low oil pressure query

[jesfirth]

just fitted new big end bearings and a john eales baffled sump and oil pick up. engine fired on the button - oil pressure 60 psi when cold (fractionally higher than before) BUT once hot at idle it drops to sub 5 psi with the occasional flash of the orange warning light (which means that both mechanical and electric guages are working as they should) - touch the throttle and the pressure picks up just fine to 15-20 psi at 2000 rpm.

I have put in 10 40 semi synthetic and 400ml of ZX1 so perhaps a fraction thin but not enough to cause this.

the engine is not overheating although it does seem very hot in the engine bay (could be my imagination though) and the fans are cutting in and out correctly.

What have I done wrong? or could it be a coincidence (dont believe in those) such as oil pressure relief spring or oil pump - any ideas welcome?

[jasoncook]

Hi did you remove the oil pick up this can be a symptom if the gasket splits or its loose,drags a bit of air in at low pressure. Have you had a micrometer on the shells though i expect it would knocked like mad at start up if they were undersized.

[jesfirth]

gents it worked fine at first - ok when sat at idle on the drive - the shells are standard size (matching those that came out) and no knocks at all - i drove it 5 miles before the pressure dropped when it got hot.

haven't touched the oil pump but it is a new john eales oil pick up to match the sump, but fitted with the requisite gasket. also a new oil filter

i have just been back through everything i have done.

just putting the torque wrench away and realised it was set on Nm not Lb feet for the big ends! so i have torqued them to 52 lbft instead of 35lb ft. Oh balls. could this be the cause and will this actually make any difference in the real world or should i free them back off to 35lbft?

[Barkychoc]

I would be pulling the oil pump apart - checking the pump base for wear and that the oil pressure relief valve isn't sticking (thats if you can get the bloody thing out, it can be a bugger!)
The pump gears and relief valve cost sod all anyway so chuck them in the bin and fit new. If the oil pump base isn't too bad you may be able to reface it rubbing it on a sheet of wet and dry on a piece of glass.
Personally I'd leave the torque settings alone now its all together.
I am still running in using Unipart 20/50 but its at 25psi hot idle and I've done several hundred miles now (pre serp 3.9)

[griffdude]

I use Silkolene (Fuchs) ProS 15/50 in my pre-serp (only a little 4.5) with a JE baffled sump & get 25+psi hot idle. With an oil cooler.

[TVR Beaver]

Quinny said:

Barkychoc said:

I would be pulling the oil pump apart -

But he hasn't touched the oil pump, and the pressure was fine before....

Personally I wouldn't start pulling something apart that was fine before... It'll just add another variable into the mix...


Concentrate on the things that have been changed.... Bearings, and pickup pipe....

+1

[spend]

Thats the classic outcome when st oil gets overheated IMHO, try some decent oil before you worry.

[dmjw01]

jesfirth said:

just putting the torque wrench away and realised it was set on Nm not Lb feet for the big ends! so i have torqued them to 52 lbft instead of 35lb ft

Perhaps I'm misunderstanding, but surely if your torque wrench was set to Nm when you intended lb.ft, and you set it to "35" intending 35 lb.ft, you had actually set the wrench to 35 Nm, which is about 26 lb.ft. In other words, haven't you under-torqued rather than over-torqued?

__
David

[dumbfunk]

^^ We may have a winner??

[jesfirth]

no definitely 52 lbft on the torque wrench setting so it is 14lb too high on the big ends sorry for confusion.

thanks for all the input.

i think i will try different oil and filter first and then if that doesnt work refit the old sump and pick up and see what happens with that.

fingers crossed

[big geoff]

I would get a known oil pressure gauge (garage test tool ) and that would give you a true reading

[tuscanlad 2]

try changing the oil pressure converter first
it made 10 psi difference to mine
The sender
Simon

[haircutmike]

tuscanlad 2 said:

try changing the oil pressure converter first
it made 10 psi difference to mine
The sender
Simon

The oil pressure gauge sender is seperate from the oil pressure light sender and the oil light was flickering so can't be that.

[roysum]

Maybe.....but wouldn't be the first time two components play up together. Relatively inexpensive to at least change the sender before getting to involved. Or perhaps plumb in a mechy guage. Nothing to lose IMO.

R

Edited by roysum on Saturday 1st January 22:07

[haircutmike]

Got my new mechanical oil pressure gauge fitted in the dash.

Reassuring to see decent pressure after yoyoing readings on the lecky gauge
!

[v8 racing]

Just out of interest which bearings did you use (make), most after market bearings allthough are for the rover v8 engine are too wide for the 500 crank, if these are fitted the oil gets trapped between the shells and crank, after a while the oil gets that hot you may as well have water in your engine as the oil isnt doing much good, you want a good 15thou play between the two rods.
Rob

Edited by v8 racing on Monday 3rd January 11:26

[jesfirth]

not sure which shells i used but got them from racing green-to my untutored eye they looked fine. am going to pull the engine out next week for a bottom end rebuild, check the oil pump, pressure relief valve etc. thanks for all the input to date