Headlamp vacuum system

[Simon Lewis]

The headlights on my Elan S4 are playing up. They will rise, if activated, when the engine is first fired up and then stay up even when the engine is hot. However, if I attempt to raise them after I have been driving for a while, they will only partially rise and very slowly. Does anyone have any ideas what might be causing this? If there was a leak on the vacuum system, I assume it wouldn?t make any difference whether the engine was hot or cold? Could it be a faulty non-return valve? Any suggestions would be much appreciated. I have a non-failsafe system installed.

[Gray]

A faulty non-return valve won't normally prevent the headlamps rising, although they might droop under high throttle low vacuum conditions and drop when the engine is stopped. It sounds like a leak, but why it is worse at times is not clear. Connect one item at a time to test if there is no obvious cause of the leak. Hopefully its not the chassis cross-member.

[jimj]

The vacuum is created when the you are decelerating and a leak, or faulty valve, would normally be obvious with the headlights drooping when driving up, say, a long hill. The fact that yours works when cold but not when hot would suggest that some pliable part like the rubber hose deforms when hot. You just have to check all the joints and the T piece on the chassis cross member. It could even be the switch itself being warmed by the heater, you can check this by pulling off the two pipes from the switch. With the engine ticking over just block the end of the pipes with your fingers.
Jim

[Simon Lewis]

Many thanks for your helpful comments. I?ll investigate further.