring does absolutely nothing to improve a low oil pressure condition. It only serves to increase the MAXIMUM oil pressure limit that you'll see when the oil is cold and thick. Stretching that spring can lead to blowing out gaskets and swelling your oil filter like a balloon during the first start of a cold day, especially if you rev-up the engine right away. It does absolutely nothing to help increase oil pressure at low RPMs. There are no springs or regulators in the oiling system to help overcome a low oil pressure problem but choosing the proper oil pump housing selective gasket is important as you assemble an engine.

If your engine is so worn out that you cannot maintain hot idle oil pressure, a change to a high-volume pump would mask the issue for maybe a few more years if you are lucky. If you do run a high-volume pump, you should open up the relief valve bypass hole in the front cover to handle the excessive flow (cold start) that the relief valve will be looping back to the oil pump intake port.

I'm 99.9% sure the OP has a bad $8 oil pressure switch but lots of good tips all around.

You are correct Dave. I didn't want to over do it with the text, but your addition is worthwhile and YES many think that stretching the spring will fix a low RPM oil pressure problem, when in fact it is worn out bearings that cause low RPM oil pump flow to be inadequate to maintain pressure. Some race engine are built with large bearing tolerances to reduce HP loss and this is when a high volume oil pump is needed, but this is mainly done on drag race engine that are see low miles between rebuilds.
Thanks again for the comments.

[bbodie52]

» Sun May 19, 2024 8:57 pm

Recently I have noticed that when I am starting my wagon as soon as I start cranking the oil light goes out as it instantly is building pressure but as soon as it starts the light blinks back on and goes out a second later. I had a gauge on the engine when I first got it started after it was apart for a failed cam gear, the oil pressure was fine. Any reason it would loose pressure for a moment once started?

I wonder if your observation is truly indicating oil pressure activity. It could just be an electrical anomaly. When you turn the key to ON, power is applied through the switch from the "R" (12R Wire) battery source to the "C" (14DG Wire) to the harness junction point. This normally applies power to all of the wires tied to that junction, including power to the TEMP/PRESS indicator lamp (as a bulb test). When you rotate the switch to START, power is applied from the ignition switch "S" terminal to the starter solenoid "S" Terminal via the 12V (12 Gauge Purple, or Violet wire. THIS ENGAGES THE SOLENOID TO CRANK THE ENGINE, AND ALSO APPLIES DIRECT 12 VDC FROM THE SOLENOID "R" terminal via the yellow wire, to the ignition coil positive terminal to power the coil while the engine is being cranked.

I am not certain about the ignition switch internal connections. But it may be that the power from the switch "C" terminal is momentarily interrupted while the engine is being cranked. This interruption could disrupt power to the TEMP/PRESS bulb during engine cranking, but power to the bulb would be restored when the engine starts and you release the key back to the ON position. This would cause the bulb to come back on, as long as there was no oil pressure reaching your oil pressure switch. A moment later, oil pressure would reach the pressure sensing switch, which would turn the bulb back off as the switch GROUND was disconnected by the presence of oil pressure.

You are interpreting the bulb going out when you crank the engine as an indication of the engine "instantly building pressure". But instead, it may only be an interruption in bulb voltage as it is disrupted by the switch rotation to the START position. The ignition system still gets power directly from the starter solenoid as long as the solenoid is engaged with cranking the engine — but the oil pressure warning bulb may only have gone out because you rotated the ignition switch to START. If this is the case the initial bulb outage may only indicate a lack of voltage from the ignition switch. When you release the spring-loaded switch as the engine starts, power is then restored to the bulb so it can indicate the presence of oil pressure. A moment later, the actual engine oil pressure hits the oil pressure switch, removing the switch ground and extinguishing the illuminated bulb as oil pressure reaches the switch.

[joelsplace]

If the spring is in good shape stretching it will not help low rpm oil pressure but if the spring is too short stretching it will fix low rpm oil pressure. I added a ball to one and it fixed low oil pressure at idle. I'm guessing the spring was too short to keep the valve closed at idle but I didn't have another one handy to compare.

[SpyderMan]

Small update. I removed the 90deg adapter and installed my gauge. I lost some oil in the filter so I cranked until I got pressure, I will test in the morning when it has been sitting over night. I did start it and I had 40psi at idle and 60psi with a rev.

As I said before when the light comes back on I get lifter clatter that goes away as soon as the light goes out. I really don’t think it is an electrical bug.

[vairmech]

Finally some real numbers! With your 40-60 psi reading you don't have an oil pump problem.

As a note to the others mentioning anything high volume oil pump, don't. If you would just put a new standard oil pump in and set it up properly, not like Clark's say, even with the original spring you should have at least 10 psi hot at idle on all but the most worn engines. If the engine is that worn so you still don't have oil pressure then you should be hearing some pretty odd noises in the engine.

And those mentioning a stuck pressure relief valve that will cause extremely high oil pressure not a low oil pressure. IF there was a chunk of grit causing the valve to stay open, then the oil pressure would be low especially at idle.

Just a little note, I have forgotten to put the plugs in the ends of the oil galleries, I still had 20 psi showing on the gauge at speed but at idle , yup, nothing!

[SpyderMan]

I am going to have to check the pressure at the sender as Ken suggested. The hot idle is concerning the light was off as it said it had no oil pressure. It sound perfect healthy when running and driving.

[66vairguy]

Just a little note, I have forgotten to put the plugs in the ends of the oil galleries, I still had 20 psi showing on the gauge at speed but at idle , yup, nothing!

You won't be the first one to do that!! One reason I always test a rebuilt engine BEFORE I install it in the vehicle.