V8 Engine Problem

Hi All,

Well its been a while since I have posted a message on here. mainly because my range has been as good as gold..... until now

18 months ago I built a brand new engine for my Range. She is a 4.0 litre non gas..

Last night when I got home from a long run the oil light flickered a few times. This morning she made a hell of a rattle when I started her, but it did clear instantly. The oil light has shown itself again.

I have removed the oil pressure switch and put a oil pressure gauge on the system and run the engine.

The results are not good.......

at 750 rpm (tick over) I have 0 - 8 psi of oil pressure
at 1000 rpm - 21 psi
at 1500 rpm - 35 psi
at 1750 rpm - 40 psi
at 2000 rpm - 45 psi.

These were all taken with a warm engine....

I have checked the obvious and the oil level is spot on.

I have read through the Rave manual and it states the oil pressure should be 29 psi with a cold engine at idle, and 40 psi @ 2400 rpm.

Has anyone had faulty pressure relief valve. My thought was if it was stuck open then the oil pump could not keep up with the demand on a open system. Or am I looking at a oil pump failure!.

When the engine was built. everything was replaced with new.

Any help or thoughts would be appreciated.

Thanks

Bryan

hello mate i think your on the right track , first stop for me would be checking the relief valve , ive come across this a few times over the years not just on rangerovers .
rick.

Hi Rick, thanks for that....

I have removed the cir clip holding the relief valve in. but can not get the blanking plate out the end of the assemble. So have decided to take the front cover off completely, I think I will drop the shells off the crank at the same time just to check for any damage which may have been caused by low oil pressure

Thanks again for your help. I will keep you all posted on what I find.

Bryan

P38 Owner said:

Hi All,

Well its been a while since I have posted a message on here. mainly because my range has been as good as gold..... until now

18 months ago I built a brand new engine for my Range. She is a 4.0 litre non gas..

Last night when I got home from a long run the oil light flickered a few times. This morning she made a hell of a rattle when I started her, but it did clear instantly. The oil light has shown itself again.

I have removed the oil pressure switch and put a oil pressure gauge on the system and run the engine.

The results are not good.......

at 750 rpm (tick over) I have 0 - 8 psi of oil pressure
at 1000 rpm - 21 psi
at 1500 rpm - 35 psi
at 1750 rpm - 40 psi
at 2000 rpm - 45 psi.

These were all taken with a warm engine....

I have checked the obvious and the oil level is spot on.

I have read through the Rave manual and it states the oil pressure should be 29 psi with a cold engine at idle, and 40 psi @ 2400 rpm.

Has anyone had faulty pressure relief valve. My thought was if it was stuck open then the oil pump could not keep up with the demand on a open system. Or am I looking at a oil pump failure!.

When the engine was built. everything was replaced with new.

Any help or thoughts would be appreciated.

Thanks

Bryan

Click to expand...

this is spooky, its an exact replica of what i have although at idle my pressure flutuates less, 3-4 psi (just under oil switch limit) and i had a look at the oil presure relief valve but after removing the clip couldnt get the cap out!!
although recently since curring air leaks around plenum the idle has been stronger and light not flickering on any more, still needs looking at though.

i keep an eye out for your findings.....

Okay,

I have had another day of playing and this is what I found...

I ended up taking the front cover off completley so I could strip it on the bench.

To remove the cap in the end which has a Oring on it. I removed the oil filter and if you look up into the housing you can see the pressure relief valve spring. With a flat bladed screw driver I compressed the spring and out came the cap. ( I then spent 30 mins hunting for the cap as it fired its way out the housing and across the workshop)

This is were it start to get a bit tricky. Looking at the exploded parts drawing on Rave for V8 Disco 2 (as there is not a exploded drawing showing the oil relief valve on P38 or serpentine 3.9 range rover classic) It clearly shows three parts making up the pressure relief valve. A piston, a spring and a cap. held in place by a circlip!. It appears you can not purchase the relief valve components from L/R. They are supplied as a assemble with the front cover. at a cost of (are we sitting down boys and girls) £650!!. However. When I purchased my nice new shiny assemble 18 months ago, when I rebuilt the engine. it appears the relief valve was assembled with only 2 components. The spring and the Cap. No Piston. So in short there was no relief valve fitted to my engine. ummm.

As I understand the oil flow in studying Rave and the front cover drilling's.

The Oil is sucked up out the sump into the oil pump, It then leaves the oil pump into a oil way which has a Tee in it. One goes to the pressure relief valve the other to the oil cooler. The oil then travels through the oil cooler and into the filter housing, then from the filter to the engine. As the oil pressure reaches 55 psi. it overcomes the force of the spring and lifts the piston in the relief valve of its seat and allows the oil to pass directly into the oil filter and then to the engine...

So it is more of a regulator than a relief valve as when the engine is cold and at tick over the oil pump should be producing 30 psi of pressure. and as the revs come up the relief valve opens allowing the oil to bypass the oil cooler.

I still haven't got my head round how it drops the oil pressure if it is a sealed circuit. but maybe someone else could shed some light on this.

Knowing what I do now. I think the only reason my engine has survived for so long is the fact everything was very tight when it was re machined and built. but now it has bedded in this is the end result. Plus the fact that when the revs are up around the 2500 mark the oil pressure is sufficient.

I would be interested to hear from any one how can get hold of the relief valve components. and if anyone else has had the same problem. maybe we are looking at a bad batch of front cover assemblies.

Bryan

Hi All.

It turns out that the front cover is drilled for 2 pressure relief valves and depending on which engine management system you are running (gems or motronic) depends on were the relief valve hides. the blanking plug which I removed next to the oil filter housing is in fact a dummy. the spring is only there to keep the blanking cap hard against the circlip. The actual relief valve is on the other side of the housing by the oil pickup entry port. But you do have to remove the oil pump to get the cap and spring out.

As for it being stuck.................. nope. the piston is moving freely in the cylinder. the spring hasn't collapsed and is fine. so now i am back to what is causing my low rev oil pressure problem.

any ideas?????

Thanks

Bryan

Okay the plot thickens.

I have fitted a brand new front cover and oil pump with both the pressure relief valves fitted.

It has made sod all difference to the oil pressure.

I have run the engine on the semi synfetic oil as i have always done, changed the oil to a 15/40w oil and on the recomendation of richard at turner engineering am now running it on a 20/40w grade oil. all thou it is a little better there is still no oil pressure at 1000rpm and below.

We have now striped the top end of the engine. taken the rocker shaft assemblies off, striped the inlet and removed the valley gasket.

we noticed that the left hand rocker assemble appears to be a different colour to the right hand bank. It is a lot darker in colour. Which suggests to us that there is a oil delivery problem to that bank.

with the oil feed to the rocker shafts exposed we have cranked the engine over the oil which is coming up the oil way and bleading out appears to have a lot of air in it not just the odd bubble but a lot of air to the point that you get a few seconds of no oil.

This has lead us to the conclusion that the oil pump is picking up airenated oil from the sump. not good. and in turn would cause low oil pressure.

as anyone else had this problem with theres????

I have dropped the sump off and removed the oil pick up pipe from the front cover. i cant see any splits or cracks in it but for the sac of £16 i am going to put a new one on it.

Will let you know how i get on.

Bryan

Hi All,

I am really running out of ideas on my oil pressure problems.

This week I have fitted a new oil pickup pipe with new oring, and in cranking it over it appeared to have stopped my air in the oil problem. All i was getting was oil coming out of the heads which feed the rocker gear. So with that sorted I have re-assembled the engine.

I did take 3 of the main bearing journals off to inspect for ware. There spot on. with very light wear. which is what I would expect from a engine with only 15k under its belt.

So with the engine completley reassembled and a workshop pressure gauge fitted. It fired into life and what a difference. It ran so smoothly with no rattles and 15psi showing on the pressure gauge at tick over. As soon as the revs came up the oil pressure was 45 psi at 2000rpm and seams to stop at 55psi on higher revs and when returning to idle back to 15 psi.

However as the engine started to come upto operating temperature I could hear the rocker gear starting to chatter and low and behold the oil pressure had vanished back to reading 0 psi on the gauge.

I am really starting to draw a blank with this so if anyone has any ideas or pointers it would be great fully received.

Thanks

Bryan