Originally Posted by Orville
When you switch the ignition on, you should get the buzzer sounding and the water and oil alarm lights etc..
There were some changes to the ECU and warning sensors on the DT range of engines in the nineties, especially the overheat sensors(three different types). Not all of them sound the buzzer when you switch on.
As well as the temp and low oil warning sensors, there is an oil flow sensor/filter in the oil supply line, on the lower port side of the engine. If flow is reduced, the revs are cut. Disconnect the sender, undo the four screws and you'll find a small filter which is probably clogged up. Clean it carefully because if you damage it, you can't buy just the filter. You have to buy the complete sensor unit at a cost of about £40. Refit the unit and just to the right of the unit, you'll find a small bleed screw for the oil system. Bleed the system, preferably running the engine on a 50-1 premix.
Then, open up your control box and put 12volts into your warning horn to ensure it's working. If you don't want to open up the control box, lower the level in the oil tank and this should set the warning horn off.
If all that fails, run the engine up, open the throttle and disconnect the oil level, oil flow and overheat sensors one by one. If the revs pick up, you've got a faulty sensor.
While you're doing all this, it's not a bad idea to drain the oil tank and clean it. Condensation can cause small lumps of jellified oil to collect around the in- tank filter
If all that fails, you're buggered.