V8 oil pressure figures

devilsplaymate

devilsplaymate

Member
Does anyone out there know what healthy oil pressures a v8 should be running hot & cold?
I hear these engines pressures are not renowned for being that high. I get 35 - 50 psi cold & 15 - 30psi hot (idle - 3000 rpm)
Thanks
Glen. :twisted:
 
I get the same figures as you do, people claim to get 50psi at tickover so I thought mine is a bit low too :?: .
 
Thank you for that. The engine runs very well with no knocks or bangs, even after standing after a hot blaze down the country lanes!!
 
The handbook states 'under normal running conditions the oil pressure indicator needle should register 30-40psi. The needle may drop below this when the engine is running at idling speeds but provided it returns to approximately 30psi immediately the engine is speeded up, the oil pressure can be considered satisfactory.'

So yours is correct. What is more important rather than the absolute number though is that the oil pressure should remain stable at a constant engine speed.
 
Back when I had a V8 (getting another one soon 8) ) I was concerned with the very low oil pressure.

So after a little homework I discoverd that the oil pump on the P6 V8 was considered marginal when new, and after a few years of running it was further considered to be inadequate. This starved the rocker shafts and many other engine parts of oil.

I bought a high pressure, high volume oil pump from Real Steel, and also a new set of big end and main bearings.

It took a while and I got very messy, but I managed to change the shells with the engine in situ, and changed the oil pump (Had to take the front cover off for that :shock: ). Not sure how sensible it is to change the big ends and mains in situ (take some advice before doing this), but then I were just a lad in those days and never did conform to the norm.

At tickover cold it produced around 45psi which dropped to around 35psi when hot.

It apparently increased the volume and not just the pressure.

Result, the engine did feel freer, didn't tappet rattle when cold after a while parked up, and didn't overheat so easily if it spotted a traffic jam.
 
quattro said:
It took a while and I got very messy, but I managed to change the shells with the engine in situ, and changed the oil pump (Had to take the front cover off for that :shock: ). Not sure how sensible it is to change the big ends and mains in situ (take some advice before doing this), but then I were just a lad in those days and never did conform to the norm.
Click to expand...

I've done loads in-situ, and with care they are no problem, however I have known people wreck engines trying. New shells also help stop the rope seal rear mains leaking.
 
Thanks for the helpful information.
Just a quick mention about changing the big end bearings - reasonably easy to do in situ, drop exhaust downpipes & support on axle stand, remove sump (you may have to turn engine a little for the sump front end to clear no.1 & 2 crank web). Replace one set at a time, taking care not to get the bearings the wrong way round (ensure the bearing tang engages with the cut-out in the con rod/cap). Use plenty of oil & ensure everything is clinically clean. Torque as per workshop manual. Then reassemble. Treat engine gently for the first few miles & keep an eye on the oil pressure.
My oil pressure improved by about 10psi (shells were worn down to the backing - crank ok).
:wink:
 
DaveHerns said:
Harvey

What goes wrong fitting shells in situ ?

I was going to try this

Dave
Click to expand...

Big ends are easy, (as described in the previous post,) but it's a waste of time doing just those, you need to do the mains as well. For this you should slacken the fanbelt to allow the front of the crank to drop as much as poss, then remove all the mains caps and fit the correct shells to those. Then the upper shells have to be slid around the crank (after sliding out the old ones) into position ensuring the tang engages in its recess. The front one is a pain because it's above the crossmember, and the centre one has the thrusts which is a bit more difficult, the rest are more easy. Refit the caps in the correct order (and the right way around) and away you go!
Wherever possible (which is all the big-end shells, and the mains in the caps) I coat the bearing faces with "Graphogen" You can get some on the upper mains, but as you slide them round most of it stays on the crank.
 
I did the main bearings one at a time as I didn't want to put any pressure on anything down there, especially the rear oil seal.

When you tap the mains out i.e. tap them gently from the end opposite the location tang (is that what it's called?), ensure that you don't scratch the crankshaft surface as this could cause a hot spot and wear the new bearings very quickly. Just be very carful with any wearing surfaces and screwdrivers!

Make sure that the new bearings are the same size as the ones you are replacing too. When you remove them they should say +.010 or whatever. If the bearings are plus ten thou, then make sure you replace them with plus ten thou.

Removing all of the bearing caps could allow the oil to drain out of the crank and leave the oil pump dry, so best to take the spark plugs out and spin the motor over before starting it, to get some oil pressure.
 
quattro said:
Removing all of the bearing caps could allow the oil to drain out of the crank and leave the oil pump dry, so best to take the spark plugs out and spin the motor over before starting it, to get some oil pressure.
Click to expand...

Whether you remove the caps one at a time or all together wont make any difference to how the oil drains out, and the oil pump won't drain unless you remove the filter, but doing one at a time will make knocking the shells around a lot more difficult. Spinning it over to get some oil pressure makes good sense either way, although using "Graphogen" would allow it to run for a good while without any oil there at all.
 
You must log in or register to reply here.
Back
Top