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MG MGB Technical - Oil pressure going mad at startup

Hi,

Took the B this morning to bring my sister to school, and once more (it's really not the first time, I'm affraid) the oil pressure went berzerk:
when I start the engine, the pressure rises to +- 40, then it drops to 20 then to ZERO! After that, it rises again to 40, then 20, then 0. And this is repeated for a number of times! Tomorrow it lasted for about 5 full minutes.
The car is a 1965, 5 bearing 18GB engine, completely stock except for a Peter Burgess fast road cyl. head (as far as I know of no other mods had been made before). It has been in storage from the end of november until the end of february and it has been acting strange ever since...
The gauge is, as far as I know of, a mechanical one, so I guess it's not the gauge going mad.
What could be the cause of this and how can I solve it??? (is it perhaps the oil pump that's having probs with the cold nights over here, as it's still freezing at night)

Regards and thanks in advance!

Alexander
Alexander M

Sometimes I have noticed that when the engine is very cold, the oil pressure is lower than normal because (I think) the viscosity is too high to get through the capillary tube feeding the gauge. After a few minutes of warmup, the pressure indicated actually rises instead of falling, and then once the engine is up to operating temp, the pressure falls slightly as one would expect.

I would say that if your oil pressure acts normally when the engine is warmed up that you're probably OK, and not to worry. Does it sound like your head is starved for oil, with excessive clacking, on startup? If not, again, I wouldn't fret too much.
Paul K

Just a thought:

Perhaps air has gotten into the capillary tube, (from sitting for a long time), or drained back.

Open the nut on the back of the gauge until oil appears.
glg gimbut

Either that above or temporarily fit an electrical unit in place of the standard cappillary tube. That will eliminate problems with a faulty gauge.

Martin
Martin

Alexander,

May be a slight possibility that the "overpressure" valve is sticking also. This is in the left side of the block. Possibly, when the oil is cold and thick the valve opens, and that could account for the loss of pressure.
Cheers, Doug
Doug Keene

While we are on the subject of fluctuating oil pressure, I would be curious if anyone else's B does what mine does. Mine fluctuates up and down almost all the time - like the relief is popping open and closed.

It's done this for about 25 years and did after a rebuild during which I replace the relief valve spring.

Just curious.
Richard Smith

About 60% of the time my oil pressure will be normal around 55lbs. Then it will drop to 0, then go back up. It started about 3k miles ago and has gotten slightly better after my oil was just changed.

Sort of thinking that it is the oil pump, but not liking that idea at all since I just read that you need to lift the engine to replace it.

Cheers!
-Jason
1970 mgb roadster
Jason C.

Just to rule it out, I would change the oil filter.

There was a great article floating around a while back, Bob used to have a link to it on his web site.

It listed the variety of oil filters, the different manufactures (while there are many brands there seem to be only 3 or 4 places that actually make them), and some of the problems that they can cause when they fail.

I searched the archives, and the search for the title
"oil filter study" found it, but the link is no longer good.

Maybe someone has a more up to date link.

Craig Amos

Hi Richard...

My oil pressure fluctuates ( actually flickers is a better word, over a pressure range of about five lbs )but only when its hot...and it's also done it for about 25 years!!

Cheers
Mike
mike donaldson

Thanks for the feedback, Mike. Guess it just must be the nature of the beast...

Richard Smith

I found that oil filter link on another site if anyone is intrested.

[url=http://www.frankhunt.com/FRANK/corvette/articles/oilfilterstudy/oilfilters.html]http://www.frankhunt.com/FRANK/corvette/articles/oilfilterstudy/oilfilters.html[/url]
C Amos

Try this one'

http://minimopar.net/oilfilterstudy.html

It is by a mopar guy, but useful info.

It has floated around here for years
Craig Amos

This thread was discussed between 19/03/2003 and 25/03/2003

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