Lagondaforum

Subject: Oil pressure fluctuating...

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Having got my engine running quite nicely, I find that the oil pressure at startup usually goes straight to maximum. After a few minutes, as the oil thins, it falls back - maybe to 60 psi or so. Then it may suddenly drop to the correct, limited value of approx 30 psi from which it occasionally flicks up again to a very high value which may be maintained briefly or for some time.

It's not the gauge - I substituted another.

To me, it has to be the relief valve sticking for some reason. But I've taken the plunger out and it doesn't seem damaged or excessively worn. Has anyone else seen this? And if it is the valve, does anyone re-condition oil pumps?

Thanks,

John

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Subject: Re: Oil pressure fluctuating...

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All I can say is that I had exactly the same problem - oil pressure going from the end of the scale to a nice 30 psi, then going up again and eventually ending up at a nice 20 psi. I never found out why. My advice: don't worry and leave it like that

Subject: Re: Oil pressure fluctuating...

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Thanks Oakley, that's advice I'm happy to take. It would be nice to know what's happening though.

John

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Subject: Re: Oil pressure fluctuating...

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Hi John,
I have the same symptoms from time to time and agree with Oakley. having checked things over it usually manages to hold 30 - 40 when hot. Sometimes it decides to read 20 which introduces heart flutter but next time 30+ again. Very curious. I hope we don't all suddenly have a painful find out why.
don

Subject: Re: Oil pressure fluctuating...

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Dear John & Don,

I have had a similar problem. On my original engine, without modern oil filter, the pressure would go up to 45, and cut off, then settle to 25-35 when hot (down to 20 when very hot). The bearings are all OK and the engine has done about 60k miles since last rebuilt. I have put another rebuilt engine in the car with a full flow filter, this goes off the dial when cold despite fitting a weaker relief valve spring, then settles down to 25-35 when hot. I also had to fit a non-return valve as the oil would not pick up (even after priming the pump). I never had this trouble with the original engine. Maybe the pressure has something to do with the filter, although I'm not sure what. The filter has to be done up really tight, otherwise the seal leaks slightly. The engine now in the car has shell bearings whereas the original's are metalled. Doen't help you, but you're not alone! Lets hope we are not building up trouble. Kind regards, Roger

Subject: Re: Oil pressure fluctuating...

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Dear Don and Roger - many thanks for the inputs. It's nice to know that I'm not alone with my misbehaving engine. Oddly enough, I've never seen the effect with my 14/60 which is essentially identical. Cars, I hate them.

John

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Subject: Re: Oil pressure fluctuating...

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You could ask Alun Jones (Wessex Workshop) to refurbish your oil pump. He is very good at that and might be able to persuade it to behave more sensibly!

Subject: Re: Oil pressure fluctuating...

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Alan Brown has a recommendation for 2-Litres with low or fluctuating Oil Pressure.

1. Cut a 2 inch square of adhesive Duct Tape.

2. Clean glass on Oil Pressure Gauge.

3. Stick Duct Tape over Oil Pressure Gauge.

The recommendation has served Alan right for over 40 years, so I suppose it's worth considering !

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Subject: Re: Oil pressure fluctuating...

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A long time since we had correspondence on this topic.
One of my oil pumps primes reasonably well. The other doesn't, yet it performs very well on the bench, when connected to a source of oil. Indeed it empties the container in no time, so it shifts a lot of oil.

I gave up with the non-return valve because it caused more problems.
The pressure relief valve merely recirculates the oil in the pump, it does not discharge the excess oil into the sump. It relies on the large pipe from the sump being unrestricted so the pump effectively 'marks time' at the correct pressure. The non return valve allows the pump to keep drawing oil at maximum volume so the pressure builds up and up in the pipes. My gauge was reading 100psi, with oil coming out of the top of the pump, even though the cap was screwed down tight, with a good fibre washer in place. When I removed the non return valve everything went back to normal, max 40psi and a constant 30-35psi when hot.

I know others haven't had this problem, so perhaps they modified the non return valve in some way or introduced a way for the relief valve to vent into the sump. Or maybe their oil pumps don't ever produce high pressure because they're worn.

Subject: Re: Oil pressure fluctuating...

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WOW 100 psi is very very high - I recall the old saying if the pressure needle moves thats good [really?] but generally 20-25 is fine...
Never had fluctuations in needle readings but is this caused by filter in sump being clogged and then swirl in oil adding that effect in?...
My issue is how to keep the engine oil tight externally...

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