Killer Paranoia Apparatus by William R Blankley

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That's what the letters KPA on the oil pressure gauge signify honest they do. Out of sight, out of mind if your car does not have one. My Bronze Dragon is a compromise, the gauge is calibrated nought to five with no indication as to nought to five what?

Hence I am doubly pleased with the letter from Andrew McAdam, though I will point out that I was rabbitting on about the Manta A, firstly because he has spared the time to give us some feedback, secondly it confirmed my suspicions that the gauge is calibrated in atmospheres.

As to my oil pressure at idle it drops off to one when the engine is very warm, at somewhat over one thousand revs per minute it goes to two and one half, exactly half scale. It used to be two at idle until the trip to the AGM, all this on an engine that has not yet passed 7K since rebuild. What I do know is that the idle oil pressure is very sensitive to the oil pump clearances. The pump cover has been renewed. It is the type with a relief valve, it should have been a plain one but this one was to hand and I was pushed for time so there are two valves in this engine, double trouble! (with two poles the system might tend to instability?) It is perhaps disingenuous to compare oil pressure without making some sort of correction for the oil.

Bronze Dragon is using Mobil 1. I am beginning to form an opinion that Mobil 1 has nearly constant viscosity and that this is very low compared to conventional oil at low to medium engine temperatures. At the sort of temperatures that make 20w50 wilt its still going strong. I shall keep an eye on the situation and report back to you all if, when and what happens.

What is borne in mind is that the CIH engine was designed for 20/50 and it is highly likely that the fixed size holes for lubrication of such things as rockers offer less resistance to the flow of synthetic (5w50) oil so that at idle the pump can only just keep up.

In addition too but not withstanding the foregoing, my friend Rob tells me that the pumps are a weak point and Mr & Mrs Editor point to the pump cover. What’s more if you think that this subject has been flogged to death there is the not-so-small matter of the oil pump gasket, some can be too thick, the GM one is about 0.25mm. The gears are supposed to stick out of the end of the pump by 0.1mm giving a clearance of 0.15mm. As the temperature rises this clearance will increase as the alloy housing must expand more than the steel gears. Since this area affects the idle end of the oil pressure profile it is a good place to check. The actual relief valve itself is singled out for mention in the workshop manual. It dysfunctions, sticking open it dumps the pump output, also the spring wears, since stiffness is proportional to the 4th power of the radius a little wear reduces the spring stiffness dramatically. If the oil filter should become obstructed then the pressure will drop by an amount determined by the by-pass valve. This can be a doomsday scenario.

To my knowledge there have been three types of oil pressure relief valve

1. timing case mounted small ball & spring

2. timing case mounted large ball & spring

3. oil pump mounted (all USA & later GB)

These things are expensive to change in manufacture so this implies that Opel had trouble. We will never know.

By the way, when the engine is at the end of its life Molyslip seems to help a lot. Never use this product in an engine that has not been well and truly run in, not to say run out? There is a Molyslip for gearboxes and rear axles that quiets down noisy gears rather well if they are not too far gone. I have used them on lots of old heaps, impressive.

Always obey the instructions on the can!!!!

William R Blankley

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