A Conundrum?????

[COLVERT]

Originally Posted by mss

This is a long shot.

The additional load placed on the engine when the aircon is drawing power will lead to a larger vacuum in the inlet manifold. Could it be that as a result of this larger vacuum, a small amount of coolant is being sucked in past a marginally sealing IMG?

Wouldn't you get a larger vacuum by simply driving faster ??

[MSS]

Originally Posted by COLVERT

Wouldn't you get a larger vacuum by simply driving faster ??

I would say not necessarily, because the IM vacuum is dependent not ojust on the engine RPM but also the throttle opening. This is why in the old days when we used to employ vacuum gauges to diagnose engine problems, inlet manifold leaks had far more effect on the engine at idle than at high speed.

[COLVERT]

Your post actually said the vacuum would increase with the air-con putting an additional load on the engine.

I meant that an increase in speed would also put an additional load on the engine too.----

I was following your reasoning.--

[MSS]

Are you ignoring the effect of a gearbox?

I did say that my proposition was a long shot.

What proposition are you tabling to explain the OP's obsrevation?

[Mike Noc]

Originally Posted by mss

This is a long shot.

The additional load placed on the engine when the aircon is drawing power will lead to a larger vacuum in the inlet manifold. Could it be that as a result of this larger vacuum, a small amount of coolant is being sucked in past a marginally sealing IMG?

The OP's car is a diesel - there is no vacuum in the inlet manifold.

[MSS]

Originally Posted by Mike Noc

The OP's car is a diesel - there is no vacuum in the inlet manifold.

Excellent - for some reason I thought it was a 1.8k!

[robdrinkwater]

Originally Posted by mss

This is a long shot.

The additional load placed on the engine when the aircon is drawing power will lead to a larger vacuum in the inlet manifold. Could it be that as a result of this larger vacuum, a small amount of coolant is being sucked in past a marginally sealing IMG?

In actual fact the vacuum at the manifold will be lower as the bypass system will effectively open the throttle slightly to keep the idle correct during the extra load from the air con.

This means you'll have slightly less vacuum.

As regards the OP, the extra load ontberngine, coupled with the extra head at the condenser in front of the main radiator, means lots more heat, which will need to be dissipated, with this in mind, the engine will I evitably get hitter,cleaning more chance of steam coming from the expansion cap. Where are you topping the expansion tank up to, remember, it only just needs to cover the webbing at the bottom of the tank, any more that that and when the coolant expands, it's simply going to blow past the expansion cap.

[Mike Noc]

Hi Rob are you still running your diesel wth all those extra horses under the bonnet, and if so have you found any weak spots where anything has worn out or broken?