MGB idle oil pressure too high?

The way the oil pump works, it pushes oil at the galleries to force it up to where it's needed. If there isn't enough restriction, e.g. all the bearings are slack, etc, the oil gushes out and the pump can't keep the pressure up, which means the more remote parts needing lubrication won't really get enough oil.

So when the engine is running at a decent speed, a low oil pressure is a worrying sign, depending on the engine and throughput, obviously. If the oil pump is worn, it won't pump enough oil to meet the demand and bring the pressure up. At idle, it pumps slower and a low oil pressure is not surprising, then the various bits don't need too much oil pressure either, at idle.

The pressure should never go above a certain level. This is because the pressure relief valve dumps oil back into the sump so that the pressure never goes higher than that. To exceed the high oil pressure means you have a faulty relief valve. This can also drop your oil pressure to a lower maxium point if it opens up at too low a pressure.

For the pump to read high all the time, something is wrong. The obvious thing is oil isn't going anywhere. The pump pushes it up to pressure and the extra oil is then just being pumped back into the sump via the relief valve, but nothing is being lubricated. Optionally, some of the ways the oil ought to be escaping, i.e. where it should be lubricating things, aren't letting the oil through so pressure is building up even at tickover when the pump isn't working at all hard. Then there could be a gauge fault, but I wouldn't rely on that for a moment.

You would expect higher pressure if you have renewed the bearings and things, because they seal better and let less oil through, but you wouldn't expect maximum at tickover.

Thanks, you've got my attention. I took the rocker cover off and started it up, and there is good flow and return there so I know that oil is at least pumping and making it up there. I'm not sure how to check if oil is making it anywhere else. All I changed was the head, oil, and filter so I'm not sure how I could have mucked up anything in the block unless some debris clogged a hole. Maybe I should drain the oil and look for bits, this time flushing the cooler as I recently saw recommended somewhere.

To clarify the behavior, the pressure climbs quickly to 60 or 70 and only dips to 55 or so when idling. When I kill the engine the pressure takes 3 or 4 seconds to drop to nothing. It has been driving fine for the 80 or so miles since the head swap. Would I know about a starved crank by now?

I am sure I have read in one of the MG mags that this problem could be to do with the oil filter itself, especially if everything was fine before.

Check and see if the oil pressure relief valve is not sticking - if its free then would suggest either placing another washer under it or renewing the spring and valve cap. Check the length of the spring.

What's important here is to find out if it''s oiling the rocker arms and valves. Take off the valve cover and see if oil is squirtin from the ports in the tops of the rocker arms when the engine is running. The oil should should flow into the rocker shaft and be thrown through ports in the rockers, then drip from the rocker arms onto the valve stems and pool on the valves and top of the head, such that it overflows into the drain-back holes and thence back to the oil pan. Now, this is at idle. If you rev the engine up, it should throw oil all over the engine compartment because the oil is squirting from the ports in the rocker arms at higher pressure.

If this isn't happening, I suspect that there's no flow into the rocker shaft because the oil passage isn't open all the way from the block to the rocker shaft. This would mean that the main, cam and rod bearings are getting oil flow but not the rocker assembly and valves. Did the hole in the block and head gasket line up with the passage in the head?

BTW, I have a '69 B that has 70 psi at cold idle, 50 at hot idle and

Cheers,

CR dave d wrote:

After taking off the valve cover do make sure you have a rag handy to wipe 3 gallons of oil off your face...

;-))

Mart

In message , Charles & Peggy Robinson writes