Oil pressure

[Onzlouk]

Since ive had the cerb back from the its 12k service, warm idle has gone down to around 35 at its worst, whereas before it didnt drop below 40-45, i assumed this may be because of the change of oil. Power put 10w40 in whereas i believe the car had 15w50? in before. Should i be concerned at that and should i swap the oil back or is it ok?
Shes on a 400 mile round trip to Goodwood tomorrow so ill just keep my fingers crossed

[ridds]

35 PSI (if the guage is accurate) is still 2 Bar.

Most engines will run happily at 1 Bar at Idle.

Providing it's good when warm and when your revs are high it should be fine.

Personally I'd run the 10w40 on the road, as I do now and say a 10w50 for the track. Will sap a bit of power but worth it for a bit more protection.

[jesfirth]

I was adved by Topcats to run 15 40 semi synthetic - mine runs at 80 cold (all revs) and 45 hot idle with 65-70 hot when revved. It seems sweet

[Cyclone1]

Onzlouk said:

Since ive had the cerb back from the its 12k service, warm idle has gone down to around 35 at its worst, whereas before it didnt drop below 40-45, i assumed this may be because of the change of oil. Power put 10w40 in whereas i believe the car had 15w50? in before. Should i be concerned at that and should i swap the oil back or is it ok?
Shes on a 400 mile round trip to Goodwood tomorrow so ill just keep my fingers crossed

Onzlouk,

The car had ran the Silkoline 10w-50 and 15w-50 or the Mobil varient all the time I had the car and I think Nige ran the same viscosity. It could be a few things that are causing the lower pressure, the oil is the most obvious as it's just been changed to a different viscosity, first thing I would is order some from Opie Oils and change it, second thing could be the oil pressure relief spring, if they've done a full service then this should have been changed, it used to be a well known weak spot as the original springs used to suffer from fatigue and gradually fail, however mine had one of the new type springs in (which might still have failed), but it might be worth asking power if this was changed. The only other thing they've touched is the tappets. Obvious thing is definitely the oil, I am suprised that Power put in the 10-40 as it's well documented that the higher mileage Cerbs (especially ones running more power) are better suited to the thicker oil.

Hope this helps,
Jules.

Edited by Cyclone1 on Friday 11th July 08:24

[volospian]

I take it that if the relief valve spring is on it's way out, that oil pressure will drop?

[Cyclone1]

volospian said:

I take it that if the relief valve spring is on it's way out, that oil pressure will drop?

Yes.

[HarryW]

Always struggled to understand oils and the common use 10-40 weight and a 10-50 is too thcik. With my limited and simplistic understanding the lower number is its performance at low temperatures and the higher number is its performance at high temps.
Given that I can't see that say a 5-50 isn't the best to use. Someone please explain .

[volospian]

Cyclone1 said:

Yes.

Cool, I may get mine looked at next time it's in pieces. The pressure seems to be slowly getting less and less. Hot idle used to be around 40, now it's nearer 30. Changing the oil doesn't seem to make much difference. The max never ever goes above 60. It's 60 at cold idle, 60 at 3k rpm, once it's warm it's 60 at like 2k all the way round to the red line.

[Cyclone1]

HarryW said:

Always struggled to understand oils and the common use 10-40 weight and a 10-50 is too thcik. With my limited and simplistic understanding the lower number is its performance at low temperatures and the higher number is its performance at high temps.
Given that I can't see that say a 5-50 isn't the best to use. Someone please explain .

Here you go Harry.

http://www.pistonheads.co.uk/gassing/topic.asp?h=0...

Jules.

[Marian]

volospian said:

Cyclone1 said:

Yes.

Cool, I may get mine looked at next time it's in pieces. The pressure seems to be slowly getting less and less. Hot idle used to be around 40, now it's nearer 30. Changing the oil doesn't seem to make much difference. The max never ever goes above 60. It's 60 at cold idle, 60 at 3k rpm, once it's warm it's 60 at like 2k all the way round to the red line.

Do it now please, don't wait cos if it goes you will be in for an expensive fix, from memory you only need a 24mm spanner and the spring of course.

[HarryW]

Cyclone1 said:

HarryW said:

Always struggled to understand oils and the common use 10-40 weight and a 10-50 is too thcik. With my limited and simplistic understanding the lower number is its performance at low temperatures and the higher number is its performance at high temps.
Given that I can't see that say a 5-50 isn't the best to use. Someone please explain .

Here you go Harry.

http://www.pistonheads.co.uk/gassing/topic.asp?h=0...

Jules.

So a 0-40 10-40 is probably good for Cerb then, as most figures I've read on here reckon the oil rarely gets above 100. Anyone with an oil temp gauge care to state what temps the oil hits on the track or with spirited driving in summer. I know the misses TF hits around the 120 mark with spirited driving.

[Cyclone1]

HarryW said:

Cyclone1 said:

HarryW said:

Always struggled to understand oils and the common use 10-40 weight and a 10-50 is too thcik. With my limited and simplistic understanding the lower number is its performance at low temperatures and the higher number is its performance at high temps.
Given that I can't see that say a 5-50 isn't the best to use. Someone please explain .

Here you go Harry.

http://www.pistonheads.co.uk/gassing/topic.asp?h=0...

Jules.

So a 0-40 10-40 is probably good for Cerb then, as most figures I've read on here reckon the oil rarely gets above 100. Anyone with an oil temp gauge care to state what temps the oil hits on the track or with spirited driving in summer. I know the misses TF hits around the 120 mark with spirited driving.

Yes. But reading the article it states that a 50 grade oil will still be thicker at say 90 degs than a 40 weight, this will result in a higher oil pressure reading being given on the gauge. The article refers to "modern" engines......the ajp most certainly isn't modern.

Jules

[HarryW]

Cyclone1 said:

HarryW said:

Cyclone1 said:

HarryW said:

Always struggled to understand oils and the common use 10-40 weight and a 10-50 is too thcik. With my limited and simplistic understanding the lower number is its performance at low temperatures and the higher number is its performance at high temps.
Given that I can't see that say a 5-50 isn't the best to use. Someone please explain .

Here you go Harry.

http://www.pistonheads.co.uk/gassing/topic.asp?h=0...

Jules.

So a 0-40 10-40 is probably good for Cerb then, as most figures I've read on here reckon the oil rarely gets above 100. Anyone with an oil temp gauge care to state what temps the oil hits on the track or with spirited driving in summer. I know the misses TF hits around the 120 mark with spirited driving.

Yes. But reading the article it states that a 50 grade oil will still be thicker at say 90 degs than a 40 weight, this will result in a higher oil pressure reading being given on the gauge. The article refers to "modern" engines......the ajp most certainly isn't modern.

Jules

At what point is the oil too thin on the hot side though, reading the article it reckons 40 weight is good up to 120degs but the oil is down to 8.8cst but anymore then you should be using a 50 weight, which should be above 10 at that point and will maintain pressure better (although flow is probably more important as a blockage can give you high pressure ). It also says you should be using the one that has the lowest (second) number you can get away with as it is thicker and will increase drag and cost power. Which takes me back to the question, what temperatures are people seeing on Cerbs, I've not heard of anyone reporting temps in excess of 100 for oil yet, let alone 120. Yes the pressure will drop with temp but so long as it stays north of say 30psi at tick over and 60+ above that I can't see it being an issue, can you . Unless the temps are reported as being in excess of 110-120 I tend to think a high quality 0-40 has to be the one to have in a Cerb.

[Cyclone1]

HarryW said:

At what point is the oil too thin on the hot side though, reading the article it reckons 40 weight is good up to 120degs but the oil is down to 8.8cst but anymore then you should be using a 50 weight, which should be above 10 at that point and will maintain pressure better (although flow is probably more important as a blockage can give you high pressure ).

Correct, but like I said the passage referes to modern "normal" engines not race derived AJP's. I don't think we know the answer as to what temperature on an AJP does the hot side of the oil viscosity become compromised, from what I can understand I would say that on a 30k + mileage Cerbera running at upto 90-95 degrees oil temp then a 50 weight would ensure a better oil pressure reading than a 40 weight, the critical operating point on an AJP may be 90 degrees and not 120 (eg less than) as stated for the modern engine, ultimately it may not perform as well due to drag etc but I think this would be hard to notice.

Jules.

[ridds]

The Cerb and it's wonderfull oil cooler setup over-cools the oil in UK normal road conditions.

For a general use road car then 10w40 is fine imho.

Anyone who does spirited driving, and I mean actually using all the revs often, or visits tracks, should be using something a little thicker for a little more protection when the pressure drops off at high temperature.

[alderley]

ridds said:

The Cerb and it's wonderfull oil cooler setup over-cools the oil in UK normal road conditions.

For a general use road car then 10w40 is fine imho.

Anyone who does spirited driving, and I mean actually using all the revs often, or visits tracks, should be using something a little thicker for a little more protection when the pressure drops off at high temperature.

My 1998 4.5 has done 24k miles and until a year ago used TVR's recommendation of 0W 40 Mobil 1. It has done occasional trackdays and many speed championship events, revving to over 7k. Last winter the oil looked less clean than usual and I changed to Opie's recommended 5W 40. With a new oil pressure spring, at warm tickover pressure is 40 psi and about 65 at about 3k revs. My engine has not blown up yet! I suspect that a thin oil is really important to protect the engine on start up in winter. I only use high quality synthetic oil; the extra cost is like an insurance policy for my peace of mind.