Oil Pressure

[petticd]

Hi, I noticed that the oil pressure on my 340 was slow to biuld up and would drop or wave about occassionally on start up. I have replaced the oil, filter and the relief valve along with the oil pressure sender. However, I still feel the pressure is slow to biuld up when starting - maybe 15-30 seconds to reach 40psi. Is this excessive?

The engine holds good pressure when hot and driving, it has alway's had 40psi and now with the new sender it goes up to almost 60psi when cold and holds around 40 when hot and at a fast idle.

How long should it take to reach a good operating pressure when starting?
Has anyone else experienced this, if so what was the fault? Thanks.

[webman]

The O/P guage is of the thermal type and is notoriously slow.

I don't think 15 seconds is unusual, I will be moving my 340 today so I'll time it, and report back.

[webman]

Well I did take my 340 out for a spin. It took 35 seconds to reach 50psi my normal cold idle pressure. The effective word here is COLD. My garage is always very cold, probably about 12 Celsius.

After the spin, I left the car outside for a few hours and when I decided to put it to bed, it took less than 15 sec to reach idle pressure.

[petticd]

Thanks for your input, I decided to fit a new oil pump as good measure. This has made some difference especially when cold, I would estimate I get up to 40 PSI in around 15-20 seconds. When running at 1500 revs I now also get 60 PSI (off the gauge in fact) hot or cold and a good 40 PSI on idle. Regards

[ManxNeil]

Just had my 3.8 Mk2 on the road with a rebuilt engine (by VSE) and all seems well, except the oil pressure shows 25 and doesn't vary. Oil level remains good, with no suspicious smoke or leaks and the temperature is fine. Both the sender unit and the gauge are brand new from the same Jag specialist, but a friend has suggested that they may be mis-matched.

Before I start struggling to take the sender off has anyone else come across this problem?

[Martec]

Hi Neil,

The electronic oil pressure sender and gauge are notoriously inaccurate, to the point that it used to be said not to worry about low oil pressure. The club commisioned a supplier (possibly SNG Barratts) to produce a reasonably accurate pair (sender and gauge) as they must be compatable.

I had a spare mechanical (oil capiliary pipe) gauge and connected it along side the original electric gauge. They did not start at the same pressure or advance at the same rate and so did not finish at the same pressure.

I concluded that the electric one was cr*p and remounted the mechanical one in the lower dash near the radio (I didn't fancy stressing the tube when opening the dash to work on the electrics) and a 2" electric clock in place of the oil pressure gauge.

Just to state the obvious, good oil pressure is dependant on a number of factors, a good oil pump (I fitted an XJ6 pump), a clean filter (I fitted a proper spin on canister filter), a good condition pressure relief valve and spring (new is best) and all the engine bearings within tolerance. Any of these in poor condition will lose oil pressure.

Using the mechanical gauge I timed the pressure build up when changing over from 20/50 to 10/40 oil, no change.

Hope this helps

Brian

[ManxNeil]

Thanks, Brian, all very useful.

I believe the pump is new and I've converted to the spin-on filter. A mechanical pressure guage may well be the way to go. Your comments on the pressure relief valve are particularly interesting, though, as it was our Region's monthly meeting tonight and, when discussing the problem, one of our members there also stressed the need for a good valve and also mentioned the spring, so that's going to be my first port of call.

Thanks again,

[ManxNeil]

By way of an update, the new pressure relief valve components went in, but no change in the reading.

A check of the invoices I've collected for the car (they go back a long way) revealed that I was lying when I said I'd bought the sender and gauge from the same specialist. Though the sender came from a Jag specialist I purchased the gauge from the 'Smiths Classic' range supplied by Caerbont Automotive, assuming it would be compatible. However, the gauge they supplied reads up to 100 where the correct Mk2 gauge should read up to 60. As Brian says, the Club does indeed supply a matched sender/gauge and this has done the trick - a good 55 at cold on a newly-rebuilt and tight engine.

As an aside, the service from JEC Spares was excellent - the package arrived less than 24 hours after placing the order. (We're used to couriers assuming the Isle of Man is on the dark side of the moon and charging us twice as much for a service three times slower - don't let Brown or Cameron destroy the Royal Mail!)

[Martec]

ManxNeil,

Nice to see you have had a good result.

Brian

[pnegre]

Hello everyone (if you're still on line after the years have passed since the last post !!),

When my XK150 (engine redone 35000 miles ago) shows perfect cold/idle 70psi, and hot/3000rpm 45psi, and hot/idle30psi, I have NOT AT ALL the same results with my 3.4 MK2 (100.000 miles from new, and only upper engine lately overhauled); even with fresh Millers 20-50, new filter, absolutely no smoke whatsoever when driving, even pushing revs to check, I have worrying results: cold start, sometimes 0, sometimes 40 at idle; first run and during 1/2 h, 35-40 psi at 3000rpm, or 20 at 2500rpm; after runs, say of 20 miles, idle drops to 0-10 psi, and at normal speeds and 2000-2500 rpm, no more than 20psi. Sometimes idle jumps to 50psi (!) for a few seconds and redrops to 15 psi !! why !!??

I am puzzled: could it be the sender (both parts are new, not same source though)?, the relief valve /spring ? (checked previously!...), the filter type ?, or...my engine bearings, but no smoke while driving, and good compressions on 6 cylinders !!

thanks for your help, but my first idea was to (1) test again with mechanical pressure gauge (previous results showed better PSI than gauge) , (2) fit mechanical gauge as on the XK !!

Pascal
JEC Member n°4575

[piman]

Hello Pascal,

a variable reading would indicate that there is an intermittent electrical connection somewhere?
Personally I would go with your second choice and fit a mechanical gauge.
Incidentally, referring to one of the early posts about a 0 to 100 psi gauge, originally that is what Jaguar fitted but because the correct running pressure looked low on the scale, a 0 to 60 gauge was fitted (1960).

Alec