Drain coolant

Wig

Used to be the case ....on cars I owned anyway.

Before draining coolant to replace it you would put the heating to the hot position run the car a few seconds ..turn it off then drain the coolant. So you have opened the valves for the heating circuit and then you drain everything otherwise you would be leaving some in the heating circuit.

Are cars still the same now or is the heating circuit always open in modern cars?

And what about cars which are electronic so there is no mechanical switch or lever for the heating, but now they are controlled from a touchscreen.

reeac

That would certainly have been the case when heating was controlled by a valve in the coolant circuit so that the coolant in the heater matrix was drained out. That design, however, was superceded way back ( in the late 1960s?) by one where there was a constant coolant flow through the heater matrix with the heating being controlled by flaps which blended heated and cold flows of air. This design means that the coolant in the heater matrix will automatically drain out along with the rest. I certainly owned a 1956 MG saloon with the former system and then a 1964 Rover which had the latter.

Wig

I'm talking about ..

1987 - 1991 VW polo
1990ish Vaux Carlton
1998 Vaux Omega Whatever year "P & R" reg were
1998 Fiat Marea
2000 Mitsu Colt
2003 Corsa

Now I'm not sure which of these the manual said to open the heating before draining the coolant but I know it was one/some/all of them.

I will check the manuals if I can find them.,.

facade

Most modern cars are so poorly designed that it isn't possible to get half of the coolant out, so the instructions now are along the lines of


Drain radiator
Fill back up
Run until hot with radiator cap off

Drain radiator


Repeat until the coolant is clean


Then add the required neat antifreeze and make up with water, although neat antifreeze is hard to find, as everyone likes to pay a fortune for water and buys ready mixed.

chrisw

The Ford Ka certainly had a troublesome heater control valve.

So that's one example where the coolant isn't always open circuit. No others spring to mind though.

gmm30

Surely the answer here is to always turn the heater to hot? At worst you've wasted 2 seconds moving some air flaps?

EdGasketTheSecond

facade wrote: »

Drain radiator
Fill back up
Run until hot with radiator cap off

Drain radiator

Repeat until the coolant is clean

Then add the required neat antifreeze and make up with water, although neat antifreeze is hard to find, as everyone likes to pay a fortune for water and buys ready mixed.

Only adding cold fluid, water or antifreeze, to a hot radiator can crack it or at least help shorten its life.


My approach is take off bottom hose (as then there are no drain plugs to leak when you try and do them up); maybe jack up the car to get a little more fluid out. Refit bottom hose and refill with new mix; job done. I know it won't have changed much more than 50% of the fluid but that is good enough in most cases. You can always repeat at more frequent intervals if you want to.