When I first start my V8 P6 from cold, the oil pressure is very good, reading about 3/4 of the way up the gauge. As it gets warm though, at tickover, it drops; this I know is normal, oil gets thinner as it warms up, but after a few mins at tickover, engine up to normal running temperature, it drops enough to just put the oil warning light on. If you gently blip the throttle, it jumps back up to about 1/2 way on the pressure gauge; the oil warning light only just comes on at tickover, with a warm engine. There are no untoward sounds from the engine, sounds silky smooth. I'm wondering if the oil pressure sender may be reading a bit low. The car ticks over at an indicated 800rpm on the tacho. I'm not overly concerned, but am uncomfortable with a warning light coming on at tickover. Is this normal??
Is this normal?
- Thread starter V8P6B
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NickDunning
Active Member
V8P6B said:
Being a non-V8 head I'd like to know the answer to this as well as I've recently sold a V8 which had similar characteristics, although the oil light did not come on at idle.
I've been told that the engine is basically healthy if you're getting a 30lbs psi reading at 2000 revs. Can someone confirm this?
Thanks
Nick
The oil pressure switch will activate the oil warning light on the dash when the oil pressure as it leaves the pump and flows back into the engine drops to within 8 to 10psi or less.
When the V8 is at normal operating temperature, say 80 to 85 degrees C, and running 20W-50 engine oil, oil pressure will register at idle with a healthy engine around 15 to 20 psi. At 2000 rpm, 30 to 35 psi would be acceptable to me.
Assuming the pressure transmitter is working correctly, oil pressure is lost through primarily through wear in the oil pump, bearings, especially those of the camshaft and rocker shafts.
If the oil warning light is coming on at idle, then for me the engine would be looking for a rebuild in the not too distant future. Look inside the oil filler cap. What colour do you see? Anything resembling black is not good for long term longevity.
Ron.
When the V8 is at normal operating temperature, say 80 to 85 degrees C, and running 20W-50 engine oil, oil pressure will register at idle with a healthy engine around 15 to 20 psi. At 2000 rpm, 30 to 35 psi would be acceptable to me.
Assuming the pressure transmitter is working correctly, oil pressure is lost through primarily through wear in the oil pump, bearings, especially those of the camshaft and rocker shafts.
If the oil warning light is coming on at idle, then for me the engine would be looking for a rebuild in the not too distant future. Look inside the oil filler cap. What colour do you see? Anything resembling black is not good for long term longevity.
Ron.
If you read the handbook, it says that if the oil light comes on at tickover when hot it's acceptable providing you have a reasonable reading on the guage, but the guage should really be checked against a master guage. When hot the pressure should be 30-40 psi at 2400 rpm, and those figures obviously give scope for some variation. The trouble is that anyone not aware of this assumes that the engine is worn because of the light coming on at idle, which is not always the case. Ultimately I'd fit new big end and main bearings as a cure, which always bumps up the pressure, and run the engine on 20/50.
webmaster
New Member
I know the V8's run lower pressure, but as a reference, my old 2.2TC had problems with the warning light coming on at idle, and I was told to ignore it, after 200 miles the big bearings were knocking "very" badly, when I dropped the sump the crank was basically scrap...... (my excuse is it was my first P6)
However you may just be running too thin an oil.
However you may just be running too thin an oil.
4 cyl engines are different in that they have a warning light sender that comes on at a far higher pressure (over 20psi IIRC) so fit the wrong one or ignore it at your peril. They run a high pressure system (hence the guage going up to 100psi as opposed to the V8's only going up to 60psi) whereas the V8's run a high volume system but at a substantially lower pressure. (Better still with the higher volume SD1 pump.)
The cure is still the same, providing the ends aren't knocking and damaging the crank, change the shells. (See "Brian-Northampton's blog) It should stop the bottom chain jangle at the same time.
The cure is still the same, providing the ends aren't knocking and damaging the crank, change the shells. (See "Brian-Northampton's blog) It should stop the bottom chain jangle at the same time.
Mad_Dan_Eccles
Member
harveyp6 said:
I think the thing to watch is for a change in the light's behaviour which is an indicator of engine state.
If it's on or flickering at idle and stays that way and the gauge is reading within the acceptable limits, then you are usually OK. However if a flickering light chages to on, or it stays on at higher revs this can be a sign of incipient wear in the engine or oil pump. However before you start stripping the engine, do check the oil pressure switch - these have been known to fail and it's a lot cheaper to replace the switch than to rebuild the engine
Cheers guys, I'll check the oil pressure with a master gauge, seems sensible. I've been moving the car about a bit lately, (its not on the road at the moment), as I'm having a garage built, so the car's been shunted about & that may have been a factor, although I always tend to leave it running to get the oil circulating and warmed up. It may be the wrong grade of course, I haven't changed it yet, the previous owner did that just before I bought it. Another thing is of course, it may be just ticking over a bit slow, if you just pick the revs up to 1000rpm (indicated), the oil pressure shoots up to half way on the gauge. I'll have a better idea when the car's on the road, I think. (Hopefully not long now, although I might wait til springtime.. 8)