Oil Pressure Gauge

[Trevor Lover 66]

Hi All - how reliable are the oil pressure gauges - I went out for a test drive the other day in a car am interested in and the gauge seemed to be jumping around between max and the middle of the gauge. The engine ran nicely in all rev ranges and after the drive left the engine running at idle for about 10 minutes and it idled very nicely with no "hunting" at all. Thoughts ?

[phazed]

Readings on the standard gauge can be variable.

The only way to establish correct oil pressure is to connect a mechanical gauge and run the engine up.

Odds are that oil pressure is ok on your fest car but...............you never know

[Trevor Lover 66]

Many thanks Phazed - sound advice

[phillpot]

More likely the sender unit having a bad day than the gauge

[QBee]

Gauge jumping all over the shop can also be bad electrical contact at the sender, though this is more usually going from -5 to 35 and back again as you accelerate and stop.
They generally read between 20 and 40 psi, but the real oil pressure is somewhat higher.

[bobfather]

Gauges vary, senders are very simple mechanical devices that are poor out of the box, let alone after 10s of years under the car. They are an indication only, the gauge should read red/green/red as that's all the system is capable of reporting. The pressure senders have a thin metal diaphragm that fractures and allows oil into the electronics, this doesn't stop it working, it just makes it read wrong, usually low.

As said above, a mechanical gauge is the only way to get a reliable reading, there are several places to affix a gauge, there's a spare blanked off union above the filter that people use for oil temperature, that's where I'd fit one

[Skyedriver]

My first Wedge (not a Chimaera) suddenly showed 0 oil pressure going up a hill, I had a panic and stopped and it returned to "normal".
It then randomly dropped to 0 on a number of occasions without detriment. Was the sender I believe.

[Sir Paolo]

Gauges and senders can cause erratic readings.

I have replaced both over the years.

Whenever I feel oil pressure is dipping, I replace the sender.
Hot oil soon punctures the diaphragm and lowers pressure readings.

A new sender instantly restores a healthier pressure reading.

[Trevor Lover 66]

Thanks Sir - is swapping out the Sender a straight forward job (for the mechanically inept for example.....)

[blacktvr]

Yes this is a very easy job. I changed mine last week. Don't use thread tape because it earths through the body. The photo is of my old one which became erratic. This is the one I used:

100 psi oil pressure sending unit 240-33ohms low 11 psi alarm 1/8”-27 NPT thread.

You do not use the low pressure alarm because the switch on the TVR is separate. The reading may be different to your old one because there are various makes of instruments (gauges) used so you may have to use a resistor in series to get the reading correct.

Gordon

[Sir Paolo]

As said, it’s an easy job, some senders have two connections, some just the one.

Make sure you clean the fitting at the block, and refit the washer to the new sender, otherwise you will have an oil leak.

As also mentioned, it’ll be worth checking the spade connection at the cable - under the car it’s a bit vulnerable.

With all things being well, and assuming the oil pressure relief valve hasn’t been tampered with, you should see about 45psi cold and at revs, once warm.

[Wolvesboy]

Hi,
Sorry to jump on the thread.
i have a 1994 pre serp 4.0 HC - my oil pressure has been rock on 30 since I had the car. (never moved unless engine off). Now has gone up to 50ish and just sits there, never moving again. I changed the oil pressure switch without effect. The sender at Racetech is an expensive 85 quid. Anybody recommend one from elsewhere please?

[Steve_D]

Wolvesboy said:

Hi,
Sorry to jump on the thread.
i have a 1994 pre serp 4.0 HC - my oil pressure has been rock on 30 since I had the car. (never moved unless engine off). Now has gone up to 50ish and just sits there, never moving again. I changed the oil pressure switch without effect. The sender at Racetech is an expensive 85 quid. Anybody recommend one from elsewhere please?

When you say "never moving again" do you mean it stays there with ignition off?
Does it go to 50 before you start engine?

Steve

[Wolvesboy]

Steve_D said:

When you say "never moving again" do you mean it stays there with ignition off?
Does it go to 50 before you start engine?

Steve

Hi Steve, ignition off - gauge off (zero). Ignition/ engine on - straight up to 50ish and never moves even when engine cold, worm, hot, revs etc. I have changed oil pressure switch, now thinking oil pressure sender.

[phazed]

The oil pressure switch his fur the oil pressure warning light.

[Sir Paolo]

Wolvesboy said:

Hi Steve, ignition off - gauge off (zero). Ignition/ engine on - straight up to 50ish and never moves even when engine cold, worm, hot, revs etc. I have changed oil pressure switch, now thinking oil pressure sender.

I had a similar problem on mine - ignition on and gauge went from zero to the opposite end of the scale and stayed there irrespective of revs.

Replacing the sender didn’t solve it, the fault was with the gauge.

Good luck