sq 4 oil pressure....

[john.bebb]

Hi folks, 'fraid to say I'm quite perplexed at the reverence & respect many people give to an uncalibrated indicator...

[bob cottam]

Come again John.....????

[camstevens]

I use Penrite 25W/70 in my Mk1. 75 psi cold, independent of engine speed; 55 psi hot running; 25 psi hot idle.

Hi Simon
25w70 does sound like a prudent option. Did you run this grade when the engine was newly rebuilt? Would a higher viscosity at running temp help or hinder running in?

Cam

[simon.holyfield]

I actually ran a very cheap 20w50 during running in. Then I switched to the Penrite Heavy after 500 miles, then to Penrite Medium at 1500 miles, then to a 20w50 at 2000. That's what I'm currently using (note that this thread is quite old now).

I think if I had my time again I'd run on a running in oil, and then go to a 20w50.

Alongside these oil changes there is a lot of familiarisation, and fault finding in the lubrication system around the relief valve and the oil lines, so I would be very wary of following my path!

[john.bebb]

Hi folks...

(Bob) "Come again John.....????"

- merely to emphasize that I wouldn't trust any oil pressure gauge to give an accurate value in psi or whatever... (unless it has a valid NPL certificate)... observe it solely as an uncalibrated analogue meter (i.e. more is more & less is less)...
Best indicator is your eyes down into the oil tank when the cap is removed, having first checked it ain't being spewed down the road!

Cheers, John.

[bob cottam]

Hi John, re the gauges, ever cautious, I did wonder about this.
I decided in the interests of Science and Advancement to do some field (workshop) research here to find out just how good or bad is the accuracy of the various small pressure gauges I have available.

I tested seven gauges with foot pump air on a common manifold, the readings of all seven varied by 5psi in total between 0-65psi.Not too bad..

Worst offenders were a pair Smiths 2" dashboard jobs with that 5psi difference, followed by two identical, new, glycerin filled ebay jobs reading 3-4 psi different out of the box, and (best?)two identical 40mm ebay cheapies which gave identical readings throughout, bless `em. Number 7 was an old ebay cheapie 160psi job from under the bench which came within the 5psi range I found.
With no calibrated datum to work from, I made the decision that a good guesstimate of true pressure was somewhere within the 5psi range found, and I was happy to use the two 40mm gauges to test my engine pressure, and compare readings at either end of the rocker line.

So what do we learn from this... well obviously I need to get out more....( well we are under (increasing) Lockdown!). I think the engine oil pressure indicated will be reasonably near to the truth, and with an indicated 65psi on cold start (bearing in mind the Morgo pump blows off at 55psi) i feel re-assured that my squares bottom end rebuild is up to snuff.. I suppose the really useful information here is that the pressure drop along the rocker feed line is SO significant (with an unrestricted cam oiler kit fitted). At any one time the running pressure at the crankcase take off is approx double that of the far end of the rocker feed... Bob.