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MG MGB Technical - Oil Cooler question

MGB GT 1969:
Previous owner removed the oil cooler (leaked?) and am having difficulty getting a new one in Singapore. Hope to get one from UK and installed end Jan.

So running without the oil cooler:
At cold start up: pressure gauge stays at zero for 20 seconds, then goes to 70 @ 3000rpm, pressure idicates 40 at idle.
For first 10 of driving : drops to 50 @3000RPM, and down to 25 at idle

After about 10 miles, pressure drops to 40@3000rpm, and to 10-15 at idle.

Question: will installing the oil cooler fix this and should be checking anything else as well?

And advice?
Thanks

Harp Bamrah

Harp-
Installing an oil cooler shouldn't have much effect on this unless you're using garbage oil. It definitely shouldn't take 20 seconds for your gauge to show oil pressure. You may have a problem with your relief valve or a leakdown problem, or both. What kind of oil filter are you using? What weight oil? The changes in pressure readings are very suspicious. 40 PSI at idle at cold startup, 25PSI at idle when warm, then 10-15 PSI at idle when hot? That's too low! How many miles are on the engine?
Steve S.

Steve
I have been through 3 oil changes in 2 months trying out the oils. A garage put in some at a service, (20/40?) , and I changed to 20/50 and now I am on High performance synth.
Same results each time. Oil filter is new (inverted filter element type).
Engine was rebuilt about 3 yrs ago which means about 25K miles since rebuilt.
No knocking from big ends, engine sounds very good.
What is a leakdown problem? And how is it fixed?
Thks
Harp Bamrah

Harp-
Your oil filter has (or should have) an antileakdown valve in it to prevent the oil in the filter from leaking down. If it doesn't have one, the oil pump will have to fill the filter with oil everytime that you start the engine. This takes time during which the engine will be running without oil pressure and could be an explanation for why you have no oil pressure during the first 20 seconds of running after startup. Until you can replace the filter, crank the engine until you have oil pressure without allowing it to fire. However, the variances in pressure at different operating temperatures is not likely to be caused by a defective oil filter. You may have a problem with your oil pressure relief valve (bad spring?).
Steve S.

This anti-drain back valve in the filter is an ongoing problem - I am currently using the Moss filter and it still drains back as I too have the long agonizing wait for oil pressure - it's common with the inverted filter setup . I switched to 10W40 and that has helped a lot .

-Nate
Nate

Harp,

I think synthetic oil is too thin for MGB engines, i would stick with a good quality 20/50. This may be your problem, although you say you have the same readings for all 3 different oils. I would also try changing the spring in the oil pressure relief valve.

Scott
Scott Ralph

Another thing to consider is that the oil pump may be sucking air due to a crack in the strainer, or a loose strainer/bad gasket, or it could be that a 3-main oil pump gasket that was used or the pump is loose.

I think that the 20 seconds to get oil pressure is the key. Even if the drain-back valve leaks, it shouldn't take 20 seconds to fill the filter.

Wayne
Wayne Pearson

Harp. I removed the oil cooler on my 74 roadster over two years ago. If
anything the oil pressure is a little better with oil cooler removed. With
the oil cooler removed the pump doesn't have to pump oil through the long
lines and the cooler. I have not experienced any problems running without
an oil cooler. However, I'm not suggesting you not run an oil cooler, I'm
just stating my experience without one

I don't know what brand of filters are available in Singapore, but Mann,
Motorcraft FL 300 and Wix seem to work better than some of the other
brands available here. I would normally suggest that you use another oil
pressure gauge to verify the accuracy of your gauge. But the fact it shows
70 psi with cold engine at 3000 rpm indicates your gauge is probably ok.
Your oil pressure is too low with a hot engine and I would think there are
some internal engine problems that will require correcting to restore normal
oil pressure. My 74 roadster runs at 60+ psi with a hot engine.

Clifton
Clifton Gordon

20 secs is way too long for the pressure to rise. It all depends on your ambient temps, but certainly the oil cooler was fitted to midgets to maintain hot oil pressure. 15W/50 full synthetics are OK but lighter grades are designed for modern engines with tighter tolerances.

I'm looking into viscosities at the moment as I feel that Castrol GTX 15W/40 is more 'rattley' than the 15W/50 was, which I don't seem to be able to get locally any more. I've just tried Duckams Q 15W/50 but that is like treacle and takes an age to show on the gauge (on my V8 which has a 'slow' gauge anyway), much more than GTX 15W/40. One thing I have noticed is that you have to read the containers very carefully these days as you can get a line of cans of the same manufacturer, brand, logo, colouring etc but the viscosities are different. For example, Mobil 1 comes in 0W/30, 0W/40, 5W/30, 10W/30 and 15W/50.
Paul Hunt

Another point about "leak down" - even good filters with a one way valve may leak down if the standing pipe in the centre of the filter adapter has been removed by a PO!
Chris Betson

Harp:
My gauge fires up immediately to 75psi but my experience from there on is the same as yours. This happened seemingly overnight. Replaced the pressure relief valve spring, gauge, blew out the flex line and the hard line to the gauge. No change in results. Engine has approx 5000 miles and makes no metal sounds.
Its performance is unchanged in all respects from a year ago except for the change on the gauge. Temperature does not seem to be the problem as it keeps falling as I drive the Interstate eventually ending at 15psi at idle and 45 psi at 3000rpm. If I run it up to 4500 rpm it goes to 70psi but will start to drop. Interested in any changes you make that have an affect. Good luck,
jim mindy

Thanks for all the advise, and comments, and will let you know what happens. Am off the London for a business trip, make a sneak trip to Moss and will come to Singapore back armed with MG parts!

Harp
Harp Bamrah

Mobil recommend 15W/50 full synthetic confirming Paul H's comment.

Following Steve S's recommendations, I'm now trying synthetics and the engine is now almost silent.

Paul
Paul

Chris Betson, can you explain what you mean by "the standing pipe" as I don't think my engine has got such a thing. Should there be a tube sticking up from the filter mount that goes up inside the filter cartridge? If so, what size is it? Can it be sourced or would I have to bodge one?
Mike
Mike Howlett

Mike,

Have a look in the photos page on my website, I have posted a pic of the adapter showing the standpipe.
Chris Betson

Mike,
Sorry, didn't finish answering your Qs

You could cut a piece of pipe to fit - or pick up a secondhand adapter.
Chris Betson

Jim, your experience is worrisome with 15 PSI idle on
a 5000 mile engine. Have you confirmed this reading with
a second gauge? I would suspect the gauge since this
happened suddenly, without onset of any knocking/rumbling
sounds.

If not the gauge,
I wonder if there is a problem with bearing quality -- do you
recall the brand/manufacture of yours? www.aptfast.com has
some info about variable quality of newer bearings.

Harp, I found with my 79 B that adding an oil cooler yielded
an extra 10 PSI at hot idle (went from 40 to 50 PSI on a fresh
engine.) In your
climate, I think a cooler is really needed. The oil
cooler does reduce oil pressure at speed a bit, as noted due to
the length of the lines. But if your engine has a lot of miles,
I would also suspect worn bearings.
Ronald

This thread was discussed between 03/01/2002 and 04/01/2002

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