No heat at low speed

Chrysler Town and Country. The engine warms up just fine regardless of my speed or throttle position, but the cabin heater has started blowing cold air when I back off or sit at idle.

It may be relevant that we hear a lot of gurgling in the dash soon after starting the engine?

What could be causing this?

I’d say your coolant is low. When the engine is cool, take the radiator cap off (don’t do this when the engine is hot!). You should see the radiator full and some extra in the overflow reservoir. If the top of the radiator is dry, that’s your problem.

Then you need to find out why the coolant is low.

I agree with @doubleclutch since this problem is as common as dirt. I also agree with @PvtPublic because coolant does not disappear without a reason.

Thanks all. Vehicle was hot when I got these messages, so I topped up the reseviour. It seems to have worked for now. Must find the leak as you say!

Yep, the usual suspects: Hoses, water pump weep hole, reservoir itself, radiator plastic tank leak or tank connection, radiator cap if you’ve got one, etc. Look for traces of minerals.