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MG MGB Technical - 50 PSI... And Not Climbing

Hi,

I just got back from Helping my friend J Elliott from not removing his engine. Since I have been away for four days, I thought it might be a good plan to fire up the 73 BGT I have out front on my drive. It took about a minute to get it to start, which is understandable given the extreme cold. It sounded extremely rough for a second, and then was firing well on all cylinders under full choke.

I gave the accelerator a prod up to about 2500, and the oil pressure gauge stayed at 50PSI, which it normally sits. "strange" I thought. The oil pressure gauge pipe had been spotting a little oil recently, and I had a new one to put on. When I popped the bonnet, I saw quite a flow of oil from the pipe. I switched off and changed the pipe.

I then restarted the engine, and it caught after about a second. It sounded ok, but the oil pressure gauge stayed at 50PSI regardless of engine speed, perhaps even dropping slightly if the engine was above idle for any length of time.

I switched off again quickly, checked the oil pressure pipe, which is no longer leaking, and here I am now.

What do you think it might be, and how expensive will it be to fix?

Cheers,

Dave.
Dave Pothecary

Dave. Depending on how many miles, I find 50 PSI to be fine. The engine on my 68GT needs a rebuild, as it has for the last four years. It shows about 50 psi hot and about 25 at hot idle. Still runs fine and shows no immediate signs of failure. What did you have before changing the line? Les
Les Bengtson

It was running up around that mark. I just pulled the dipstick. The level is good, but the oil has got air bubbles in it. I'm running a fairly cheap 20W/50.
Dave Pothecary

Perhaps you have accidentally overfilled it and it is foaming from crank splash? If your dipstick really doesn't read true, it could allow you to overfill in some circumstances. Or you may simply have taken your initial reading after changing the oil before it all had a chance to run down into the sump. I have learned to wait about 15 min before taking that first reading after filling or after a run down the road. FWIW
Bob Muenchausen

Dave. Your statement of "but the oil has air bubbles in it" confuses me. You should not take great pride in doing this as it is not difficult to do. How do you know the bubbles are in the oil rather than a product of removing the dipstick? It would seem that there would always be some "foaming" of the oil as it drains back from being in the upper part of the engine. When you check the oil immediately after running the engine, there seems to be some foam on the upper part. When you check it some time later, the bubbles seem to have broken up and gone away. From what you are saying, you found a leak in the hose going to the oil pressure gauge, replace the hose and everything is the same as it was. Why do you consider this to be a problem? Les
Les Bengtson

Dave, if I understand your post, you mention extreme cold and I think that the heavy oil is sluggish to go through the orifice in the gauge (to eliminate pulsations). This happens on my '73 when it's cold and once warmed up, registers normally. Perhaps your "fairly cheap" 20W/50 oil is heavier at cold temps and froths as well.

Wayne
Wayne Pearson

50 is right at the bottom limit for running pressure, it should be 50 to 80. Idling according to the book is 15 to 25, but mine c0ld idles at 60, hot idles to 40, and only drops to 25 if stuck in traffic for a long time in hot weather. There isn't enough information here, what are the hot idle and running (say 3000 rpm) pressures as well as the cold? What does it normally register, if different to what it is now? If it *never* gets above 50 it could be a stuck relief valve or broken/weak spring. In very cold weather it can also take a few moments to get to a maximum on starting.
Paul Hunt

Have you bled the new oil line of air?
glg

Dave,

50 seems fine on a cold engine. Both mine start cold and quite sharply cut out at 60 psi which is the relief valve lifting. If very cold and as the revs rise they can drop to 50 or even less and I have presumed that this is due to pump cavitation. Hot running one reads 60 the other about 57. Both have new shafts & pumps. They hot idle at 40 and 30 respectively at about 800 rpm. 40/50 whilst running may indicate some degree of crank/bearing/pump wear but is more than adequate for any engine. I would start to worry if I were achieving 70/80psi only because of increased load on pump drive gears, timing chain etc.

Iain
Iain MacKintosh

I'm happy to hear that others beside me experience an oil pressure of about 25-35 when stuck in traffic and that their engines are fine. After listening to all these stories on eBay about oil pressure I thought my engine was ready to bite the dust. I can sleep better now :)

I get about 60-65lbs on the highway when hot and after being stuck in traffic.
Mike MaGee

I went back out and ran the engine up to temperature. Pressure was at about 55 PSI at 1000 RPM (The lowest it will idle, and then it still needs choke, but that's a cam issue). Up at 3500 it reads as 63 PSI, which I sustained for a minute. The engine is overfull with oil, six pints being added when the dipstick read minimum. It looks like some oil had ended up in the pistons, because the gas meter box, which is just behind the exhaust pipe, was black from the exhaust. After about 5 minutes the exhaust was cleaning that gunk back off the box.

Dave Pothecary

Dave,
I would check the oil again after the car sits for a while. By my reckoning, you are about 2 qts (4 pts)over-filled. I would put some paper on the garage floor under the engine, put your oil changing pan on the papers under the oil pan, and undo the drain plug and let some oil drain out, then screw the plug back in. Check the oil level again. I would repeat this process unitl the level is down to the max line. This will be messy for sure, but that what the papers are for! It beats driving with a crankcase that is overfilled.
Good luck! Craig
CP Perry

I'll try getting some oil out of the sump over the weekend, peoviding my fingers don't fall off from cold.

Cheers.
Dave Pothecary

"Six pints being added when the dipstick read minimum" Takes one pint to move from min to max. And yet you know about idle rpm's due to cam issues. And you're helping the guy who doesn't know where to put the engine crane? My sincerest apology if I'm wrong--but are you pulling our leg? Again, sorry if I'm out of line--just doesn't seem to add up and something on the line of a hoax was mentioned in a previous thread not too long ago.
Paul Hanley

It's a confusing issue. The car sat on my drive is not actually mine. I won't pretend to be an expert on cars, and there are some things I know, and some things I don't. Most of the stuff I know I've either read here or in other books and websites, and the difference between min and max on the dipstick is something I'd not come across up till now.

I'm not trying to pull anybody's leg, but I do appreciate the fact that my knowledge is extremely patchy.

Anyway, thanks very much for everybody's help. I really do appreciate all the great advice and information available here.

Dave Pothecary

Screw you Paul,

The crane thread was valid if you read it. No mention of hoaxes at all.

In the UK we don't have huge cars so our garages tend to be smaller than you yanks so lay off the sarcasm and don't bother ribbing us if it isn't warrented.

Dave and I are 22 with no background in cars and are just getting into this thing. Dave knows about the cam thing through speaking to people just as I am learning about using an engine crane through speaking to people.

Sorry if this seems hot headed but we just spent 4 days in the freezing cold (myself feeling unwell with a head cold), mostly on our backs on a concrete garage floor only to be told we're hoaxers by some guy whose first message was to say we were being unsafe for no good reason.

Yeah...it's all one big joke.

Cheers for the help Paul.

James

J Elliott

Ps..I agree with Dave, the information and help here is top notch and you are an extremely nice and friendly bunch of people.

Jame
J Elliott

You don't need to bleed the oil gauge line - 60 psi is 60psi whether it is in air, oil or a mixture. It can in fact be counter-productive and give you a slow gauge while trying to pressurise all that cold, thick oil through that tiny pipe.
Paul Hunt

Pps..my comments weren't aimed at you, Solihull Paul!!!
J Elliott

I must now partly apologise to Paul.

I've just seen a few other mentions to 'the trickster', though Dave and I aren't that person and I don't think our questions were at all strange, at least when you read the content :)

What is this green car business all about?

Curious..

James


ps. I've mostly been active on the midget forums as I bought a Midget over the summer whilst waiting for the parts for my GT to arrive (which took 2 months).
J Elliott

About the green car business. Green cars seem possessed, certain inflictions occur ONLY to green cars :) and to add, owners of green cars tend to be a bit strange.

BTW, Franky (my B) is BRG and just isn't tempermental at all. Must find something wrong with him soon, I miss posting on the board. Anyone agree with me that green cars (when they work) are actually the fastest?.
Luigi

I can't talk...my car is brown! :)

Thanks for letting me in on the injoke.

JE
J Elliott

JE,

Yea, screw me. Long, grumpy day yesterday. Sorry. Although your spirited response did make me laugh!!

We all started at the beginning, not knowing which end of the wrench to use. Put it this way, the first repair I ever needed and paid for was while in college and very poor. The mechanic told me my driveshaft was bad and I forked up $150.00 in 1978 for a new one. To this day, I'm convinced that I most likley only had a bolt or two loose on the thing. Live and learn.

Good luck--Paul
Paul Hanley

This thread was discussed between 10/12/2003 and 11/12/2003

MG MGB Technical index

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