Good morning. I recently purchased a 1969 roadster in well preserved condition, completely been through front to back. Unfortunately the oil pressure gauge is not functioning properly(which I read is quite normal). It is a 60psi gauge and will read properly(40+ #'s) upon starting yet drops to zero at idle and erratic at best while running(jumping from 20 to 40ish). I have checked with a pressure gauge and the pump is functioning properly with good pressure, however I am considering some alternatives given this is a common issue yet a have a couple of questions.


First, is the issue typically the gauge or the sending unit? Or is it simply a combination of the two? Can it be corrected with reliable results?


Second, has anyone ever fitted an aftermarket mechanical gauge? If so, is there a spot to run the line without putting a new hole in the firewall?


Thank you in advance.


cheers,
Geoff

 

The electric oil pressure gage in a jag relies on a good ground, both at the gage and the sending unit Soooo.. lower the center of the dash and clip one of those radio-shack aligator leads on the case of the gage (make sure it doesn't touch the connecting terminal) and the other end to a good ground on the back of the firewall. Then take another one of those test leads and clip one end to the sending-unit body case and the other to a good ground.. If this cures the problem then you know you have to tighten the sending unit or fix the grounding of the gage by sanding the "U" bracket that holds it in place.
If this doesn't fix the erratic readings you could try a new sending unit, and......
if this doesn't cure the problem find another Jag gage........ If you try to replace
the gage with a mechanical one I haven't seen a unit that is the same appearance as the Jag unit, although a Triumph TR3a unit will fit it has a max range of 100lbs.

 

Thank you, I am going to give it a shot today and will let you know the results.

 

Further to felinecat's comments, the operation of the Oil Gauge can be checked by shorting the cable attached to the OP sender to Ground. If the gauge it working, it will peg out to the maximum reading on the gauge.

Regards,

Brent

 

thanks this is helpful to me as well. also a 69 s11

 

Sorry for the delayed followup for this. I cleaned all contacts, have solid ground, etc. and it is the gauge itself and will be replacing shortly. Thanks again for the help.

cheers,
Geoff

 

my 69 came with a very old op sending unit. start up op was 45 and dropped to about 25 when warmed up. ted at jag Denver suggested replacing the sending unit. I carefully ordered a new unit for a 69 sii, 4.2 from terry's jag and installed. now start up op is 100+ and drops to 60-70 after engine is hot.
seems a bit unrealistic to me.
any ideas on this one?

 

I hooked a0 to 100psi mechanical gage to the fitting beside the oil filter on my 4.2,
with my rebuilt engine running 20w50 oil in 70degree ambient farenheight weather,
I have the stock oil pump and have not altered the oil pressure relief valve.
Start up 75 to 85lbs drops to 55 to 65 when warm ( 185 degrees Farenheight).
If I try to set the idle down to 500rpm 40lbs warm, normal idle 750rpm 60psi
With electronic gages and sending units I have got 25lbs to 100psi readings, this is two
older gages, one new one and 3 different sending units !!! I like my old fashioned mechanical gage. I also screwed in a new industrial dampened mechanical gage to the engine and it confirmed my dash -mounted mechanical gage.

 

My 1966 XKE oil gauge is reading 60+ except in idle. Is that an issue?

 

Not really. Mine is at 60+ most of the time. When REALLY hot, it comes down to about 50-55. You may have the pressure relief valve stuck, but I wouldn't worry too much at those readings. Do you have the original sender type guage or a modern mechanical replacement? If it's the electrical sender type, the reading is probably wrong anyway.