Posted on 9th September 2024

Cooling issues on the MG TF

My MG has been overheating - it's got to be the head gasket... or has it?

It was all going so well. The car was prepped with an overnight bag strapped to the luggage rack. This brought back fond memories of adventures we had many years ago in my old MG Midget, particularly since the luggage rack is something from those days I've kept all this time, and it still fits the TF well today.

We headed off on the A11 with the roof down, ready for another adventure. It was to be the longest journey we'd done in the car since I bought it, but fate had other ideas...

20 miles down the road the car started to overheat. Quickly pulling over in a safe place, I checked for leaks and let it cool down. I even replaced the expansion tank cap again (having had a garage diagnose the old one as failed). But the overheating came back straight away. A couple of hours later a breakdown mechanic arrived. He carried out a couple of tests and eventually his diagnosis was the dreaded cylinder head gasket failure: It was 'game over' for the car (for now) and he towed us home.

We fortunately had enough time to stay at home that night and recommence our journey in our other car the next day, meaning we could thankfully still make it to our friend's wedding on time!

Some days later I had a discussion with the garage that previously diagnosed a failed expansion tank cap and in the end they refunded the cost of whatever diagnostics they performed. We left things on reasonable terms. However it would later transpire that both the garage and the breakdown mechanic had missed an entirely different (and easily fixable) fault...

I decided that a 2004 MG TF is niche enough it would be wise to use someone who knows them well in future, especially if the head gasket needed replacing. After a few weeks of the car being abandoned on the driveway, a man called Russell arrived early on a Monday morning. He runs 'MG Rover Solutions', and is a mobile mechanic that travels the country, specialising in these cars. He came prepared to do the head gasket, cam belt and water pump.

Russell asked about the symptoms when the car overheated and quickly got to work carrying out his own diagnostics. Within minutes he had found a clear problem with the cooling system and fixed it. The section of the circuit that is responsible for passively bleeding air from the coolant was blocked:

Apparently a 'restrictor' in these narrow cooling pipes can become dislodged, blocking the flow of coolant causing significant air pockets to build up. I had even noticed myself that the flow of coolant back into the expansion tank from this part of the circuit was pretty much non-existent. While I thought this was strange, I hadn't quite built up enough knowledge of the car to have the confidence to try and do anything about it.

It took him less than an hour to find the fault, fix it and bleed the coolant through. So the next question was - had the head gasket failed at all? As far as he could tell all signs pointed towards 'no'!

Russell suggested that he come back in a week or two to replace the cam belt and water pump once I had time to give the car a few test drives and determine if there was any underlying problem. If there was, the cylinder head would have to come off and the gasket would need to be replaced. But he didn't want to take it off (and have to charge me for the extra work) if it wasn't necessary. I was happy with this approach, particularly given there is evidence of a recent head gasket replacement from the paperwork on the car.

As luck would have it, the refund from the original garage covered most of the cost of Russell's travel, his expert diagnosis of the cooling problem, and fixing it. He also spotted another (more minor) issue with a faulty fan switch but fortunately the ECU in these cars compensates by running the fan pretty much constantly, so that can wait.

In a couple of weeks I should know if the head gasket is holding up and the car will have a new cam belt too, hopefully restoring its reliability and giving me confidence in it again. If only this fault could have been spotted earlier. As it stands I just have to hope my own vigilence in checking the car's temperature and coolant levels has been enough to keep it from causing any more serious problems.

I take comfort from the fact that in the past I have noticed cars overheating early before and managed to avoid them running too low on coolant. I've been fortunate enough never to run them till the temperature gauge hits the red line, the TF included. In these circumstances in the past no significant damage was done.

So the question now is - can an MG Rover 'K Series' engine really survive mild overheating, avoiding the issue it is most notorious for: head gasket failure?

I'll report back soon with the outcome...