Oil pressure sender (again)

[PetrolHeadPete]

Decided it was time to stop messing about with my old BMI branded oil pressure sender. Lost trust in it! (I fixed it after it leaked and never quite believed in it again)

Sad to say it became a bit of a mission to find an alternative to the rather pricey versions from various TVR specialists.

Well, I think Ive done it. Its basically a VDO type 0-5bar 10-180ohms 1/8th NPT thread. You can use pretty well any of the variants (some have a separate ground terminal, some have a terminal for a dedicated warning lamp switch and some have both (making 3 terminals!)). Just search on "oil pressure sender 0-5bar" and you'll find lots.

There are various genuine VDO units at about £40 delivered...or...on ebay £16 delivered for an aftermarket unit of dubious lineagae. That's what I went for and it works! Just fitted it and give it a quick test. Seems to read about right but its all a bit hard to tell (getting 45psi at cold idle on 15W50 oil). Need to do a proper hot run soon.

I know a couple of folks had tried to find an alternative to the "TVR" unit...well...here it is

[ochten]

I bought the same cheaper (Ebay is full of it) item. But if I compared the values with a hot engine, the VDO is 30% lower than the original. Hot idle is very low with the VDO. Perhaps to do with the shape/seize of the diaphragm?

[PetrolHeadPete]

Are you sure you got the 0-5 unit not the 0-10?

[ochten]

yes, I think so. It has a marking on the connection 0 till 10 bar
Is that the trick?

[ochten]

I made a quick test on Ebay co uk and Ebay de (Germany) The VDO items 1/8 NPT 5 bar are not cheaper than the original TVR items seems to be.
Somebody working for the VDO Company that we can make a groupbuy?

[PetrolHeadPete]

Ah, needs to be 0-5bar. This is 80psi. The 10 bar unit outputs the same max resistance but at 160psi.

Have a look at this one.

http://cgi.ebay.co.uk/Oil-Pressure-5-bar-Sender-Un...

This is the one I got. Will report on hot reading tomorrow if it stops raining!

[ochten]

and is it still raining?

[PetrolHeadPete]

It was dry for long enough to give it a blast.

Conclusion, close but not quite right. It seems to read a bit high.

Cold Idle on 15W50: 45
Hot Idle: 20
Hot 6Krpm: 70

With a quick bit of measurement the dash seems to show 45psi when the sender is outputting 81ohms.
I think I've concluded that strapping a 390R resistor in parallel with this sender will bring it closer to correct (whatever that means). It makes the sender slightly non-linear but pretty close to what the implied TVR scaling was.

Also concluded that the old BMI sender had a non-standard range. Can't find any data on it all, seems that bmi went out of business ages ago and there are no cross refs to that unit

[PetrolHeadPete]

Soldered a 390 ohm resistor from contact to the body of the sender near the terminals. Lovely job ! Now reads 15psi hot idle, around 40+ from 1500 to 2K rpm, and just over 50psi at 6K+. Much happier that this is "close" now having pre-checked the new sender at 5bar (air) just to check the full scale was correct (it was spot on).