draining and refilling coolant, 1978 B

[Guinn]

I would like to remove and modify the heater control valve on my 1978 B and need to drain and refill the system. What is the best way to drain the system? With no radiator cap, how does one add coolant, other than the pint or so in the recovery tank?

 

[timbomath]

Guinn, It seems the only way is to pull the lower hose off the radiator. Some people take the radiator to a shop and have a petcock put in but the hose-off idea works fine. New coolant is poured into the thermostat housing by taking the big nut (plug) off the top.
Cheers,
Tim Matheis

 

[8NFord]

First, you need to fill via the large plug on top of the thermostat housing.

You have several options for draining. The best is to go ahead and pull the radiator and have a standard plug installed for future use. Another option is that you can install an adapter in the lower hose with a drain in it. Depending on the carb setup and the heater hose configuration you may be able to install a back flush style adapter in the small heater hose. It is a good idea to back flush both the engine block and the heater core.

 

[Guinn]

Thanks, Fordman. Haynes doesn't give much info on simple maintenance. Guinn

 

[Guest]

for what it's worth I never remove the bottom hose, what I do is carefully put a screwdriver between the hose and the pipe, only allowing the coolant to run out slowly, It usually runs down the handle of the crew driver and into my basin. I have found that by removing the hose I end up with more antifreeze on me and the floor than in my basin. I also have found it just as easy to remove the top hose from the thermost housing and fill thru it (consequently I am filling the rad first). When the antifreeze comes out from the thermostat housing I quit.

 

[beebopbogo]

I had a chronic overheating problem which turned out to be the cause of me not filling the coolant correctly. I unscrewed the large plug from the top of the thermostat housing and topped up the coolant that way.

The problem? The coolant wasn't going into a large part of the system. Because the engine was cold, the thermostat was closed, essentially blocking off a large part of the cooling system. My overheating was caused by a low coolant level, even though I thought it was topped off.

What I have been doing since then was to unscrew the 3 nuts and removing the thermostat housing so I could lift out the thermostat to fill the complete system. It works for completely changing the system, but you have to replace the gasket almost every time (mine keeps tearing). To just add a bit of coolant to keep it topped off, I usually just add it through the plug like before.

 

[Guinn]

Ah, I wondered about the thermostat not allowing the block to fill. Figured I would pull it like you say if I have to drain the whole thing. Seems MG wasn't too smart. The older ones had radiator fill caps, radiator and block drains. The newer B's are "improved" by eliminating these amenities?

 

[timbomath]

I drilled a 5/32" hole in the thermostat on my 79 and it seems to take care of these problems with no bad side effects.
Cheers,
Tim Matheis

 

[Guinn]

Thanks, all and keep the good ideas coming!

Guinn

 

[timbomath]

It should be added that the design of the late model cooling system fill-up works only when the motor mounts are in good condition. The filling of the engine coolant works fine when engine height is sufficient to allow coolant to flow to the radiator and fill the engine from the bottom when filling throught the thermo housing. If the motor mounts are weak or broken the hose to the rad is going uphill and makes it hard to fill the system. In my case the DPO had removed the thermo altogether (which makes it run too cool) to get around this problem. When I replaced the motor mounts it raised the engine almost 1 1/2" and makes filling the system very easy and the hole in the thermo helps avoid air in system.
Cheers,
Tim Matheis