Heater not getting hot

#1
just bought my first 1972 p6 3500 auto drove 85 miles home engine temp gauge stayed in the green.
Heater would Not getting hot (cold all the way home) opened bonnet top & bottom rad hoses are hot. Heater hoses going into heater box just look warm. Is there a heater valve somewhere on the engine.
Any help would be appreciated.
Regards Ray.
 

harveyp6

Well-Known Member
#2
Make sure the the heater control levers are actually operating the flaps. There isn't a heater valve on a UK spec car. You could try an 88 degree thermostat, but probably the heater matrix is blocked or the seals on the heater flaps have failed.
 
#3
Make sure the the heater control levers are actually operating the flaps. There isn't a heater valve on a UK spec car. You could try an 88 degree thermostat, but probably the heater matrix is blocked or the seals on the heater flaps have failed.
Think I will have ago at back flushing the matrix first.
 

MikeMelb

Active Member
#4
When I did this job many years/decades ago I was advised to allow myself a long weekend.
What I should have done before starting (but did do afterwards) was obtain a spare heater matrix and have it reconditioned so it could be swapped over for the one in the car without having to wait for that one to be reconditioned.

Just a suggestion. Not sure how available they are.
 

Phil Robson

Well-Known Member
#5
just bought my first 1972 p6 3500 auto drove 85 miles home engine temp gauge stayed in the green.
Heater would Not getting hot (cold all the way home) opened bonnet top & bottom rad hoses are hot. Heater hoses going into heater box just look warm. Is there a heater valve somewhere on the engine.
Any help would be appreciated.
Regards Ray.
Sorry, but I have just seen this post :rolleyes: & know of a very easy fix that is quite likely to work.

I would strongly advise that you follow the instructions on the red radiator label on your car (if you have one). I didn't actually read mine for about 10 years, but it makes the difference between your heater working like warm breathing to a decent fan heater in around 30 seconds flat and of course helps the engine cooling into the bargain!

s-l1600.jpg

Obviously be careful with the hot water, but undo the radiator cap when the engine is just warm enough to idle smoothly & rev the engine a little which can be done from the throttle lever on the n/s of the engine. You'll see just how far & fast the coolant level drops. Once filled (& cap replaced whilst the revs are up), there is much less air in the system which presumably otherwise tends to collect in the heater matrix.

I've recently replaced Hazel's poor radiator with a good one & have done this very thing this morning. The difference to the heater's output is truly amazing.

You should be able to enjoy a drive out even in winter :cool:
 
Last edited:

MikeMelb

Active Member
#7
Don't forget a pressure test before assembly (not casting any aspersions on the source of the part, of whom I have no knowledge, but my experience with recond radiators is it is a worthwhile precaution)
 
Top