Dropping oil pressure in new engine......

[KTL]

WHat's the mechanical gauge say about the pressure? I'd feel more comfortable testing with the finer resolution of a 60 psi mechanical gauge in the oil pressure warning light location.

[Porshaah]

It seems to me from the information you provided that the engine appears to be getting warm quite quickly (i.e. 180 degrees F in 1 to 2 minutes and/or 2 miles)

One of the things that contributes to a loss in oil pressure along with heat - loss of oil viscosity is if bearing clearances increase. For the oil pressure to drop that quickly (i.e. 1 to 2 minutes) the only thing I can think of that will change that quickly is an aluminum bearing as in the cam towers. Have you had a look under the valve covers to see if oil is getting in there and just a general inspection?

[Walt Fricke]

As I recall, gauges through the end of the 2.7s were 10 bar gauges, and required a 10 bar sender.

The SCs (at least those from '80 on) had a 5 bar gauge, and a 5 bar sender.

Using a 5 bar gauge with a 10 bar sender would give you about a half reading.

Using a 10 bar gauge with a 5 bar sender would give you about a double reading.

The increase in resistance of a 5 bar sender for each unit of pressure increase is double that of a 10 bar sender. The rheostat construction of these senders means they should be pretty linear, though I have not pondered their internal geometry to see how that might affect linearity. But no matter, gauge and sender have to match.

But do I recall that you checked all this by using a mechanical pressure gauge at one point? That would have ruled out sender and gauge quirks.

A used car salesman once solved the low oil pressure in a used car I was buying by putting in a new sender. Alas, the sender was for a 6 volt system, and this car had a 12, so the instant improvement in gauge pressure was illusory as far as car life went - a month or so later it threw a rod.

[fred cook]

Originally Posted by Walt Fricke

As I recall, gauges through the end of the 2.7s were 10 bar gauges, and required a 10 bar sender.

The SCs (at least those from '80 on) had a 5 bar gauge, and a 5 bar sender.

Using a 5 bar gauge with a 10 bar sender would give you about a half reading.

Using a 10 bar gauge with a 5 bar sender would give you about a double reading.

The increase in resistance of a 5 bar sender for each unit of pressure increase is double that of a 10 bar sender. The rheostat construction of these senders means they should be pretty linear, though I have not pondered their internal geometry to see how that might affect linearity. But no matter, gauge and sender have to match.

But do I recall that you checked all this by using a mechanical pressure gauge at one point? That would have ruled out sender and gauge quirks.

A used car salesman once solved the low oil pressure in a used car I was buying by putting in a new sender. Alas, the sender was for a 6 volt system, and this car had a 12, so the instant improvement in gauge pressure was illusory as far as car life went - a month or so later it threw a rod.

I checked the part number on the sender and it is indeed the correct one for the 5 bar gauge. Thanks for the input! At this point, I'm trying to not overlook anything.

[fred cook]

Originally Posted by Porshaah

It seems to me from the information you provided that the engine appears to be getting warm quite quickly (i.e. 180 degrees F in 1 to 2 minutes and/or 2 miles)

One of the things that contributes to a loss in oil pressure along with heat - loss of oil viscosity is if bearing clearances increase. For the oil pressure to drop that quickly (i.e. 1 to 2 minutes) the only thing I can think of that will change that quickly is an aluminum bearing as in the cam towers. Have you had a look under the valve covers to see if oil is getting in there and just a general inspection?

When I reassembled the engine, I used a different set of cam housings. However, I did check the cam bearing bores and saw nothing that would indicate any wear or damage. When I start the engine and simply let it idle, the oil pressure does it's trick before the oil gets hot. While the oil is warm, nothing (except the header pipes) is too hot to touch. On the second drive, I went a bit over 2 miles and the oil temps were just starting to show on the gauge. I have not pulled a rocker cover, but don't hear any improper noises from the valve train. Checking under a cover is a good idea, will probably do that next.

[fred cook]

Originally Posted by KTL

WHat's the mechanical gauge say about the pressure? I'd feel more comfortable testing with the finer resolution of a 60 psi mechanical gauge in the oil pressure warning light location.

Kevin,

The mech gauge confirms the dash gauge now that it has the new sender. Since they matched up, I pulled the mechanical gauge and reinstalled the gauge sender.

[thumbdoctor]

Have you checked the oil pressure at various points along the oil system. I had to drill and tap a oil bypass plug (screw)and tap it (1/8 pipe thread) remove the plunger piston and verify oil pressure there to diagnose internal oil pressure leak. Another check would be to temporarily block the supply to the cam housings/chain tensioners and retest pressure.

[Lapkritis]

I'd be paranoid of cooking a cam/housing.

[Walt Fricke]

Fred - Oh, how well I know that feeling.

When having difficulties with things I don't understand well, I don't feel too badly (frustrated, but not stupid). Not the same where I have a decent handle on things and they still won't work.

[dtw]

Sorry for the Captain Obvious question, but in the spirit of assuming nothing, and since the cam housings were swapped out...are the cam spray bars present and accounted for?

[fred cook]

Originally Posted by dtw

Sorry for the Captain Obvious question, but in the spirit of assuming nothing, and since the cam housings were swapped out...are the cam spray bars present and accounted for?

Yep, all present and accounted for! Good thought though! Appreciate the input!

[fred cook]

Originally Posted by Walt Fricke

Fred - Oh, how well I know that feeling.

When having difficulties with things I don't understand well, I don't feel too badly (frustrated, but not stupid). Not the same where I have a decent handle on things and they still won't work.

I guess at this point, I am more disappointed than anything else. If the problem is due to a less than perfect seal, that's someone else's fault. If the problem is due to a bone headed mistake on my part, well that's another story! In either case, it will be my labor that straightens things out. Perseverance is the name of the game!

[Henry Schmidt]

Hi Fred
I've been watching this thread for a while and hoping you would find something obvious.
It seems you haven't.
I've seen this very same problem in a fresh rebuild that had crank work. The crank was heat treated / nitrided without replacing the crank plugs. Shortly after restart, a crank plug fell / blew out. Heat treating caused the aluminum plugs to expand and as the crank cools they get loose.
I've also seen crank shops replace aluminum plugs with threaded steel allen plugs and installed them loose so the builder could clean the crank. Not knowing they were loose the crank gets install with loose plugs.

One other thought. We had a race engine years ago that threw a rod and during the explosion the rod hit the case and put a small whole in the case right into the oil galley. hard to see but if we had used it my guess would have been, low oil pressure.
Good luck.

[MetalDoc]

Hi,

I have been watching this thread for a while wondering what the low oil pressure problem is. Is it possible the input side of the pump is restricted somehow? When you first run the engine the oil pressure is okay, but then after it warms up the oil flow to the input of the pump is restricted and not enough oil is running through the pump to keep up the pressure. Is there any way to measure the flow from the oil reservoir to the high pressure side of the pump?

Paul

[fred cook]

Originally Posted by Henry Schmidt

Hi Fred
I've been watching this thread for a while and hoping you would find something obvious.
It seems you haven't.
I've seen this very same problem in a fresh rebuild that had crank work. The crank was heat treated / nitrided without replacing the crank plugs. Shortly after restart, a crank plug fell / blew out. Heat treating caused the aluminum plugs to expand and as the crank cools they get loose.
I've also seen crank shops replace aluminum plugs with threaded steel allen plugs and installed them loose so the builder could clean the crank. Not knowing they were loose the crank gets install with loose plugs.

One other thought. We had a race engine years ago that threw a rod and during the explosion the rod hit the case and put a small whole in the case right into the oil galley. hard to see but if we had used it my guess would have been, low oil pressure.
Good luck.

Henry,

Thanks for the input. In the case of my engine, little was done to the crankshaft as it measured well within the standard range with no surface defects, taper or other signs of wear. The bearing shells that were removed were standard bearings with virtually no wear. Only the face of the thrust bearing showed any signs of wear and that was very slight. I have owned this car for over 15 years and 60k miles so I am certain that there were no issues there. On the other hand, a plug could have worked its way out. The only way to tell is to tear down the engine again. Actually, at this point, I am becoming more suspicious of the culprit being an improperly made oil seal. Specifically one of the oil pump seals. Again, only a tear down will tell. I have decided to let things sit for a day or two before undoing all the work. At least the parts will all be clean and easy to remove!

[fred cook]

Originally Posted by MetalDoc

Hi,

I have been watching this thread for a while wondering what the low oil pressure problem is. Is it possible the input side of the pump is restricted somehow? When you first run the engine the oil pressure is okay, but then after it warms up the oil flow to the input of the pump is restricted and not enough oil is running through the pump to keep up the pressure. Is there any way to measure the flow from the oil reservoir to the high pressure side of the pump?

Paul

I checked, nothing in the sump (shop rag, etc.) that would cause problems. Thanks for the thoughts.

[MetalDoc]

Hi Fred,

Is the high pressure side fed from the sump or the oil reservoir? I was looking at the diagrams in previous posts and it appears there might be two lines from the reservoir. Right now my engine is not in the car, so I don't know. Also, I am no expert.

Paul

[fred cook]

Originally Posted by MetalDoc

Hi Fred,

Is the high pressure side fed from the sump or the oil reservoir? I was looking at the diagrams in previous posts and it appears there might be two lines from the reservoir. Right now my engine is not in the car, so I don't know. Also, I am no expert.

Paul

The oil pump picks up oil from the sump and pumps it to the filter and then into the oil tank. From there, it uses gravity feed to run back to the pressure side of the oil pump via the "S" hose. At the pump, the oil is pressurized and sent thru the engine to the crankshaft and eventually getting sprayed on the cams and rockers. From there, the oil drops back into the sump to start the trip over again. In the SC engine, the oil pressure relief valve has approx. a 5 bar opening pressure and the oil pressure safety valve has an approx. 8 bar opening pressure. The oil pressure light sender and the relieve valve are served via the same vertical path and the oil pressure gauge sender is on the far end of the oil path getting it's pressure just before the tensioners and the camshafts. So, a blown seal in either of the tensioners could cause the overall oil pressure to appear to be low when it might actually only be low at the end of the path. Or, a poorly seated or incorrectly made oil pump seal could be the culprit. Or, one of the plugs in the crankshaft could have fallen out. Lots of possibilities at this point. Unfortunately, most will require taking the engine back apart to try to find the problem.

[sjf911]

It was Chris at TurboKraft with Linc's build that had this same issue with a VR gasket set: Project 930 The Resurrection

That is why I went with a Wrightwood set on my rebuild.

[fred cook]

Originally Posted by sjf911

It was Chris at TurboKraft with Linc's build that had this same issue with a VR gasket set: Project 930 The Resurrection

That is why I went with a Wrightwood set on my rebuild.

I just went over and read this thread. That is just what my engine is doing, although with slightly different numbers. I have a set of seals coming from a different source that have proven to be correct. Sounds more and more like I've got another build coming!