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deroiste
deroiste

Posted: Mon May 26, 2008 1:49pm

Post Subject: BMC 2.2 Oil Pressure

When I use my boat with a 2.2 BMC engine installed the oil pressure goes up to 50 lbs/sq.in. It holds this pressure for about an hour at 1500 revs. After this period of time the pressure slowly drops to about 30 lbs./sq.in. and holds steady, still at 1500 revs. However when I drop the revs for berthing, maneuvering or when ticking over the oil pressure drops to about 12.5 lbs./sq/in and the pressure warning light flashes and the beeper beeps. I replaced the oil pressure sender with a new one but the results were the same. Do I have a problem? If so what do you think the cause of my problem is? Am I doing damage by running the engine at 12.5 lbs./sq/in.? The engine runs smoothly at a water temperature of 75 degrees celsius. Thanking you in anticipation, Sincerely Conchubhar.

Tony-B
Tony-B

Posted: Mon May 26, 2008 5:55pm

Post Subject: BMC 2.2 Oil Pressure

Dear Conchubhar I no longer have a BMC 2.2 manual, but its later development the 2.5 manual gives a hot oil pressure at 1500 rpm as 50 psi and at idle (hot) of 15 psi.So I do not think your figures are that far out. However I would have expected a little more that 12 psi on idle. My first thoughts are that the oil pressure warning lamp sender unit is faulty. This will have one or two wires attached to in and mounted fairly low down on the engine block on the right hand side. As far as I know the easiest way to test it is by substitution (fit a new one). A long time ago I had very similar symptoms on a BMC B series petrol engine (a very similar design) and that turned out to be the oil pressure relief valve stuck open. As this can be checked at no cost it might be a good first check. The valve and spring can be found under a large domed hexagon plug, perhaps a inch or more across the flats again mounted fairly low down on the right hand side of the engine. Remove the spring and put a length of suitably shaped wooden dowel into the valve to pull it out. The clean everything up and still using the dowel ensure the valve makes easy contact with the valve seat. The free length of the spring on the 2.5 is given as 3 inches. Please double check this figure in the 2.2 manual before trying to stretch the spring back to free length. NOTE TO OTHER BOATERS - Never stretch or pack oil pressure relief valve springs in an attempt to cure low oil pressure - it is rarely the valve at fault. Finally what oil are you using? If it is not an SAE 20W50 then change to that. The engine must be all of 30 years old and was never designed for the modern "thin" oils. Commal make a good 20W50 in API CC which should be available for most motor factors. A Unipart 20W50 will also be fine. Please let us all know how you get on Tony Brooks

deroiste
deroiste

Posted: Tue May 27, 2008 9:51am

Post Subject: BMC 2.2 Oil Pressure

Dear Tony-B, Thank you most sincerely for your prompt reply and advice.I'm glad you feel that it is not a major problem. I will follow your instructions at the earliest opportunity and will let you know how I get on. Regards, Conchubhar.

deroiste
deroiste

Posted: Wed Jun 11, 2008 10:18am

Post Subject: BMC 2.2 Oil Pressure

Dear Tony-B, I followed your advice and took step one i.e. changed the oil for a SAE 20w50. This seems to have done the trick. Kindest regards, Conchubhar.

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