Discussion
FunkyGibbon said:
All things being equal, the 45PSI whilst driving sounds right and the 30PSI at idle sounds right BUT ONLY WHEN THE ENGINE IS STONE COLD. 20PSI at idle with the engine hot is nearer the mark.
that's what my 450 does
Same here for my 450. I'm running shell helix ultra 5w40 (as inserted by Leven).
Podie said:
<30 seems a bit low...
On what basis? Maintaining 30PSI in a liquid that's freely moving around in a large volume of air seems quite impressive to me!
Returning to the question, as others have pointed out, there's a lot of governing factors. If the gauge wasn't moving much above 0PSI and/or the oil pressure warning light was lit at any time the engine was running, I'd want to know more. If it was happening in any one of a number of cars I was viewing with the intention of buying, I'd move on to the next one.
Cider Andy said:
<30 seems a bit low...
On what basis? Maintaining 30PSI in a liquid that's freely moving around in a large volume of air seems quite impressive to me!
Returning to the question, as others have pointed out, there's a lot of governing factors. If the gauge wasn't moving much above 0PSI and/or the oil pressure warning light was lit at any time the engine was running, I'd want to know more. If it was happening in any one of a number of cars I was viewing with the intention of buying, I'd move on to the next one.
On the basis that the lubrication of the RV8 is crude at best, so <30 seems a tad low and would give me cause for concern...
If the oil pressure light is on, then it's too late...
I'd be interested to hear V8racing's thoughts though...
>> Edited by Podie on Wednesday 29th March 22:40
Podie said:
<30 seems a bit low...
On what basis? Maintaining 30PSI in a liquid that's freely moving around in a large volume of air seems quite impressive to me!
On the basis that the lubrication of the RV8 is crude at best, so <30 seems a tad low and would give me cause for concern...
I'd be interested to hear V8racing's thoughts though...
OMG not this old chestnut again, there are a bunch of exhaustive threads on this topic.... But for my ha'pence worth, Firstly there are so many variables that its impossible to be prescriptive, for instance:
gauges and senders are notoriously variable and inaccurate.
(as has been mentioned) the type of oil pump, the later crank driven pump on the serpentine engines has much greater capacity and will maintain higher pressures when hot across the rev range.
Oil type , viscosity range and age.
Engine mileage / wear (not necessarily directly related)
Oil temp.
Spec of pressure relief valve spring
For what its worth:
After carefully calibrating my sender and gauge - my serpentine 38A 450 on 24000m with mobil 1 motor sport 10w-50 oil at around 100C registers: 30psi at 850 rpm and a peak of 55-60 at 4000rpm.
For a well used pre-serp with the gear pump, hot idle pressures may well be around 12-15psi and peaking at as low as 35psi when hot, without necesarily indicating a problem.
The real problem is that because of all the unknowns and variables oil pressure per-se is not a terribly helpful guide unless grossly abnormal, and even then really just indicates the need for further investigation - rather than allowing any conclusions to be made.
PS:
the bit about "liquid moving freely in air" puzzles me... oil pressure relates to the pressure in the confines of the main oil gallery just after the relief valve where oil is forced by the pump along the oilways to the main bearings, crank, lifter oilways and then rockershafts, each of these passages ending in (hopefully) quite close fitting bearing surfaces and allowing leakage back into the crankcase. Once back in "air" in the crankcase the oil is only at ambient pressure....
>> Edited by tahiti450 on Wednesday 29th March 23:01
tahiti450 said:
For a well used pre-serp with the gear pump, hot idle pressures may well be around 12-15psi and peaking at as low as 35psi when hot, without necesarily indicating a problem.
Well this bit I can confirm! My pre-serp grif 500 does exactly the above. Peaking around 45 psi when cold. I was worried in the early days, but after having two dealers check it out (with external pressure gauges) and speaking to TVR tech dept., they all said it was normal so not to worry. In fact, the TVR tech dept said you'd be lucky to see 35 when hot, and as long as the warning light doesn't come on at tickover, don't worry!
It's been the same for the 7 or 8 years I've owned it, including a few track days - if something was wrong it would've let go by now!
tahiti450 said:
Nobody forced you to answer: poor old smoorhouse just asked a simple question! Fortunately you did go on to explain some of the variables, which was much more helpful.
tahiti450 said:
PS:
oil pressure relates to the pressure in the confines of the main oil gallery just after the relief valve where oil is forced by the pump along the oilways to the main bearings, crank, lifter oilways and then rockershafts, each of these passages ending in (hopefully) quite close fitting bearing surfaces and allowing leakage back into the crankcase. Once back in "air" in the crankcase the oil is only at ambient pressure....
Do you know at what rate the pump moves oil around the engine (I ask because I don't)? Your description of the oilways is very good and I take your point, but in terms of pumping oil around the engine the system is pretty much a collander: there's a lot of openings from which oil runs back to the sump, unlike, say, a hydraulic braking system which has no openings. Maintaining a pressure of 30 pounds on each square inch in such a system is impressive!
Podie said:
<30 seems a bit low...
On what basis? Maintaining 30PSI in a liquid that's freely moving around in a large volume of air seems quite impressive to me!
Returning to the question, as others have pointed out, there's a lot of governing factors. If the gauge wasn't moving much above 0PSI and/or the oil pressure warning light was lit at any time the engine was running, I'd want to know more. If it was happening in any one of a number of cars I was viewing with the intention of buying, I'd move on to the next one.
On the basis that the lubrication of the RV8 is crude at best, so <30 seems a tad low and would give me cause for concern...
I'd be interested to hear V8racing's thoughts though...
I may be wrong but as I understand it the rover v8 has high volume oil pump rather than a high pressure one and as the oil gets hotter and thinner it can pump loads more of it around the engine with less resistance and therefore a lower pressure which sounds like a good thing within reason?
Mine has 45 psi at cold idle going down to 20ish with the fans on in summer, idleing about 800rpm. It doesn't use much of it even using the 5w40. Pressure on the move 45. All measured on the guage so probably not that accurate.
I don't believe mine has a problem as it runs very well and noise free and has only done 24k with oil changes around 3k intervals.
It's going for a service on Friday so I'll check it out but I've not had any comments from Leven about this and the inspection stated the oil pressure was always healthy. I dare say I could get the pressure higher if I used a thicker oil but after checking out loads of threads on here I'm happy using the 5w40 as I believe it gives better protection from cold and as long as its moving a large volume of oil around the engine its fine.
If the pressure was too high could that be down to a partial blockage somewhere or sludge and not necceserily a good thing? I'm not that 30psi is too high or anything, just wondering.
Cider Andy said:
Nobody forced you to answer: poor old smoorhouse just asked a simple question! Fortunately you did go on to explain some of the variables, which was much more helpful.
Do you know at what rate the pump moves oil around the engine (I ask because I don't)? .......Maintaining a pressure of 30 pounds on each square inch in such a system is impressive!
You're quite right, I only answered out of irresistable compulsion
. My comment wasn't actually aimed at anyone in particular, certainly not "poor old smoorhouse" (my apologies), its just that if I had a quid for every time I'd seen or commented on this one i could probably buy a whole 4l can of Mobil 1.... 
PS. I'll go and look up the flow rate but I think its measured in gallons per minute! You are right about the collander analogy, although that's a bit of an exageration. Because it is fairly leaky the RV8 system is primarily dependant on flow rather than pressure which is why looking at pressure in isolation can be quite meaningless.
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