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MG MGB Technical - Fantastically low oil pressure

I bought a '73 GT about a month a go for not a lot of money. The shell is very solid. The engine runs really well, and basically it's all pretty good.

Except it's got ridiculously low oil pressure, warm on idle got down to an all time low of 5 yesterday. Once running it seems to pick up to an ok level, but still not great.

Apart from changing the oil and filter, which hopefully will just sort everything out (ha ha) what else am I really looking to do here work wise? The bearings?

I've also got this curious little knock I can loudest at the front end of the engine, it sounds like a ringing bell that keeps getting hit again.

Cheers for any advice,
Greg
Greg

The ringing bell could be the grommets on the cooling fan bolts perished. The bolts clamp spacers to the water pump, and the fan 'floats' on the grommets. make sure you have those spacers, a fitting kit should include grommets, spacers and lock-tabs. The bolts should have plain shanks which are a snug fit where they go through the spacers.

Hot idle should be 10 to 25psi, and running 50 to 80, but the lower of those figures is an absolute minimum and most people get the higher figures, or better in the case of idle. First thing with oil pressure issues is always try another gauge. If that gives very similar or the same results then it looks like oil pump or more likely bearing issues. Changing the oil and filter is unlikely to do anything to the pressure (unless the oil has the consistency of water), a blocked oil filter is likely to result in a higher than normal oil pressure whilst simultaneously reducing the flow of oil to the bearings, even where there is a relief valve.
Paul Hunt

Where would I be able to get a fitting kit? If those grommets had perished, would there be free play on the fan?

The thing with the oil is that I don't actually know what it's got in there. Or how long it's been there. I do know it sat and didn't move at all for at least 10 months.

Looks like I need to borrow a gauge off some one, then. I'm prepared to do the bearings, it's a near 130k engine, I have no idea if they've ever been changed.
Greg

Weak spring or worn surfaces in the oil pressure relief valve can also cause low oil pressure.
J Heisenfeldt

A fitting kit should be available from any of the usual MG parts suppliers.

You certainly need to change the oil and filter if they are unknown quantities, some very cheap oils do have the consistency of water when they are hot.

The workshop manuals recommend changing the big end and main bearing shells every 30k to 50k to get the longest life out of the crankshaft. That might be a bit excessive for road i.e. non-competition use, but 130k if it hasn't been touched would be a very high mileage. The shells have a soft white-metal coating which is designed to wear without damaging the crankshaft surfaces. That is on copper, which is a bit harder on the crankshaft, but is useful as if any of the shells show signs of copper then they should be changed. If you go through the copper as well not only do the clearances get bigger and hence the oil pressure lower, the risk of hammering between crank and bearings increases, and both of those plus the harder material under the copper all contribute to crank wear.
Paul Hunt

Start off any car's new ownership with an oil and filter change to the right types and quantities. Oil use Castrol GTX 20W 50 for something thats on the factory recommended list. Get a filter with an anti drainback valve, then with fresh oil, the right amount and type, then see what you have for oil pressures, if still low then you probably have a problem.
Wayne Hardy

Greg, all good advice. One thing we tend to overlook is the possibility of a gauge that's out of calibration. Before starting any major engine work I'd get another gauge and hook it up. You should be able to get an aftermarket gauge for under 20 quid for a temporary installation that will at least tell you if your original gauge is close.
Bill Young

This thread was discussed between 20/08/2008 and 22/08/2008

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