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Low oil pressure

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rovernut

rovernut

Jedi Trainee
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Have Dads 74 1/2 Mgb GT up and running now with the new motor but the oil pressure is dangerously low i feel.......It starts up at 50-55 lbs and as it warms gets down to say 15........I know it is a new relief pressure spring in it and the oil pump is from his old motor which never gave him oil pressure trouble........Any other things i should be looking for.........I tried putting the pump in a pail of oil and hooking it up to a drill to see if it pumped good but it never did pump what i thought it should..........Only gurgled up a little /ubbthreads/images/graemlins/nopity.gif /ubbthreads/images/graemlins/canpatriot.GIF /ubbthreads/images/graemlins/confused.gif
 
It sounds like to me that you know what the problem is...the pump...but are looking for an easy out??? /ubbthreads/images/graemlins/nopity.gif

Sorry, I have to agree here...it sounds like a bad pump. Replace it and you will have some peace of mind anyhow. /ubbthreads/images/graemlins/driving.gif

Bruce /ubbthreads/images/graemlins/cheers.gif
 
You say this was a rebuilt engine. Did you rebuild it? What about rod bearing and main bearing clearances. Did you check those with plastiguage?
Also I read somewhere that the stronger the spring on the relief valve, the lower the oil pressure will be. Some have made the mistake of stretching the spring and that makes the pressure lower. You can try finding a washer to fit the end of it so it won't go in as far and see if that raises the pressure.
 
I just looked in my Bently manual and it says the correct oil pressure is not below 50lbs at normal road speed and not below 15lbs at idle.
 
According to the book it says if the oil pressure is low the pressure relief spring is weak so putting a new one in should raise the pressure i would say......The engine has all new bearings, thrust washers, etc but no i did not check with plastigage........Why would that alter the oil pressure..........I,m assuming the pump is at fault but it worked right in the other motor.......I don,t recall him saying it ever dropped below 50 when running or idle but i,m not sure..........This car is more trouble than my Rover's have ever been but i've learned a lot /ubbthreads/images/graemlins/canpatriot.GIF /ubbthreads/images/graemlins/driving.gif
 
Hi, RN -

Shot in the dark: Maybe your oil pressure gauge is off. You might want to hook another up to it, just to be sure.

Also, the plastigauge would tell if the clearance between the journals and the bearing surfaces are correct. Too much "air" between them will lower the pressure. Here's the way I relate it (though proper engineers may call me on this!): Think of a water hose, as you restrict the channel the water goes through, the pressure builds up. When the surfaces of the journals and bearing surfaces wear, pressure drops.

Mickey
 
rn:

Low oil pressure can come from a worn pump but it can also come from loose internal engine clearances. If your car has new bearings but a worn crank, the excess clearance will allow low oil pressure, no matter how good the pump is.
By all means, check the gauge. If pressure is truly low, then you may want to replace the pump. But while you have the engine oil pan removed, you should check rod bearing and main bearing clearances. Using Plastigage is fairly easy and reasonably accurate for this purpose.
 
with risking sounding like an idiot - what kind of oil did you use? my car had the same prob and i put some heavier oil in and it solved the prob. . . . since you only have low pressure when it's hot, that could be it, as oil loses it's viscosity with heat.
 
Rovernut, I like Mickey's advice about the gauge. I had the same problem, it was the gauge. Seen it in other LBCs as well. The gauges in these cars weren't up to today's standards, and they're pretty old, too.

Maybe you'll get lucky and it IS only the gauge. It's always a thrill to encounter an easy (and cheap) fix!

good luck!
 
Hmmm...got me to thinking, Mark. My fresh rebuild shows well over 60 lbs. of pressure on the old gauge. Wonder if I ought to cross-check it?

Human nature being what it is, I suspect we would trust a gauge that shows us what we want to see more so than one which disappoints us!

Mickey
 
Your oil pressure should be just fine. Mine runs at exacty the same thing, 50-55 at acceleration, and 15-20 at idle. I drive mine every day.
 
Alot have said they're oil pressure is like this but it was higher with the old motor..........He's ordered a new pump and we'll see what we get .......Thanks
 
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