Oil Pressure Advice

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andrewk
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#1 Oil Pressure Advice

Post by andrewk » Tue Jul 14, 2015 5:05 pm

Hello All,

I need some advice/help on oil pressure please.

I've read through the archives on here and on the net, but am a little confused on different pressure readings.

My car's an automatic and had its engine rebuilt. Its done about 350 miles since completion last August.

Recently after around 7 to 10 miles travelled, the oil light comes on whilst at idle waiting in traffic or at the lights. The gauge too is consistent with it reading very low at the same time - not quite on zero, but not far off.

Subsequently, the person who rebuilt the engine, swapped over the oil pressure relief valve suspecting it was sticking for another, albeit this was a used unit that was known to be working previously fine. Nevertheless, this did not cure the problem.

On his suggestion, I then changed the oil filter & running in oil for Castrol Classic 20W/50. Unfortunately, this too didn't cure the problem either, with the light coming on at about the same as when the problem first occurred.

We've subsequently had a few issues related to the oil pressure and other concerns of the car and are not on the best of terms - regrettably...

I know too that the sender unit and pressure switch are notorious unreliable and the next step was to fit a mechanical gauge. I have since borrowed one and tried to mimic the same conditions, albeit on my drive.

The readings I got are:

60 Psi at cold starting.

20 Psi at 2000RPM - operating temperature

8 Psi after 30 minutes idling, car in "D" at 650-700RPM

The temperature sits between "A & L" and when I blip the throttle, car hangs at 10-12 Psi.

What I'd like to know, is 8 Psi acceptable?

I've read conflicting information on the net that the V12 is happy at 5 Psi, whilst some say 20 Psi which has left me confused. Also, at what pressure should the switch activate the warning light on the dash i.e. meaning my switch is off?

Any advice is appreciated.

Many thanks,
Andrew
73, OTS

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Sjmmarsh
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#2

Post by Sjmmarsh » Tue Jul 14, 2015 5:53 pm

Andrew

That sounds a bit too low - mine reads 40psi when in D an at 2000 rpm, dropping to around 15psi when at idle and hot. Warning light doesn't come on other than before I start the car.

As your gauge and warning light are both telling you you have low pressure, you need to do some investigation - don't ignore it.

Steve
Steve
1973 S3 v12 2+2 1S52113BW

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MarekH
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#3

Post by MarekH » Tue Jul 14, 2015 5:57 pm

Dear Andrew,

First check that you actually have any oil in the car.

It does rather sound as though you don't have much by way of oil pressure and I'd be worried by that.

There are two spring valves in the oil system. The main one is a very strong spring that takes about 70psi to push open. A spring is just a spring and it doesn't care whether it is hot or cold - it'll still take 70psi to push it open.
The second is a tiny spring valve that simply bypasses the oil filter should it be blocked - it doesn't affect the operating pressure which is generated by the oil pump (or not as in your case...).

The person who rebuilt the engine clearly doesn't understand much if they think that replacing the big relief valve will help:- the relief valve simply puts a cap on the oil pressure, typically around 70psi whilst driving normally. Put another way, your oil pump should be capable of providing pressure well in excess of 70psi once above idle speed (hot or cold) and the big valve simply cuts in to limit how high that pressure can get. It should have no bearing on anything if pressure is below the cut-in level (no pun intended).

When idling, the oil pressure will be lower, typically 40-50psi once warmed up, so it won't be capped, but as soon as you dab the throttle, expect it to go to 70psi and stay there. I don't know exactly what pressure the oil light is set to, but connecting up a garden insecticide sprayer in place of oil pressure sender and pumping the handle a few times is enough to extinguish the oil light, so I am guessing you have 5psi or less at idle. I'd start to worry, as the oil light should never come on.

For an early 1971 car, this is measured at the main oil gallery; for later cars it is measured after the main bearings on the way up to, but before the camshafts.

Clearly 8psi hasn't resulted in a catastrophe yet, but it isn't anywhere close to where you'd expect for a rebuilt engine. I would say you are at least 30-35psi short of where you expect to be once hot.

By way of comparison, my rebuilt engine from cold maxes out at 70psi on the starter motor within a couple of seconds - I am using the same oil as you. I have a mechanical gauge fitted.

The electrical sender fitted may not be the right one for the car/gauge so may not be accurate.

kind regards
Marek

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christopher storey
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#4

Post by christopher storey » Tue Jul 14, 2015 6:49 pm

I am not a V12 man, but even in general terms it sounds very low. There are some engines which are designed for low pressure - the Rover V8 is a classic example with a running pressure of 28 lbs hot and idle of perhaps 12 lbs hot, but from what Marek says the V12 certainly is not such an engine . I would look for a pressure loss area such as a fault in gaskets for the oil pump or the oil filter , possibly allowing a leak either on the delivery side or even on the suction side of the pump . I am not conversant with the V12 filter, but on the 6 cylinder cars there are a number of different gasket arrangements between filter body and block, and if the wrong gasket is used it can produce symptoms of the sort you describe and will in the end lead to serious damage. Also, despite what has been said , and the change of relief valve , I would look carefully at both the ball and the spring, and perhaps moreso given the change of valve, the seating of the ball, to see that there is not something like a bit of swarf or damage to the seating which is just preventing the ball from giving a good seal . This will produce precisely your symptoms : moderate pressure when the oil is viscous, and very poor pressure when the oil gets thinner

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Heuer
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#5

Post by Heuer » Tue Jul 14, 2015 7:42 pm

I had a sudden drop in oil pressure after some service work on my S1. Turned out to be a bit of silicone sealant holding the relief valve open.
David Jones
S1 OTS OSB; S1 FHC ODB
1997 Porsche 911 Guards Red

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abowie
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#6 Re: Oil Pressure Advice

Post by abowie » Tue Jul 14, 2015 11:09 pm

andrewk wrote:Hello All,

I need some advice/help on oil pressure please.
All of the electronics used to measure oil pressure in the Jag engines are potentially suspect.
Fit a mechanical (Bourdon) gauge known to be accurate.
As Marek says, make sure the engine has the correct amount of oil in it. I would drain the iil and refill the car with the correct amount.
Then you can get an objective measure of what the oil pressure actually is.
If it is as low as your post suggests I too think it is too low. I have no personal experience with the V12 engine so I can't give advice there but if it were me I'd be expecting the mechanic to be using new parts to replace suspect ones..
Andrew.
881824, 1E21538. 889457. 1961 4.3l Mk2. 1975 XJS. 1962 MGB
http://www.projectetype.com/index.php/the-blog.html
Adelaide, Australia

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andrewk
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#7

Post by andrewk » Thu Jul 16, 2015 5:43 pm

Thank you everyone for your advice.
Yes, the car does have oil to the correct level and the oil pressure used to be in line with what Steve's car is.
I won't be driving the car until its sorted - I just hope it's not going to be an engine out job.
Will keep you posted.
Thanks again for the tips and replies.
Andrew
73, OTS

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#8

Post by Sjmmarsh » Thu Jul 16, 2015 11:11 pm

Andrew

My thoughts were that it sounds like the pump could be the problem or you have a leak somewhere that stops the oil getting up to pressure. I had a Google and found this - sounds very similar to your situation:

http://www.britishcarforum.com/bcf/show ... ew-rebuild

Steve
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1973 S3 v12 2+2 1S52113BW

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#9

Post by andrewk » Sun Jul 19, 2015 8:41 pm

Thanks for this Steve, I appreciate it.
Article is an interesting read.
Car's going to be looked at by the engine builder, however due to various reasons not until September.
I'll post an update once we have a diagnosis.
Andrew
73, OTS

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Lambo911
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#10

Post by Lambo911 » Thu Oct 08, 2015 12:30 pm

Did you find the problem Andrew?

My car runs good oil pressure about 50-70 typically but I have found that after a long high speed run it can drop to about 40, even when being reved and on idle at 600 rpm the gauge is showing about 15-20 and the oil light occassionally flickers.

I'm running classic 20-50 mineral oil and I think it is just getting too hot. The water temperature is fine by the way.

I was wondering if a change to a semi synthetic would be better or even putting an oil cooler in somewhere?
Richard
____________
1972 S3 2+2 - Black with Red leather, 4 Speed and Wires
1966 S Type 3.8 MOD - ex South Africa
1994 XJS V12 coupe - 59,000 miles

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#11

Post by andrewk » Fri Oct 09, 2015 6:04 pm

Hi Richard,

Thanks for asking.

The car is currently with the engine builder being looked at. Due to both our separate commitments, its only gone back to him recently.

Fortunately we're back on speaking terms and working a way forwards.

Once he's found the issue with the oil pressure and rectified it, I'll post an update to the forum.

In regards to your oil choice or idea of adding an oil cooler, I'm not the best qualified to answer this. Hopefully someone will chip in on this thread and give you some ideas.

Best regards,
Andrew
73, OTS

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#12

Post by PeterCrespin » Fri Oct 09, 2015 9:40 pm

Lambo911 wrote:Did you find the problem Andrew?

My car runs good oil pressure about 50-70 typically but I have found that after a long high speed run it can drop to about 40, even when being reved and on idle at 600 rpm the gauge is showing about 15-20 and the oil light occassionally flickers.

I'm running classic 20-50 mineral oil and I think it is just getting too hot. The water temperature is fine by the way.

I was wondering if a change to a semi synthetic would be better or even putting an oil cooler in somewhere?
Low OP is common on v12s.

Pete
1E75339 UberLynx D-Type; 1R27190 70 FHC; 1E78478; 2001 Vanden Plas

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#13 Re: Oil Pressure Advice

Post by andrewk » Mon Nov 06, 2017 5:58 pm

Hello All,

Firstly my apologies for the lengthy time its taken for an update on this thread.

I have had the car back for a year, but thought it wise not to post anything on-line until I was confident issues had been resolved.

After getting the car back to the engine builder, he stripped the engine down and could not find any reason for the drop/lack of oil pressure. Strange as this is, I had to take his word on this as realistically, I had no means to disprove him and he was carrying out the work under his warranty. In fairness, he could have just said a seal had gone wrong to cover himself.

I could of course collected everything and taken the engine to another mechanic/specialist for appraisal, but I did not want to go down this route yet. Furthermore I visited him regularly whist work was in progress and therefore could see he genuinely was trying to put things right.

In the end, at his expense he changed out all the main bearings concerned - even though all of these had been replaced during the initial rebuild with new and still measured perfectly in tolerance.

The oil pump was a used unit, but it too measured in tolerance. However I decided to speak to Rob Beere and I purchased one of his uprated oil pumps. Rob also changed (for FOC) the spring in my pressure relief valve for one of his. I appreciated his words of advice too.

We also swapped from Castrol Classic to Valvoline 20/50 mineral - although I have subsequently changed to Millers Classic Sport 20/50 semi synthetic.

The good news is the car’s oil pressure is fine. When cold starting its roundabout, or just below 80 and soon droops to 70ish, whist driving and hot between 50-40. In traffic at 5mph, just below 20psi, but soon jumps up once accelerating. I know I haven’t quoted RPM etc.. however this is typical of 40 mile trip with outside temperature in the mid 20c’s

What caused the low oil pressure, I’ll never know. However I have no regrets in changing out the oil pump or uprating the pressure relief valve’s spring. In hindsight this should have been done during the initial rebuild.

One observation I have found is that the car performs better since I swapped over to Millers Classic Sport. I did read that some are weary of using semi synthetic for various reasons (including leaks), however I have no issues and there is a different feel. Oil pressure is slightly stronger too.

Fingers crossed it lasts !

Warm regards to all,
Andrew
73, OTS

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#14 Re: Oil Pressure Advice

Post by Adamski » Fri Nov 24, 2017 8:02 pm

I don't believe the oil was ever the problem. I ran my V!2 on Halfords blue own brand for years with no problem. I'm suspecting grit under the relief valve had it passing or that notorious sender unit that in another post a David Manners replacement worked great. The oil solution is just too good to be true and you know what they say.
Adam
S3 V12 E Type FHC Manual 1972-owned since 1978
1957 XK150 since 1976

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JJC
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#15 Re: Oil Pressure Advice

Post by JJC » Sat Nov 25, 2017 10:26 pm

Always figure one lbs. of oil pressure, for every 100 rpm's. Also, replace , certainly in a V12, the Smiths electric sender and gauge, with a mechanical Smiths set up. Easy, and accurate.
John

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