Club 80-90 Forums

My petrol Webasto HL32 suffers with a vibrating exhaust when starting up and running.
What causes this?
Without the silencer, the howl from the combustion chamber is very loud.
The heater is mounted on its side under the van in a box.

I think that maybe the burner can produce a resonating flame.
Which is amplified by the exhaust pipe.

About 1 in 50 chance of this happening - doesn't seem to happen if heater is hot from a previous run. I have not pinned it down as to the cause but have thought about an air leak at the exhaust outlet stub as I test them them without clamping tight. In my experience it soon stops as it warms up so it may be the tolerance of the gaps between the various metal components inside the heat exchanger. It can happen with any model of heater not just the Air Top 32, diesel or petrol.

Interesting.
Yes the howl decreases with time.
I was thinking it might be temp related or more mixture related.
As on start up the pump is working hard and the air flow is low.
So Im assuming the flame is bigger, less stable and this causes the pulse jet type noise.
Then as the fan speed picks up it takes on a better mixture ratio and the flame stablises, as the residual fuel burns off the howl decreases to a low drone.
This drone must be the flame ignighting new vapourised fuel.
What are your thoughts on that theory?

It could be anything. I have even thought about the air passing over the end of the burner tube. ( possibly create a sawtooth edge to the end of the tube to change the airflow a little ). Trouble is that I have not been able to reproduce it on demand to investigate it more.