In the process of trying to figure out why I get quite a bit of residue under my oil filler cap (and in the entire PCV system) in winter only, I've done some testing on the breather heater and it works fine if I jump the Breather Heater relay.

Finally it's been cold enough to check and see if the relay is closing as it should in cold temps. It is not. I'm assuming the Ambient Air Temperature Sensor, which provides ignition 12v+ to energize the Breather Heater relay, which powers the Breather Heater element and the Windshield Washer & Headlamp Washer heater elements.

Does anyone know where this temperature sensor is?

For the winter, I'm thinking about jumping the relay with an ignition 12V+ source to see if that helps with the residue buildup.

 

Hi Nick,

The residue on the oil filler cap is normal on an XJ40, though it does seem possible that you may be getting more than usual if your breather heater is inoperative.

IIRC, the ambient air temperature sensor is mounted in the front air dam/valance below the grill and off to one side (I can't remember if it's right or left of center). On our '93 it's a small cylindrical probe with a rounded end that mounts with a small bracket.

Please keep us informed.

Cheers,

Don

 

Thanks Don,

I think I remember seeing an air temp sensor in one of the brake cooling ducts, but that could've been on my X300.

As a temporary "hack", I've jumpered accessory switched 12V+ to the Breather Heater relay by way of the white/gray wire in the yellow Ride Leveling System connector, which was the closest place I could find a suitable source of accessory switched 12V+ in the 35 degree wind outside.

I'm going to monitor the buildup and see if there are changes vs. last year:




Thanks again, Don. Next time the weather gets a bit warmer, I'll go digging for that sensor and probably just bypass it. I can't imagine the various heating elements would be too prone to burning out.

Nick