Heater problem

[r4_rick]

Not my problem yet, but it could be if I buy the car !
Speaking to a guy who has a valver for sale, says that when the car is on a long stretch of road and the engine is warm up he cannot get any hot air out of the heater (but he can when its running around town) ?  I know this is a very vague description, but any ideas on what the problem is and what it would cost to fix.  He has flushed out the system suspecting an airlock, but that has not solved the problem.

Any help appreciated
Rick

[Gambit]

if he flushed the system out properly, i.e. with the heater set to max heat and squeezing the pipes to get an airlocks out then i would look at changing the bypass valves

[r4_rick]

thanks Gambit, is that an expensive job ?

[thedentist55]

After youve carried out Gambits suggestion:

Does the temp guage go to the middle (normal running temperature, between hot and cold) when running on a long stretch?

My first suspicion in this case is that the thermostat is staying open, meaning that the coolant temp only gets up during stops in traffic when cold air is not passing through the radiator. If not check for signs of blown head gasket before buying.

[rubjonny]

Sounds like either the matrix is blocked and/or the bypass valves are shafted.

[Chris Green]

how big a job is it to replace the heater bypass valves?

[rubjonny]

Dead easy, don't even have to drain much coolant as its at the top of the cooling system.  If I were you I'd just bin em altogether, and whilst you have em off give the matrix a good flush through with a hosepipe

[Chris Green]

are they expensive to replace though? I'd rather replace them than remove them if I've got the choice.

What do they look like?

Cheers!

Chris.

[rubjonny]

Not too expensive, I think they were about ?30 when I bought some new ones from VW.  They arn't available at the moment though, apparently more stock is arriving later in the year.

The valves are fitted inline with the coolant feed & return hoses to the heater matrix, one is metal the other is plastic and they are joined with a small rubber tube.  You can't miss em