MGF or MGTF with an overheating issue, first step is to replace the MGF coolant tank cap. It is a common point of failure and and is about the easiest potential fix available. So, if you have steam coming out of the coolant tank this is step one. Alternatively, if you are loosing coolant, but no trace of a leak, also change the cap.
Background #
Lots of info on the internet about why a car has a pressurized coolant system. Not going to repeat it here. A quick TL;DR version would be something like this. The pressure increases the boiling point of the coolant and makes the cooling system more efficient. The glycol of anti-freeze further increases the boiling point (and the freezing point). So all in all, car coolant systems work best pressurized and with a water/glycol mix as the coolant. You can also just move on to the video below.
The cap on the expansion tank of an MGF or MGTF maintains a pressure in the cooling system of 15PSI (1.03 bar). Interestingly for me, this is the same as my 1977 MGB. The later model MGBs used 15 PSI expansion tank caps compared to the earlier models which used 10 PSI caps.
As such this makes the coolant cap a critical part of the cooling system. It’s not just there to be like the cap on a jug of liquid to keep the liquid in place.
Getting A Quality Cap #
Sounds easy, but isn’t as easy as one might hope. As with many things there are sometimes supply chain problems. Parts for the MGF and MG TF are no exception. There was a batch, for example, that looked right but didn’t work. There was a small, but unique way to identify them, they were missing the dimple in the very centre of the top of the cap. Now there are also some copy caps floating around which have the dimple but are still not very good or well made.
The following video is linked to from the Discount MG Rover Spares (DMGRS) website. They have a very good reputation of supporting enthusiasts and providing quality parts. The video creation was supported in part by them.
MG Rover coolant caps: the good, the bad and the truly awful #
Conclusion #
Don’t pick a MGF Coolant Tank Cap based on price! Use a reputable supplier who will stand behind their products. Even the best suppliers sometimes will be affected by parts manufacturers doing a crappy job. It’s not possible for the suppliers to do a quality control check on every part coming into their warehouses.
DGMRS have the Febi caps mentioned in the video. I’m sure other quality options are available. Just be discerning when buying your MGF Coolant Tank Cap.
Other Materials #
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