They alert you when your coolant level drops below half way in the header tank giving advance warning of leaks, which with a modular engine like the MGFs can result in major damage.

I'll leave a jug of antifreeze ... in Lambton Co. since 2011. ... I found the jiggle valves work really well to get air out of the system....

In some cooling systems that jiggler is to let air out so it pressure doesn't slow the coolant going in. It's been a long time since I worked on a later model B but would it help to leave the housing plug off until the coolant gets to that level ...

Since I replaced these hoses going to/from the heater matrix, I have read on different forums of 3 or 4 more people that have found one of these hoses has failed on their F. I'm putting together an article on replacing coolant hoses for an upcoming issue of NAMGBR's MG Driver.

Not in the flat portion anyway. Unless it's hidden under the spring. Allan, This "tadpole" you are referring to. Is this like a small "tee" shaped piece that kind of wobbles around in a slot? It kind of acts like a check valve. So air can flow up but coolant can't flow down?

I'm wanting to adjust the valves this evening and I'm not finding the proper procedure. I have the MG Workshop manual that supposedly covers M type thru the TF 1500 put the procedure is not clear as if it applies to the TF. It mentions the TA, TB, TC and TD (as one procedure) but not the TF. It als

Hi there... I'm finishing off little things all over the engine this week.... I am wondering what this valve actually does? Can it be replaced with another configuration? Bipassed completely with just a hose from the crank case breather to the manifold?

In race engines, this gets plugged to assure that all the coolant goes through the rad.

My 71B is set up with a blanking cap on the radiator and a pressure cap on the coolant recovery tank, similar to that shown in the attached photo. I have a 195° thermostat with a "jiggle" hole. I have been draining the coolant through a petcock on the bottom of the radiator, then refilling by slowly pouring coolant back into the radiator. The heater valve is open.

It's quite normal. The coolant expands as it gets warm and is pushed out of the overflow. When the engine cools the water level appears to be low so the tendency is to top it up but it will just push the excess out again.

April 14, 2025 - This valve is designed as a "pull ... pull to close". This valve opens and closes very easily and should allow much better coolant flow through the heater core since the opening is more than twice as big....

In reply to # 2826595 by rntanner The choke needs two (2) hoses, because you have to have flow of hot water from the engine's coolant. One hose connected to the choke, will never get any heat, because the water would be stagnant. One hose bringing in hot water.

The only logic I can think of is, if the lever arm were at 90 deg, as the valve is only a friction fit, vibration could cause it to drop to point down and, therefore, open the valve. If down is closed, this cannot happen. Rowan. ... In the European market, MGB stopped fitting radiators with drain cocks in 1967. Draining the coolant was by disconnecting the bottom hose - not a pleasant job!

April 2, 2006 - Library Article: How to make the heater valve flow more, and thereby increase cockpit output on cool days, and plans for fabricating a high-flow "manu...

I remember seeing an old post on this forum, and for the life of me can't find it again, where there was a discussion on the lack of oil flow to the cooler. A very wise person pointed out to check the one way valves on the oil filter housing where he pointed out that if the outer valve has blown ou

The OE Moss heater control, with rubber diaphragms would impede or get blocked by debris, but this valve is almost 1/2", so I'm assuming this (REVERSE FLUSH - Locally not all Rad shops do reverse - at least that what my phone calls revealed) commercial work will really clean my system. Probably the last time this car would ever get it. ------- I'm assuming this plug showing between dizzy and Vac is coolant drain plug.

June 4, 2023 - In late models MGB, both radiator AND coolant reservoir are pressurized (hence the brass reservoir to take the pressure and the absence of a radiator cap on the radiator) The radiator cap is what allows the excess coolant to come back into the radiator from the reservoir. After engine shuts down and coolant contracts, the cap has a return valve (vacuum operated) that will allow coolant (or air, if there is no coolant reservoir) to flow back into the radiator.

Thermostat is closed, coolant in engine builds up heat, thermostat reaches operating temperature, opens to release hot coolant (is that an oxymoron???) into radiator, cooled coolant (there, that's better...) is drawn into the water pump and distributed throughout the engine...

July 11, 2026 - MG MGB and MGB GT Technical Talk