oil pressure guage or sender

[carolinamv]

When I start mine im at 20PSI-25PSI tops, it stays there just about the whole time im driving my truck. Any quick things to look for if this isn't normal.

[MSeriesRebuild]

Run a compression test before spending $$ looking at other things. This will expose any internal issues going on within, and give you a definite direction to pursue any needed maintenance or possible rebuild issues. I always advise the compression test first because more often than not, this will bring to light issues not seen or suspected. Long story short, many times such issues as low oil pressure are possible indicators that a rebuild is in the near future. A compression test will let you know the score in just a few minutes. If test results are good; then you can look closer at possible reasons for low oil pressure.

[carolinamv]

My problem is im having problems with a few gauges, oil pressure gauge wrong , temp gauge not reading, and fuel gauge reading max when you tap on it (tank is full though).

The only working gauge when I bought the truck was the battery and speedo. This truck was museum quality 100% restored motor and all , frame off ,a few years ago , new wiring ,etc. then the former owner let it sit in a horse barn for a couple years.

The oil pressure gauge was the 120 type, when it was in it would barely read at all. I replaced with a 60 psi type. Now it reads 20-25PSI when you crank the truck. It just reads 25-30 psi all the time.

Im no wiring type of person so im new to this. If I had someone local to learn from or pay and watch them to learn it would be nice.

[MSeriesRebuild]

My suggestion now is that you make sure you have a 60 PSI sending unit instead of the one that would have been correct for the 120 gauge you said was installed. Each gauge requires a compatible sender to offer correct readings. A way to double check the electric gauge is to install a mechanical type gauge just to verify the reading. If that doesn't show you verification that your gauge is reading incorrectly; then we are right back where we started in my mind, in which case I'd still recommend a compression test to verify the condition of engine internals.

I'll be the first to admit I have no idea concerning the credibility of the info offered to you about a museum quality restoration; however being many years in the restoration business and knowing full well the cost involved in restoring a M37 to museum quality; it will be hard to convince me that someone spent that kind of $$, then would let the truck sit unmaintained in a barn for a few years. First off, the type of restoration you are claiming would have never had an incorrect 120 PSI gauge installed. This is beginning to scream RED FLAG to me. Now obviously I hope you can prove my suspicions wrong; if I can help further, please check out my website below, feel free to call or email us from there. I'm happy to try and help you get to the bottom of what is going on.

[carolinamv]

Thanks, my next step is t check the PSI with another guage like you said.

The person that restored it didn't let it set, the person he sold it to did.

It has all new wiring and a harness ,etc. But that doesn't mean a lot.

[ZGjethro]

My truck is a 1952 model with a replaced 60 psi gauge. I get 30 psi at idle, and it raises to 40 at high sustained revs. What factors would result in low oil pressure? Clogged lines? Old pump? Leaks? I ask since I have a pretty good oil drip at the oil pump and I was going to pull it and replace the gaskets. All the bolts seem tight. If a new pump would boost pressure, I'd spring for one. Oil is 15-40 Rotella and the truck lives in a heated garage.

[MSeriesRebuild]

If your engine has 40 PSI after warm up, that is very normal for the average engine. The drip should certainly be fixed as soon as possible; that would be either at the gasket where the pump base mates with the block or the pump cover plate o-ring. The o-ring is square cut, so that has to be the right part to replace it, a standard round o-ring will not work. The cover plate should also be surfaced when removed to replace the ring; this will help restore the oil volume that the pump is capable of delivering.

Slight drips don't cause pressure loss. Most common place for noticeable pressure loss is cam bearings. Since special tooling is required to replace those, many times old cam bearings don't get replaced during amateur rebuilds because necessary tooling is not at hand. In severe cases, there will likely be issues such as slight skips, pops, and hesitation caused by erratic valve action as bearing wear becomes sufficient to allow the cam to lift and jump around a bit. Main and rod bearing wear also causes pressure loss. Even slight wear in all these areas will show significant pressure drop when the oil warms up good. If your reading is good at cold start up, then drops significantly below normal after warm up, most likely bearing wear in the areas mentioned is what you have going on.

[ZGjethro]

Thanks Charles. It goes to 30psi almost immediately, and will stay around that mark until the revs climb. The pressure is pretty steady with no fluttering. It gradually increases or decreases based on engine speed

I think it is the pump cover plate o-ring which is leaking. I wiped it down after I changed the oil yesterday and at idle it started seeping again.

[MSeriesRebuild]

Thanks Charles. It goes to 30psi almost immediately, and will stay around that mark until the revs climb. The pressure is pretty steady with no fluttering. It gradually increases or decreases based on engine speed

I think it is the pump cover plate o-ring which is leaking. I wiped it down after I changed the oil yesterday and at idle it started seeping again.

I expect you are losing some volume capability as a result of that, be careful; if it were to blow completely, you will loose it all. Needs to be addressed promptly. As you described it, your pressure reading is normal and behaving exactly as it should.

[ashyers]

Charles,
Were would you suggest plumbing a mechanical gauge into the block? I'd like to verify the oil pressure in our M and possibly hook up a 20psi idiot light just in case.

Andy

[MSeriesRebuild]

Charles,
Were would you suggest plumbing a mechanical gauge into the block? I'd like to verify the oil pressure in our M and possibly hook up a 20psi idiot light just in case.

Andy

Fine to use a mechanical gauge for verification of accuracy. I'm not a big fan of using mechanical gauges solely, simply because it is simply another source of a possible leak. Anytime you can get around using external tubing, hoses, etc., you reduce the risk of accidental oil loss in the event a hose/tube failure did occur. Using a gauge that works properly with an electronic sending unit does away with a leak possibility in that sense. Adding a sensor to operate a warning light if pressure drops is a great idea.

[Elwood]

Charles,
Were would you suggest plumbing a mechanical gauge into the block? I'd like to verify the oil pressure in our M and possibly hook up a 20psi idiot light just in case.

Andy

You can plumb a mechanical gage into one of the four openings for the main bearing web oil passages that are drilled from the left side of the block through the main fore and aft oil passage. Some of these are already in use, e.g. the front one has the elbow for the oil filter feed line, so you'd need to add a "T" fitting if you want to keep the filter in the loop while you have the mechanical gage connected. If a passage is not in use, it should just have a square head 1/4NPT pipe plug. If I remember (I'm not in the shop as I'm typing this), the rear main web cross passage plug is probably impossible to get to behind the starter.

In the illustration below, the main oil feed passage is the blue line (there are pipe plugs at either end where the passage was drilled through the block, but these are inaccessible when the engine is assembled). The red arrows indicate where the main bearing web cross passages are drilled in from the side.

[ashyers]

Elwood,
Thanks, that's just what I was looking for.

Andy

[MSeriesRebuild]

Thanks for taking up my slack; I replied to that at 4:30 this morning when out getting heat going in the shops, etc. I can add this to the advice; it's better to use a port that doesn't serve any other function. Teeing off of a constant flow line, such as the oil filter will show lower pressure than having the gauge working by itself from a dead end port. That was one of those hard lessons learned years ago around here.

[ashyers]

Charles,
Thanks, I'll take a look at the truck today during class and see what ports are accessible and unoccupied. Hopefully the pipe plugs won't be too tight!

Andy