"Hunting" oil pressure

Occasionally my oil pressure guage "hunts" or bounces at low rpms when idling or coasting. There doesn't seem to be any rhyme or reason to it; I cannot trace it back to temperature or how long it has been running. It will do it and then not repeat for weeks. I am running Castrol 20W-50 and a Purolator inverted filter. Pressure is good; about 60 psi cold and about 35-40 psi at hot idle. At 2500 rpm steady driving it is right at 50 psi.

If this car had an electric guage I'd just chalk it up to a funky sender or intermittent bad ground but this year has a mechanical guage.

Any ideas out there?

It isn't unusual for MGB oil pressure to hunt at low rpm, as long as it's steady at speed it's not a problem.

Clifton

Good, 'cause mine started doing it in hot weather too!

Mine does the same thing. remains strong and steady while driving, only huting at idle.
Clyde

Mine also does this occasionally at idle. Goes between 50 and 60 psi. I posted earlier about this. Folks said it could be a sticky pressure relief valve but not to worry.

Ditto. Mine does the same thing.

Great, thanks all - if it is a problem, lots of us are in it together!

I'm gonna' go hang around with Steve!

Here too. Perfectly normal on the mechanical guage. At one point during production, (its in the 'changes' part of Clausager's) a stint was added to the gauge to reduce the perceived issue. Wouldn't give it another thought.

Paul

With the standard oil cooler the oil temp rarely gets to optimum temperature. The hoses and fittings may feel quite warm but the stuff just doesn't get to the 190 or 200 degrees needed for full flash-off of moisture and other bad stuff. With the constantly cool temps the viscosity remains rather high so the pressure reads perhaps a little higher and more steady than it will if the oil gets fully warmed and therefore "thinner". At full operating coolant temp a B engine will reach its blow off valve pressure of about 75 pounds or so and stay there at most RPMs above say 25 hundred. At idle it might drop back to forty or fifty and pulse there just just a bit.

If you install an oil temp thermostat or shunt in the cooler lines, the cooler doesn't come into play very often. Until the oil reaches the 190 or 200 mark it is just re-routed back to the oil galleries without passing all the way out to the cooler. This will result in an average drop of ten or fifteen pounds across the board as the oil is heated to it's best operating temp. My B runs about 60 to 65 PSI and 35 PSI at 2500 and 800 REVS respectively. If I run the revs up to say 3500 or 4000 the pressure will reach back up to the 75 PSI range. This is with the cooler shunt installed.

All of this is completely normal. Lack of temp in engine oil is, IMHO, the single greatest factor in engine wear this side of repeated cold starts and short runs to the 7-11. There is something comforting about seeing that steady 75 PSI at the gauge but it isn't really necessary, and in some instances it is a false sense of protection.

Jack

Jack is right and I wish I had known this information earlier. I replaced both my blown-out oil cooler lines last year with the braided stainless lines. There is an oil delete kitI have often wondered if I should take a step down in oil weight, say to 10W-40, to accomodate the over-cooled oil. I know my thinking is botched here, but why?

That wouldn't' really fix the problem Bryan. In the earth time continuum it doesn't really matter, but if you want to take the plunge you can buy an oil thermostat off the net for about $60 or so and install it yourself.

Here is a URL for the brand that I got. http://www.batinc.net/thermos.htm The one that I have is the one in the upper left corner.

My hoses had been replaced at some point with armored hoses that were rated at 3500 pound, a bit of overkill to say the least, so they couldn't be cut easily and wouldn't compress well with stainless clamps anyway. I ended up cutting the compression collars off of the fitting ends and discarding the hoses. I reused the ends though by having the local parts house fit them to new hose by means of crimped collars as they do all the time for backhoes and heavy equipment. I think that the collars and labor were about $20.

Then I installed the whole shebang in the car. Once installed, I cut the new hoses with a knife in the appropriate places so that the thermostat could be spliced in just behind the radiator support diaphragm. I have one of the units that has the fittings as push-the-hose-on-over-swellings-at-the-end-of-the-metal-and-clamp-it.

There are other 'stats that come with real live screw on fittings but the pressures generated in the B oiling system are not all that high so I don't feel that it is necessary to spend the extra money.

Anyway, I used red (ugh) hydraulic return line, 1/2" ID, rated at 300PSI for the hoses., My 'stat is preset at 180 degrees F. You can get higher temp ones but I don't think that is called for in this particular use.

Jack

Jack...you are correct on oil temps I have a oil temp gauge and it is amazing how long it takes the oil to get to about 180 with the cooler in place and thats in Houstons 100 degree weather

I was just reading something in the Burgess book last night about oil temp and engine wear. Peter doesn't go into much detail about it but his observation is that the cooler might look good but it contributes to excessive engine wear in most climates unless a thermostat is installed.

I suppose that if you are just plain hooked on pressure the thing to do would be to use straight 50, but then you would have the wear problem of slow deliver on cold fire up.

I also noted a passage in one of my references about pulsing idle pressure due to poor seating of the relief valve slug. I hadn't thought about that but it makes sense. Unfortunately you can't lap the plug in unless you have the whole engine down and stripped because of the need for meticulous cleaning afterward.

Jack