Water loss worry - 2004 MGTF 1.8

Hi All

Had a coolant hose replace about three months ago (background only, may not have effected the issue).

Went on a 100 mile trip a couple of weeks ago. Before trip checked coolant, all OK. Parked up for the night, next day started car and drove about 100 metres. Coolant light came on. Stopped and checked water had dropped in expansion tank about 25mm. Topped up and continued with my day.

Check for any signs of leaks on the drive, none and water level ok.

Next day checked coolant level and drive for evidence of leaks, none. Set off on return 100 miles trip home ( motorway for 90% of the trip).

Got home water level OK. Before and after a few short journeys checked level. OK

Went for a 20 mile run on return journey coolant light comes on. Stopped and checked expansion tank water dropped by approx 25mm again!

Since then have re-bleed system and completed regular checks no sign of any loss.

Sorry about the long tale but the whole episode is a little worrying. Any advice.

Thanks

Robert

It may be nothing to worry about (ever the optimist!) I had a similar issue on my 02 TF160 this year. I couldn't see where the problem was as the temperature was rock steady. Having looked for help on this forum i diagnosed it as an expansion tank cap that needed replacing. On mine the pressure release valve was opening too early and venting vapour. When i looked very carefully around the expansion tank top there was a very faint red sheen where the coolant had vapourised when released. A new cap cost me £8 off e-bay! I've had no problems since over 3000 miles. (i had to say it didn't i?)

Norm

Seeing as the problem is not consistant, I'd be inclined to replace the filler cap first, these things aren't the most reliable component, even new ones are a bit suss. get 2 and carry one as a spare. The loss probably only occurs when the pressure overwelms the cap.

There may well be another more sinister cause for your loss, but this is a ceap and easy thing to try first.

Replaced the coolant cap as suggested by Cobber. All seems well. 40 mile trip, urban and motorway. No illuminated light and coolant settled back to original level.

But I will still keep an eye on it!

Robert

Hi Robert,
you said you had a coolant hose replaced a while ago -there may be an airlock left in the system which has moved and the space has been taken up from the tank.
Maybe worth bleeding the system from the radiator nipple ( when cold of course) just leave the rad cap of while you do it and keep an eye on the tank levels

Mike

Hi All Sorry to raise this again but I have observed the following.

I did replace the coolant cap and noted that when the coolant is cold the level in the coolant tank is mid-way on tank seam, which I understand is correct.

However, if I run the engine till the fans come on (engine bay and rad) then observe the coolant tank, the fluid has risen to approx 11/2 to 2 inches within the tank. ). The total level has increased by at least 3/4.

Is this right? or is a sign of something wrong?

Robert

Fisher wrote: Hi All Sorry to raise this again but I have observed the following.

I did replace the coolant cap and noted that when the coolant is cold the level in the coolant tank is mid-way on tank seam, which I understand is correct.

However, if I run the engine till the fans come on (engine bay and rad) then observe the coolant tank, the fluid has risen to approx 11/2 to 2 inches within the tank. ). The total level has increased by at least 3/4.

Is this right? or is a sign of something wrong?

Robert

Hi Robert,

Your coolant will expand and the level rise within the system and consequently the header tank when the system heats up and the pressure increases. In my tank the level goes from just above the middle seam of the tank to nearly an inch or so higher. If you get more of a rise than that, I would suspect you still have some air in the system or your system is not holding pressure, allowing the coolant to boil. Make sure that you bleed from all three points. If your coolant level is returning to normal and not dropping when cold, you should not be leaking anything.
I have to put a tiny amount of coolant in mine, maybe about an eggcup full every six months, I put it down to the expansion cap venting.
I do have a system pressure testing kit and even this shows a gradual leak over with the pressure dropping from about 1.5 bar to 1 bar in about 15 to 20 mins. No signs of coolant loss anywhere though.
One thing to remember about expansion caps is that they are quite cheap and nasty, and some maybe have been on shelves for years. For what they cost it may be worth having two or three handy just in case your new spare is not up to scratch.
Finally I did convert a spare expansion tank to test expansion tank caps, with a small pressure transducer built in. They pop pressure at between 1.2 and 1.4 bar.

Pressure testing kits are quite reasonable on e-bay.




Testing a cap


Sundance