15 replies to this topic

[JELMorgan]

Hi all,

I've recentaly changed my coolent and since the engine seems to be getting very hot. The temperature gauge is showing normal temp but when you turn the engine off it's bubbling up in the expansion tank. The water must be circling because the rad is getting hot and the fan is coming on when it should be.

I thought there might be air in the system but don't know where to blead it.

If anyone has any ideas I would be very greatfull.

Thanks

[minicooper1.3i]

Hey

Can't offer any explanation I'm afraid, but I too recently changed the water / coolant in my MPi and last weekend after about an hours gentlish driving I pulled up and stopped and had the exact same thing. Took me a while to work out where the strange bubbling noise was coming from. It's only done it a couple of times so far, and like you, the electric fan is working fine and the temp gauge never goes more than half a needles width over norm!

Could it just be another lovable MPi characteristic?

[tony kenobi]

this happened me last summer, ended up my rad was knackered. while i was at it, i replaced the thermostat and water pump. but the main thing seemed to be the radiator. it maybe wont do any harm to take it out and run a hose thru it so you can see how much water is actually getting thru. Winter brings problems of rain=rust and cold starts, summer brings overheating,lol.

[minicooper1.3i]

this happened me last summer, ended up my rad was knackered. while i was at it, i replaced the thermostat and water pump. but the main thing seemed to be the radiator. it maybe wont do any harm to take it out and run a hose thru it so you can see how much water is actually getting thru. Winter brings problems of rain=rust and cold starts, summer brings overheating,lol.

Good point! I must admit I didn't flush the cooling system before refilling it. When I drop the new engine in, I'll make sure I do and pay special attention to the rad and heater matrix.

Cheers!

[redhotmini]

may be worth getting a high capacity rad, hythe performance do them. theyre £235.00 but well worth it - fitted one in my mpi, i can actually do 70mph all day without needing to switch the heater on to cool it down, and its much better in traffic, just the leccy fan needs switching on (i have it on a separate switch) and its fine.

[lil dan]

i had just come on here this evening to post the same concern. lol

i had just put it down to the hot weather, as on sat night/sun morning around 3:30am, when the air was nice and cool i had no problems at all. when i changed my leaky water pump the other week i flushed the system too.

[rossikey]

Strange thing is I had the very same issue at the weekend after changing my cylinder head. After looking into the issue the root cause of the problem I believe was due to trapped air in the coolant system. After it had done it for the second time in two days I let the engine cool and then refiled the system and then disconnected the return pipe from the heater to the bottom hose go someone to start the engine and allowed the engine to run until water was being pumped out of the hose. Once I had refitted the hose and topped up the system the car has run without any issues.

I always find you have to bleed the coolant system like this on the older minis also to achieve good cooling but am also suspect that when they removed the heater outlet from the left had side of the head you could end up with an air lock within the head.

Hope this helps.

[miniboy1971]

Strange thing is I had the very same issue at the weekend after changing my cylinder head. After looking into the issue the root cause of the problem I believe was due to trapped air in the coolant system. After it had done it for the second time in two days I let the engine cool and then refiled the system and then disconnected the return pipe from the heater to the bottom hose go someone to start the engine and allowed the engine to run until water was being pumped out of the hose. Once I had refitted the hose and topped up the system the car has run without any issues.

I always find you have to bleed the coolant system like this on the older minis also to achieve good cooling but am also suspect that when they removed the heater outlet from the left had side of the head you could end up with an air lock within the head.

Hope this helps.

Thanks for posting your advice on this problem. Mine has run like this for years.....I'd like to try your suggestion for bleeding out the air, but not exactly sure what pipework you're refering to w.r.t return pipe and bottom hose (sorry I'm not that bright) any chance of a picce or maybe elaborate a bit more...cheers....

Also, would it be worth running the engine with the cap off the expansion tank to let some of the air bleed out here (being the highest point for air to escape?)......obviously not letting it get too hot/steamy and risk any antifreeze/water bubbling out on to the paintwork....or does it have to stay pressurised.....

Thanks....

Village Idiot for Kent

[JELMorgan]

Thanks for all your help. I'll try bleeding it I think and i'm gonna put a new thermostat in whilst i'm under the bonnet.

Cheers.

[rossikey]

Miniboy,

I don't have a pic to show to hand but if you look at your thermostat housing you will see a 3/4 inch pipe (Approx) leading from the housing towards the bulk head. If you follow this back to the bulk head when you get to the fuel pipes you will see another pipe that looks the same coming from the bulk head leading into the bottom hose as it goes into the water pump inlet.This is the return hose from the heater. At this point there should be a join in the hose with a spring type clip which is where you need to disconnect. I must stress to do this though when the engine is cold to reduce the risk of being burnt by hot water. Also ensure you have the heater control inside the vehicle turned onto hot.

As for the radiator cap it is important to ensure the cap is fitted and working correctly. If you leave it of it wont help with a air lock situation. If however you bleed the system and still have an issue I would also ensure the cap is working correctly.

Good look.

[bigmotherwhale]

i think i know what the problem is, the mpi has a pressurised coolant system and therefore the boiling point of the water is higher than 100 if the system isnt pressurised then it will boil over before the fan even comes on, happned to me took ages to find the problem was the top cap for the expansion tank which has a relif valve thats prone to stiking i got one of an old metro and i never had the problem again, hope this helps, just get a new topcap.

[JELMorgan]

Yea i did think about changing the cap. Sounds a good idear.

Thanks for the help!

[miniboy1971]

i think i know what the problem is, the mpi has a pressurised coolant system and therefore the boiling point of the water is higher than 100 if the system isnt pressurised then it will boil over before the fan even comes on, happned to me took ages to find the problem was the top cap for the expansion tank which has a relif valve thats prone to stiking i got one of an old metro and i never had the problem again, hope this helps, just get a new topcap.

Just thought I'd let people know that I followed your sage advice and replaced the black cap on the expansion tank.

I didn't even realise this cap had a valve inside and when I took the old one off and had a look underneath, the brass diaphragm was really corroded and covered in crud.

I've had the car since new and never replaced this myself and suspect it is the original one. I doubt Rover would have changed it, as I was lucky if they even changed the oil for me when they serviced it....!!!

I took the car on the L2B run last weekend and been out in it today. It's been warm both days and whilst the fan has come on, the coolant has not been boiling as it did before and I think the car was running much nicer as well (although this might be placebo effect !!)

This seems to have solved my problem at least.....and the constant boiling may have even have contributed to me going through two water pumps in quick succession...?????

This may not solve everyones problems, but it's the cheapest and easiest one to try first....

Thanks Bigmotherwhale...!!!!!

[redhotmini]

a lot of problems seem to be caused by the expansion bottle caps, either duff old ones, or ill fitting ones. if you cant get genuine rover ones, minispares sell the only ones that fit properly now

[miniboy1971]

Amazing that a simple cap could cause this problem....I got a genuine Rover one for about £ 6.

I wouldn't have suspected this in a million years.....

A great example of how good these forums really are....!!!