This time Roger said:
>
> Bzzzt! Wade is correct- only early B's (63-67) Have a mechanical oil guage.
> The 68 and up have a oil line going to an electrical sending unit, which is
> mounted on the fire wall near the heater. The 68-71 sender is highly prone
> to failure, and are expensive. (ie: Vicky brit- 149.00 !)
>
> 72-80 used a much cheaper switch- (10.95), which may not be compatible with
> the 68-71 guage. Scott?
>
> Or, the guage for the 72-76 may fit the 68-71- I'm not sure tho.
Bzzzt yourself. :>
72 onward (or maybe late 71) had a mechanical oil pressure gauge. The earlier
cars (68-71) had the sender mounted to the block over the oil filter, with
a short braided hose looping over the distributor to the oil galley fitting.
On the later cars, the oil hose goes from the block up to a brass coupling
on the fire wall. in this coupling is a oil pressure *switch*, and off of
the back of the coupling is a hard line that disappears into the passenger
compartment which goes to the mechanical gauge.
In '72, MG's gained what was known as an "anti run on" valve. This electric
valve was hooked in to manifold vacuum and the charcoal canister. Power was
supplied to this valve only when the ignition was off. The ground for this
valve was supplied by the oil pressure switch mounted on the fire wall.
This switch is backwards from normal idiot light switches. It is normally
open, and closes with pressure. Light switches do the opposite.
When the key is turned off, and oil pressure still exists, this valve opens.
When it opens, it puts manifold vacuum to the charcoal canister, which in
turn puts vacuum onto the carb bowl vents. With this high vacuum in the
float bowl (higher than in the carb throat anyway), no gas is going to flow
up and out of the jet. No gas flowing means nothing to burn, which means the
engine can't run on (diesel). Sinple and it works.... as long as all the
lines are there and intact.
Randy
randy@taylor.wyvern.com
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