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MG MGB Technical - 1980 MGB; How to fill radiator?

Posted 28 June 2006 at 02:17:44 UK time
D Corbett, New Jersey, USA,
Just replaced the lower radiator hose and lost all the fluid. Tried to fill but the cap is on the overflow and the fluid won't run into the radiator and cool the engine.
Tried to warm it up to see if that would pull the fluid into the radiator, but it got hot quick.
Has anyone run into this and can help me get back on the road for this beautiful driving weather?

D Corbett

Both the factory Driver's Handbook and the Workshop manual cover. The water elbow (thermostat housing) has a removable plug on the top of it. The factory solution is to fill the cooling system through the hole, then replace the plug and top up the expansion tank, as necessary. A funnel is a decided help when filling through the water elbow.

A better system is to remove the upper radiator hose at the thermostat housing, fill the radiator and block until you just see water at the thermostat housing, reconnect the radiator hose and finish filling through the hole in the top of the thermostat housing.

Robert Bentley Publishing produces a copy of the factory workshop manual which includes the Driver's Handbook. You will find that you will need both over the years and it is an inexpensive investment.

Les Bengtson

Wow! That was fast. Thanks Les. Unfortunately it's 10 pm here in the east or I'd go out and try that right now. I appreciate the tip and will try to find those manuals you recommended.

D. Corbett

Doug. Was somewhat busy myself when making the post. My dinner coming together (alone tonight), dogs to feed and medicate and still things that need to be cleaned up after my daughter's wedding using wedding cars sevenoaks last Saturday. Almost caught up.

Manuals are a good thing. The Bentley manuals are a reproduction of the factory manuals. The Haynes manuals are produced from the factory manuals and may provide information the factory does not or a way of doing things that is more appropriate to the hobbyist. I am not overly impressed with the Chilton or Clymer manuals, but the AutoBook series (I believe this is the name, Kenneth Ball was the author) seemed very good when I was starting out many years ago. I have been trying to find a good, used copy for both the MGB and MGA for some time. Time spent in used book stores is always an adventure.

Lindsay Porters mgb restoration Manual (several slight variations on this name over the years) is a good resource as is Jim Tyler's "MGB Owner's Survival Manual".

This BBS is one of the best resources available, but is best used to supplement the written sources rather than replace them. The written sources, including the Moss catalog, provide us with a common frame of reference to work from.

Should take you about 15 minutes to fill the car's cooling system up. Fill the expansion tank about half full, take it for a good drive and enjoy it. The following day, check the level of the fluid in the expansion tank as any excess air should have been evacuated from the system when your engine was up to operating temperature and would be replaced by the fluid in the expansion tank. Thus, not unusual to find the tank low when rechecked after a coolant change. You only need to worry if the tank keeps getting low.

Enjoy. Les
Les Bengtson

The method of taking the upper hose loose and filling it quickly is a good idea, however, you must bleed all of the air out of the system. It is imperative that is done and the only real way that I have found to do this is by partially filling the header tank. Open the heater valve to allow that fluid thru the system,
Leaving the filler cap off of the header tank, remove the cap on the thermostat housing. Newer thermostats do not come with a 1/8th hole in it so that is necessary too to get the air out. (drill one on the flat of the housing as necessary to allow bypass of the air, otherwise the air will be blocked unless the thermostat is partially open and being cold, it will not be.) I install a funnel that will fit snugly into the hole of the housing. I top it up until it gurgles down, I let that settle and keep filling until the coolant starts to top off. Every time I fill, I squeeze the bottom radiator hose to force the air thru the system, I keep doing this until the coolant level is nearly level at the bottom of the filler hole on the thermostat housing. Once it is nearly full you will notice that the header tank is nearly full, at this point install the cap there and then continue as previously noted until no more bubbles appear out of the funnel.

The system will not self bleed and it will cause hot spots that will lead to cracking of the head.

Good luck,

The plug in the thermostat housing is plastic as standard, but a much better brass one was available as a spare part. The plasic one is easy to mess up and the brass one looks much nicer. I fitted one about 20 years ago so I have no idea where to get one now, but the mg specialists ought to be able to help.

John Prewer

John beat me to it, but I second getting the brass plug. The stock plastic one get pretty chewed up over the years. And like him, I can't remember where i got mine either.


I found on mine I could get all the air out but having the header tank half full then filling the radiator through the thermostat housing. Then, with the plug in place, I would squeeze the top hose several times. As the highest point that's where the air bubbles rise to. You'll hear the air being forced out into the header tank and coolant being sucked back in once you release the hose. Do that a few times and you should be able to feel when all the air is gone.

I am sure I got that tip from someone off here a while ago. All I need to do now is stop the small leak around where my aftermarket thermostat bulb capillary goes between the hose and radiator inlet!

Simon Jansen

A 3/4 inch pipe tread will work fine with pipe tape to seal it. Any plumping dept should carry this.

This thread was discussed between 28/06/2006 and 29/06/2006

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