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MG MGB Technical - Oil Pressure problem

I have just fitted an oil thermostat (mocal push on type} to my 1980 MGB and the oil pressure has nose dived.
The car was running normally a few days ago with normal oil pressure rising rapidly to around 60 psi after start and never going below 25 psi when hot idling.
I cut into the cooler hoses just behind the expansion tank and took great care to ensure it was plumbed in correctly. I did not prime the pipes with any oil. Correct me if I am wrong, the pipe from the engine comes from the rear of the block, and to the engine via the filter. After checking the oil level I started up from cold and was concerned to see the oil pressure rise slowly to around 35psi. I let the engine get to temp and the pressure fell back to 25psi. The cooler hoses to and from the thermostat, and the stat itself, got hot. Those to and from the cooler remained cool.
When I blipped the throttle, the pressure actually dropped each time by about 10psi. Once it got warm enough for the cooling fan to cut in the pressure started slowly falling away and I shut the engine down. The engine sounded normal throughout with with no knocking or unusual symptoms.
I let it cool for 10 mins an started again. The identical thing happened again after an initial reading of 35-40 psi.
I have no reason to believe that the guage is suddenly reading incorrectly, so assuming it's OK has anyone got any ideas??
Phil Barton
Philip Barton

Hi Phil. I would be inclined to diconnect the oil stat and just join the pipes to and from the engine together. If the pressure is still not correct you have an engine or guage problem but if it is now good the stat or connections are probaly at fault . Jim
j soutar

Phil,

I'm not familiar with the type of oil thermostat you mention but wonder, is it possible you have obstructed the oil flow by inserting a sensor into the hose? Alternatively, done that and/or/also provided an alternative flow path for the oil which has it 'looping' in some way which inhibits its return path through the filter?

Regards
Roger
Roger T

The thermo is in the Moss catalogue and can be seen online. At a low temp the oil is diverted away from the cooler and straight to the inbound hose to the filter. Above 80c the oil takes its normal path to the cooler.
Would a blockage in the stat or in the filter create these symptoms?
Phil
ph barton

Phil,

i have installed the same item on my V8 and on the roadster and there was no dropp in pressure readings on bothe the cars. The thermostates came from Moss.

Might be there is something wrong with the finish of the valve body of the thermostate. I would take it out and connect the lines directly. If the readings return to normal then, have an excahnge thermostate, otherwise check the oil pipes, as they are made of an inner and outer hose that might come apart from each other, partly blocking the inner diam and reducing flow capacity. The oil pipes should be renewed in intervals and a good source for cheap and high quality oenes are most hydraulic service garages that have better (commercial) qualities than sold by some very well known MG parts 'Specialists'.

Ralph
Ralph

Think Ralph may be correct. I would call Moss. May be the valve is not closing fully and it is actually impeding the flow.
BEC Cunha

Thanks guys, I will bypass the stat next weekend and see if there is any difference.
I cut the hoses slowly with a hacksaw blade. I didn't notice any debris getting into the hose, but I will also replace the filter at the same time.I'll keep you posted on the result.
ph barton

This thread was discussed between 03/11/2007 and 05/11/2007

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