High Oil Pressure

High Oil Pressure

Author
Discussion

kris450

Original Poster:

518 posts

171 months

Saturday 14th May
quotequote all
Hoping to get a little advice of possible chaps.

Just finished refitting my rebuilt engine from V8D. All went smoothly it seems except that when running for the first time I have insanely high oil pressure. As in its reading off the top of the scale.

Engine sounds good with no obvious issues.

I’d rather not carry on the cam running in process of course until this is sorted.

Could this be a faulty oil pressure sender ? It wasn’t changed during the rebuild. Any other obvious causes for it ? All wiring/earths are good and checked.


Edit: Now on further inspection it seems as if the gauge is reading about 10psi without the engine running but the ignition on !!

Edited by kris450 on Saturday 14th May 15:52

bobfather

11,069 posts

232 months

Saturday 14th May
quotequote all
Is it a new pressure sender? If so it could be ranged for a different gauge, sender and gauge need to be matched

kris450

Original Poster:

518 posts

171 months

Saturday 14th May
quotequote all
bobfather said:
Is it a new pressure sender? If so it could be ranged for a different gauge, sender and gauge need to be matched
No, its the same as before which never showed any issues. It was on the car for almost a year without the car being run though before the oil was drained and the engine sent for the rebuild. Sure I read somewhere that the oil can damage the diaphragm in the sender but not 100% sure.

QBee

18,765 posts

121 months

Saturday 14th May
quotequote all
If yours is the same as mine (99 car) the sender has a single wire , the earthing is via where it is screwed into the block.
I have no idea why a bad earth should cause a false high reading, but my first thought is to earth the body of the sender to the block separately.

kris450

Original Poster:

518 posts

171 months

Saturday 14th May
quotequote all
QBee said:
If yours is the same as mine (99 car) the sender has a single wire , the earthing is via where it is screwed into the block.
I have no idea why a bad earth should cause a false high reading, but my first thought is to earth the body of the sender to the block separately.
Doh ! Stupid me, I should have mentioned it isn't the original sender. Its one of the Isspro senders with the 2 terminals, one to the gauge and the other a ground/earth.

It was working perfectly before the strip down (even if that was a while ago) which is why I'm hoping it just needs replacing. Just trying to see if anyone has some other obvious ideas I'm missing.

Zener

18,368 posts

198 months

Monday 16th May
quotequote all
Get a mechanical set on the motor and finish breaking in the cam whislt moitoring OP I doubt you have an OP issue frankly , a cheap kit like this will confirm and useful for the tool box anyways , for example Ebay item number 265679304198

kris450

Original Poster:

518 posts

171 months

Monday 16th May
quotequote all
Zener said:
Get a mechanical set on the motor and finish breaking in the cam whislt moitoring OP I doubt you have an OP issue frankly , a cheap kit like this will confirm and useful for the tool box anyways , for example Ebay item number 265679304198
I've literally just come back in from the garage from doing this !! Pressure instantly rose to 60psi and stayed there solidly, dropping to around 55psi once the oil was up to temp. Still stunned I managed to order a gauge set on a Sunday morning and have it delivered by 9pm that evening !! Guess Amazon can have its uses sometimes.

Massive relief !

New sender has been ordered thumbup

QBee

18,765 posts

121 months

Monday 16th May
quotequote all
Note to others thinking WTF.

In my experience the TVR gauges and standard senders often read low.
My car has always sat at around 35 psi at start up and slightly lower on a lengthy drive. I suspect the truth is 10-30 psi higher.
The reason it doesn't bother me, after 47,000 miles and more than one engine, is that this has always been the case and what the gauge does is warn me if the pressure is abnormal. For example, on leaving Snetterton after an enjoyable track day (max speed 135 mph) I noticed I had NO oil pressure whatsoever, yet the warning light wasn't on.
My TVR guru had been on the same track day, and he stopped in my A11 layby on getting my panic phone call ( I had over 100 miles to drive home) and confirmed it was simply a loose wire on the sender.

Sir Paolo

215 posts

45 months

Monday 16th May
quotequote all
Hi all, as a rule of thumb, the standard oil pressure relief valves are normally set to open at 45 psi.

So, you shouldn’t really be seeing much more than this on the gauge - but we all know the sender and gauges aren’t known for their accuracy.

Wolvesboy

567 posts

118 months

Wednesday 18th May
quotequote all
I just changed my oil pressure sensor and the new one had two connectors.
Having run a new ground wire etc and started it up, the gauge shot straight to the max and stayed there! I was sure that I had got the wires the correct way around (I had) and swapped them to see if it made a difference. It did and the gauge now works fine! Typical!
It may be the simple case of the two wires being placed on the wrong connector.

Steve_D

13,549 posts

235 months

Wednesday 18th May
quotequote all
I've mentioned on another similar post that there are 2 versions of two pin/terminal senders.
one is signal and earth with the body isolated.
The second is a dual function sender. The body is earth. one pin is a resistance for the gauge the other pin is a switch for the oil warning lamp.

If the sender you have is the first type then it should make no difference which way round the wires are connected as it is just reading a resistance.
If it is the second type then one pin will produce a resistance to earth via the body the other pin would produce a direct connection to earth and produce your endstop reading.

Steve

kris450

Original Poster:

518 posts

171 months

Wednesday 18th May
quotequote all
I'm pretty sure its a short somewhere in the wiring annoyingly.

Its definitely not a post for a warning lamp or a second gauge, its purely an earth. Tried swapping wires around, running with just one wire on either terminal with the sender earthing through the block. Still same results.

Last thing I want to do is now unwrap all the loom to look for the issue madbiglaugh

ric355

212 posts

126 months

Wednesday 18th May
quotequote all
kris450 said:
I'm pretty sure its a short somewhere in the wiring annoyingly.

Its definitely not a post for a warning lamp or a second gauge, its purely an earth. Tried swapping wires around, running with just one wire on either terminal with the sender earthing through the block. Still same results.

Last thing I want to do is now unwrap all the loom to look for the issue madbiglaugh
I did some testing on my 2000 model oil pressure gauge a few years ago. It's a 0-250ohm gauge where the readings are as follows:

200 ohms = 15psi
100 ohms = half way between 45and 60 = approx 52psi
50 ohms = 2/3 of way between 60 and 90 psi = just over 80psi.
0 ohms = full deflection (past 90psi).

That works out at approximately 2.3 ohms per psi. I didn't try to establish exactly what 90psi was but it projects to about 40 ohms.

The sender is typically a 33-325ohm sender with max of 150psi, and this is where the mismatch comes from. i.e. the if 325 ohms is 0psi and 33ohms is 150psi, then thats (325-33)/150 = 1.94 ohms per psi. If your sender has a different spec this you can plug in the numbers to verify what the gauge should read at a given PSI.

For example a psi reading of 51 from the original sender is going to be about 100ohms, which is going to show approximately 43psi on the gauge.

To test your loom, get some resistors in this range and put them across the end of the wires you would normally have attached to the sender. Worth doing this before you strip it down.

As you can see, original gauge and sender aren't all that far apart really, and it was certainly enough for TVR to just let it go, being what they were at the time. By the time the sender is reading 62psi the gauge would be showing 52psi.

Zener

18,368 posts

198 months

Wednesday 18th May
quotequote all
Have mentioned it before was a guy on here selling gen Smith's sender's that worked great but got fed up selling them to numb-nuts/whingers shame really , 6 years on still working as is should fitted 2 others different cars same story

kris450

Original Poster:

518 posts

171 months

So to update and bring this to a close as such.

Managed to find the original tvr sender the car had when I bought it. Fitted it and everything worked correctly. Guessing I've either bought the wrong sender (almost certain on this after further research) or its a duff new one.

Happy days and glad I've found the issue.

Ps not sure if this is allowed, but if anyone is in need of an Isspro sender, R8917-03, pm me as its clearly not compatible with my later car.