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MG MGB Technical - Oil Pressure sending unit

Ok, I can't find the answer in the archives, so I'm hoping someone can assist.

1969 mgb GT

Looks like a bad sending unit. Is there a replacement I can use? Auto parts stores show a bunch- anyone have a part number that works?

thanks,
Don
don g

It looks physically the same as one I had on a Toyota Celica, but I have no idea if they have the same characteristics. I can see why you might want an alternative to Moss at $125!
Paul Hunt

Don,

You might want to check with Tony Barnhill at his website which is theautoist.com. He has a very large collection of used mg parts.

Cheers - Dennis
D L Rainey

Thanks- I'm hoping someone knows of a modern one that will fit- I see them online for under $10. I may be going to the junk yard this weekend...
don g

Don,

Have a look at rockauto.com they have it for less than $7.

Cheers,

Jean
Jean Guy Catford

thanks, Jean, i'll do that!
i finally got time to have a closer look tonight- yikes, the hose was kinked! somewhere along the line i mis-routed it around the distributor. I now show oil pressure- hope that was it!
i'll still look at Jean's site. thanks for the replies!
-Don
don g

Don
Sounds like you found your problem. You do need to get the correct one when replacing it. Not only correct size and thread but the sender must have the correct degree of throw. The square oil gague in your car has something like a 60 degree swing so you need to match that, most aftermarket don't match that. One you can use is the Sun or Sunpro CP7577. It is a little slower to rise than the original and I have already had one fail on me but at about $19 it's a bargain compared to the moss price. Fits like original. Hope this helps.
Mike
MK Mike K

thanks, mike. the rockauto one is about 15.00 with shipping, stated for my year- better than the big unit for 10 times that much!
don g

My understanding is that the reason the real part is so expensive is that it contains an integral voltage regulator, similar to the one under the dash for the other instruments. The ones you get over the counter don't. That's not to say you couldn't find something that would work. After replacing several failed senders in my '69, I gave up and installed a mechanical gauge from a '72....
Rob Edwards

"the reason the real part is so expensive is that it contains an integral voltage regulator"

It does indeed. The first year they were provided they were powered (on the schematics at least) from the instrument voltage regulator that powers the fuel and electric temp gauges. For the next year they were powered from the full fused ignition supply, but neither gauge nor sender changed, so either it was wired wrongly or just incorrect on the schemetics. I'm not sure about them being so expensive because they contain a voltage regulator, my Celica was the same type. Then again I don't know how much a Celica one is, but given the prices of other types above even with a stabiliser like the main one you can only be talking $20 or $30.
Paul Hunt

Don, Now is the time to replace that hose. You don't want to see the oil pressure gauge falling like a rock while driving on the highway. Mine did and I was just able to shut the engine off before loosing all of my oil. RAY
rjm RAY

the saga continues. my gauge started working after un-kinking the hose, but only works for a few minutes. i bet the hose is collapsing. i bought an electric switch from advance auto for about $9, but from the prev 2 posts it sounds like it wont work (it's a part listed for a 72 B). so does the power go to the gauge, or through the sensor?
don g

A '72 B has a mechanical gauge (I got the mechanical gauge I installed in my '69 from a '72). I just looked at the AA website and it looks like what you bought is a simple switch. I don't recall a '72 having one, but later models would have one that is used to control the anti-runon valve. It's the same sort of thing that would turn on or off an idiot light, but not work a gauge....

Just for the record, that switch grounds through it's body, so power would go to the light (or whatever that switch would control) and then from the light to the switch and through the switch to ground.

HTH!
Rob Edwards

Switch or sensor? A switch would be used to turn on a light when there is no oil pressure, biut this never existed in the MGB. But in either case they only have one insulated connection, the other connection is through the screw thread i.e. to ground. So both send a ground back or not according to conditions. As such 12v needs to be connected to one side of the lamp or gauge, and the other side of the lamp or gauge should be connected to the switch or sensor. According to the Leyland Parts catalogue there is only one electric oil pressure transmitter i.e. sensor for all years that had them, i.e. 67 to 71. Before and after that a mechanical gauge was used with a capiliary pipe that lead all the way back to the block, i.e. no switch or sensor anyway. Where a switch *was* used in the MGB oil system it was to power the anti-runon valve, but that was for the 73 model year, not the 72. It will be no use where a problems with a gauge are the issue.

Have you considered changing your electric oil gauge (and transmitter) for the 72 and later mechanical one? The shape and size *looks* like it might be the same or very similar from Clausager.
Paul Hunt

>The shape and size *looks* like it might be the same

'72 is identical in appearance to '69. Can't vouch for other years. I'm also speaking only of the N.A. market -- home market might well be different.
Rob Edwards

Home market didn't use electric oil gauge at all, it used the dual gauge right up until the final dash for the 77 model year.
Paul Hunt

I second the comment on replacing the oil hose. Mine failed at 80MPH on the freeway and I had lost 4l of oil by the time I got to a safe stopping spot.

Rich
Rich McKIe

thanks for all the comments. I havent checked them in a couple days.
a new hose in on order. the sending unit is called a "switch" in the vic brit catalog, as is the cheaper, smaller one for '72-'75. as the later years had mechanical units, i dont know what these are, but i purchased one from advance auto (after returning the first one without trying it). for the price, i'll try it out.
should be able to install this weekend.

-Don
don g

Well, the $8 sending unit does not work. I did replace the hose, and checked the existing gauge with another one- both showed the same pressure, so the gauge is good. leads me back to the sending unit.

another curious thing- the pressure shows fine for about 5 minutes, then drops to 0. if i disconnect and reconnect the wire to the sending unit, the gauge goes back up. i think this is another indicator of a bad sensor.
don g

This thread was discussed between 07/10/2009 and 19/10/2009

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