Oil light at high revs

[crump167]

Hi all, I have a rebuilt 1.9 dg, ticks over and drives sweet but get I get an oil light at high revs, turn engine off and restart, the light goes out until I rev high again. Any ideas would be much appreciated

[marlinowner]

You don't say the year of your engine/van, it sounds like a problem with the high rpm oil pressure switch fitted to latter vans (see wiki), although this circuit should sound a warning buzzer as well as the light coming on. The switch is on the engine near the water pump. Disconnect the wire from the switch and connect it to ground. If the light still comes on then you have a bad connection somewhere between the switch and the monitoring circuit which is built into the back of the speedo. If the light stays out then you have either a duff oil pressure switch or low oil pressure.

[crump167]

Cheers for that, engine is a mixture of early and late parts , the high pressure switch was disconnected when I got the van, the wire is just cut off at the connector block and just hanging, only the low pressure switch is connected.

[kevtherev]

Oil light at high rpm would suggest an oil pump fault.
Was the pump primed after the rebuild?

[ghost123uk]

In view of you just using the single low pressure switch, your symptoms are most odd. Likely electrical but I would get the pressure checked at a service garage asap.

Clutching at straws, but how much oil did it take when you filled it up? My thinking is with the engine being a "bitsa" you may have the wrong dipstick or tube fitted and your oil level might be low. This might cause a shortage at high revs. Not very likely though, I agree, and anyway, I think all the tubes and dipsticks are the same.

[colinthefox]

Have the two oil switches just got swapped over? The two switches operate differently. Does the oil light come on when the engine is not running? If it doesn't then the wrong kind of switch could be connected.

Try connecting the wire to the other one.

Worth a try.

[E D I T] sorry, just read your original post. Forget this lot please! [/E D I T]

[marlinowner]

High pressure circuit should be grounded if not used. Ground the wire, problem solved. Although an oil pressure gauge might be a good idea.

PS if you've got the wire and the switch, just connect them together.

[crump167]

Ok, so I wired up the high pressure switch. Turn on ignition oil light is on, start up oil light goes out, been for a drive, gave it some revs, oil light doesn't come on. Problem solved????

[kevtherev]

Yes.

[AdrianC]

Ok, so I wired up the high pressure switch. Turn on ignition oil light is on, start up oil light goes out, been for a drive, gave it some revs, oil light doesn't come on. Problem solved????

Yep, definitely.

The light control circuit expects to see different things from the two.

The low-rev switch earths the wire to bring the light on. When there's no pressure, because you haven't started the engine yet, the light is on - that's a visual test that it's working. If the wire becomes disconnected, the light will never be earthed, so the light will never come on.
The high-rev switch breaks the earth to bring the light on. If the wire is disconnected, the connection that puts the light OFF can never be made, so as soon as the engine goes over 2k rpm (the speed below which that switch is ignored), the electronics thinks there's insufficient pressure and puts the light on.

Shorting that wire would mean that the control will always think there's good pressure, even if there isn't. Wiring it to the switch means it's working as intended.

[crump167]

Many thanks all, mind at rest