MGB Oil cooler on '78 MGB

[rtfulk]

I am debating on installing an oil cooler on my MGB. Here is the oil stats: On startup I am at 75psi. At idle 1100rpm I am between 25-30psi. After about 30mins. of traffic driving it drops to around 40psi. If I come to a stop and then accelerate again the pressure will jump back to 50-60psi running through the gears. After reaching driving speed around 2500rpm it drops back to around 40psi.

The engine was rebuilt around 6-7K miles ago and it doesn't use any oil. My question is will installing an oil cooler keep my pressure up to 50-60psi? Any suggestions for or against will be appreciated.

rtfulk

 

[Dave Russell]

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by rtfulk:

The engine was rebuilt around 6-7K miles ago and it doesn't use any oil. My question is will installing an oil cooler keep my pressure up to 50-60psi? Any suggestions for or against will be appreciated.
rtfulk<hr></blockquote>
Your pressures are not too far off from factory specs. With SAE 20-50 oil, the running pressure warm should be around 50 psi minimum at 3000 rpm.

You don't say what viscosity oil you are using.

The viscosity of 20-50 at 210 degrees F should be around 1/3 of what it is at 100 degrees F. So yes, a cooler "might" raise the pressure some. The down side of overcooling the oil is more water, condensation, build up in the oil. It really needs to run fairly hot. If oil temps were approaching 275 & higher a cooler would be good.

The causes of low oil pressure are likely to be, thin oil, low oil pump output due to a plugged screen, or bearing & oil pump wear. I would put fresh 20W-50 oil in & see what the hot pressure is at 3000 rpm.

In view of it apparently running well, & not making any undue noises, I wouldn't worry too much. In any event, an oil cooler is not a good substitute for tight bearings & oil pump in the engine if they are needed.
D

 

[rtfulk]

Thanks for your response. I have just changed the oil and used castrol 20-50. The pressure has always been at the stats I gave even after the rebuild. It may just be a physicological thing with me thinking the pressure should stay around 50-60psi.


rtfulk

 

[Dave Russell]

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by rtfulk:
The pressure has always been at the stats I gave even after the rebuild.
rtfulk<hr></blockquote>
The pressures are kind of low for a fresh rebuild. I was under the impression that the pressure had been higher at one time. Since the pressure goes higher at times, I think you can rule out the pressure regulator & gage but maybe cleaning & replacing the regulator & it's spring would be worth a cheap try. If the pressure gets much lower I would investigate further. Was a new oil pump installed at the rebuild?
D

 

[rtfulk]

Yeah I replaced the regulator and spring last year. I was reading over my post and I did leave out one thing. The other evening it was cool in the 60's and we were driving and the pressure stayed around 50 psi. Sorry for leaving that info out I was so busy giving stats that that slipped my mind. That is why I thought maybe a oil cooler might help. I was told the oil pump was replaced the guy that did it is trustworthy and I wouldn't think he would lie to me.

I was under the impression and I may be wrong...That a true sign of a bad or failing oil pump was when the pressure dropped to 15psi or less at idle speed after the car was warmed up.

rtfulk

[ 04-05-2004: Message edited by: rtfulk ]</p>

 

[Dave Russell]

The oil pumps output, (flow capacity) is proportional to rpm. The flow requirements of an engine in good condition, (leakage through the bearings), should be fairly constant with rpm. So, the pressure should rise a little with rpm & then remain fairly constant as the regulator bypasses more or less oil to maintain it's set pressure. As pump output decreases due to wear, & engine flow increases due to wear, the pump can no longer can keep up with the engine flow requirements & pressure drops, especially at low rpm.

As you say, it would be normal for cooler oil to have higher pressure.

Possibly your engine was built with excessive clearances somewhere in there or the pump is not putting out as much as it should. Causes of low pump output could be, worn pump, leaks between pump & engine, or clogged pump intake screen. A remote possibility would be an air leak on the pump intake side.

It is a tough call. First thing I would do is verify the oil pressure gage with a temporary known good gage. True things could be better but the pressure isn't THAT low. I don't know how inclined you are to pursue the problem.

If you want to go further, pull the pan, Plastigage the rod & main bearings for proper clearances, (.002" max) check the oil pump thoroughly or replace it, & check for pump input or output plumbing leak possibilities. After all of this you may find that it didn't help much. The cam bearings can be a major source of pressure loss & are not easy to check.

I would just drive it until it gets worse or you can't stand to live with it anymore. Put a cooler on it if you wish, at least it will make the gage read higher.

There are folks on this forum who are far more knowledgeable about your engine than I. I'll leave it to them.
D

 

[76MGB]

Hi.
I was thinking about putting an oiler cooler on my 76 B. Can I use any year oiler cooler or are the pre-74.5 different.
Thanks
Quentin