Oil pressure gauge

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The Judge
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#1 Oil pressure gauge

Post by The Judge » Mon Jul 26, 2021 5:47 pm

Hello!
This is my first post as I just joined. I have a primrose ‘67 OTS which I’ve owned since 1976.
The oil pressure gauge, original to the car, reads 40lbs upon starting , then drops as the engine warms. At a reading of 50 degrees centigrade it is at 20lbs and at 70 degrees it at 5, idling at zero. I’ve had the oil pressure and compression checked by a mechanic and am told both are fine, and the car continues to run fine as well,
but it is unnerving.
Any suggestions would be appreciated.
Cheers!

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mgcjag
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#2 Re: Oil pressure gauge

Post by mgcjag » Mon Jul 26, 2021 5:54 pm

Hi...welcom to the forum...whats your name...please try to put it with your car model in the signature area....the electrical sender/guage are well known for just giveing an indication of pressure and are far from acurate....how did your mechanic check your oil pressure....just by looking at your guage or with a proper wet oil guage.....if you want an acurate reading you will need to fit a wet guage.....many already have....Steve
Steve
69 S2 2+2 (just sold) & Building a C type replica, 1960 xk150fhc

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christopher storey
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#3 Re: Oil pressure gauge

Post by christopher storey » Mon Jul 26, 2021 6:20 pm

The gauges themselves are not all that unreliable, but as already stated the senders are notorious for inaccuracy, and replacements tend to be even worse than the originals. SNGB do a kit which seems very popular for converting to a "wet" gauge and IIRC this looks just as an original would

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chrisfell
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#4 Re: Oil pressure gauge

Post by chrisfell » Mon Jul 26, 2021 7:45 pm

I have a selection of senders, each reading a different range of values.
The one on the car has been reasonably consistent since fitted, but even it has ‘moments’. On the same journey it can read under 40lbs and almost 50 lbs at the same revs, depending on how it feels.

Others swear by a mechanical gauge, but I am happy with the OE gauge using the following quick check.

If the oil pressure drops according to the gauge, and the engine does not get noisy, it is probably the sender. So to check, with the engine just idling, I lift the bonnet and remove the oil filler cap. If the exhaust cam is awash with running oil (which it always is) there is nothing wrong with the lubrications system.
Chris '67 S1 2+2

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malcolm
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#5 Re: Oil pressure gauge

Post by malcolm » Tue Jul 27, 2021 7:28 am

Hi and welcome to the forum. As said above, the problem is quite likely the sender. I had one that just read zero all of a sudden, and another that gave false low readings and nearly got me to do an engine re-build. i fitted the SNG mechanical guage and now I can rely on the readings, which are always good. I'd get the mechanic to check the pressure when hot properly with a wet guage, and if they are ok change the guage. I like the re-assurance of seeing good pressures all the time as I drive along!
Malcolm
I only fit in a 2+2, so got one!
1969 Series 2 2+2
2009 Jaguar XF-S
2015 F Type V6 S

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christopher storey
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#6 Re: Oil pressure gauge

Post by christopher storey » Tue Jul 27, 2021 8:53 am

chrisfell wrote:
Mon Jul 26, 2021 7:45 pm
So to check, with the engine just idling, I lift the bonnet and remove the oil filler cap. If the exhaust cam is awash with running oil (which it always is) there is nothing wrong with the lubrications system.
I agree that if the engine is not making untoward noises the likelihood is that there is nothing seriously amiss. However, I must respectfully disagree that oil reaching the top of the engine is of itself an indication that all is well : from experience ( filling the engine with a garden sprayer ) no more than about 4 lbs/sq.in pressure is needed to achieve this, and that is not sufficient to protect a running engine

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chrisfell
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#7 Re: Oil pressure gauge

Post by chrisfell » Tue Jul 27, 2021 9:24 pm

Agreed that the presence of oil is not an indication of sufficient pressure, but that isn’t what I said/wrote.
Chris '67 S1 2+2

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