Stag v8 low oil pressure

[ddstr6]

Hello,

I am a new member to the SOC and hopefully fellow members will have some insight as to what the cause of my car's low oil pressure is. The original v8 has been rebuilt, new pistons, bearings, rods, valves, oil pump etc,etc. Tolerances all checked while assembling and within spec. ( did not check the jack shaft!)
Engine has good oil pressure at start up but as it warms up the pressure drops. When the engine is warm and at idle the oil pressure is 10-15 psi. While driving( warmed up) pressure is in the 30-50psi range.

Any advice is much appreciated.

Dave Q

[jleyton]

Hi Dave,

Welcome to the forum.

Lots of us suffer from Stag paranoia but with those figures I wouldn't be panicking. 10 - 15 at hot tickover is not disastrous however if the engine has only just been rebuilt I agree that you would expect somewhat higher.

One of the first things I would check though is the accuracy of the gauge that you're checking the pressure with to ensure that the figures are correct.

When the cars were almost new it was not unknown for the oil pressure light to flicker (Ie around 5 psi) at hot tickover after a hard run

Cheers

Julian.

[ddstr6]

Thanks Julian,

I will check the guage. Hopefully it is " off ".

Regards

Dave

[flying farmer]

Pressure at tickover also depends on idle revs, and I assume you are using a good quality 20/50 oil and not something thinner. If you have full pressure by 2000 rpm it suggests there is no problem at all, if it takes a lot of revs then there is a problem somewhere, but probably not worth stripping the engine unless you see it deteriorating
Neil

[staginhiding]

The modern thinner oils definately can cause a problem,make sure you have a good 20/50 in there..

[martin]

Hiya, I agree with Julian, not too bad, but ought to be higher on a "new" engine. Another possibility is the oil pump relief valve spring, try swapping it for the original, minimal disruption and free. Martin.

[V Mad]

If none of the above are the cause, it could be cam bearings as they are not replaceable. They would probably rattle a bit though.

[davidf]

In my experience, low tickover pressure can be caused on a good engine by the poor design of the spring in the relief valve of the oil pump. I used to work for a manufacturer of very sophisiticated valves, and when I showed this spring to our design office, and explained what it was supposed to do, they all fell about laughing. Analysis showed that the valve cracks open below 20 psi, so with low delivery from the pump (at tickover), you aren't going to get any more pressure. Some of the oil is already recirculating to the pump inlet.
They very kindly specced up a spring that holds the valve from cracking till about 50 psi, and gives full flow at 65 psi (about where the standard spring give full flow). I had a batch made up (this was back in the late 80's), and I have run one ever since. Tony Hart checked it out to give me some feedback - he was concerned about high pressures he recorded under test, but he was looking at very high engine revs. So, if you are racing your Stag, perhaps we wouldn't recommend this oil pressure boost. I did used to sell on the spare springs I had, and everyone who had one liked the results.
I don't have any more spare springs, and I don't have any connections with any spring manufacturers any more, but I do still have the spec of the spring.
If you are interested, I could send you a copy of the spec., and you might get one made up locally.

[ddstr6]

Thank you all!
I feel a little better about the oil pressure now, I am not keen to tear down the engine. I have been running a very good quality 20/50 oil ( Castrol ) and an oil stabiliser. The pressure comes up as soon as the revs are increased.
Perhaps I will "cure" the issue by removing the oil pressure gauge and put the clock back in!
Thanks again everyone

Dave Q

[Bob Heritage]

I think a lot of us have similar pressures as you, the original spec of the pump is only about 40lbs anyway. Aftermarket pumps are higher, some say too high. Good oil is a must, I used to use Castrol (now owned by BP) but lately found that is lost it's viscosity quite quickly, I now use Valvoline VR1 which is highly recommended amongst a lot here on the forum.

[martin]

I think a lot of us have similar pressures as you, the original spec of the pump is only about 40lbs anyway. Aftermarket pumps are higher, some say too high. Good oil is a must, I used to use Castrol (now owned by BP) but lately found that is lost it's viscosity quite quickly, I now use Valvoline VR1 which is highly recommended amongst a lot here on the forum.

HERE HERE ! Martin.