13 replies to this topic

[LukeH]

Hi,

I have a 1997 Mini Cooper MPI that has developed a fault with the cooling system, which resulted in my girlfriend braking down on the way home from a night shift this morning. She called the RAC who was extremely helpful but could not diagnose the problem.

Problem;

The engine keeps boiling over to the point where the water comes out of the cap on the expansion tank however the temp gauge reads quite normal (middle of gauge black line). The strange thing is that even with the engine turned off the water continues to randomly boil up as if there is an airlock or something that keeps forcing pockets of boiling water through.

The RAC guy used a gas analyser to check if the head gasket had gone but that was reading normal. The hose to the side of the thermostat housing (the large black hose) was warm suggesting the the thermostat was opening correctly.

I changed the thermostat last week to an 88 degree rover part due to the thermostat gaskets leaking so I thought I'd renew everything whilst I was there. I also changed the water pump and water pump gaskets plus I flushed the radiator through before refilling with clean coolant.

I'm going to head outside in a moment and remove the thermostat to check for faults but other than that I can't really think of what might be causing the problem. I will perhaps replace the expansion tank cap as I fitted a brand new tank last week but retained the old cap. I'm also thinking of drilling a few holes around the thermostat to allow water to bypass it.

Can anyone suggest what might be wrong or what I could try?

Thanks, Luke.

Edited by LukeH, 27 July 2010 - 10:24 AM.

[WiredbyWilson]

Did you let the car idle after changing all those parts and correctly bleed itself out? As it sounds like everythign else is working as it should.

I would also be suspect of the temp sender if it's boiling up but reading normal.

My appraoch would be to try and re-bleed the system.

[LukeH]

Did you let the car idle after changing all those parts and correctly bleed itself out? As it sounds like everythign else is working as it should.

I would also be suspect of the temp sender if it's boiling up but reading normal.

My appraoch would be to try and re-bleed the system.

Thanks for replying. I have just re-read the official rover workshop guide to re-filling the coolant and I suspect that I didn't fully open the heater control valve which would have casued a huge airlock, so I think you're right and I should re-bleed to see if that fixes the problem.

It's worth mentioning that I have just removed the thermostat and submerged it in hot water but appears to do nothing. I would expect it to open? It's brand new and was purchased from MiniSpares.

Also, it is worth drilling holes around the edge of the thermostat to allow some water to bypass? I've seen this suggested a few times.

Luke.

[AndrewJ530]

Was it hot water from the tap or from a kettle? As 88 degrees is quite hot.

[LukeH]

Was it hot water from the tap or from a kettle? As 88 degrees is quite hot.

Straight from a boiling kettle. I poured it into a container and then fully submerged the thermostat into it.

[WiredbyWilson]

If the top hose was warm per RAC then the stat is working as it should.

Not opening the heater would have caused all manner of air locks - i tend to run with the fan blowing until it is blowing hot air - that way you know water is circulating through it properly.

and once all pipes feel warm i top up the rad to just above the fins and put the cap back on.

[LukeH]

If the top hose was warm per RAC then the stat is working as it should.

Not opening the heater would have caused all manner of air locks - i tend to run with the fan blowing until it is blowing hot air - that way you know water is circulating through it properly.

and once all pipes feel warm i top up the rad to just above the fins and put the cap back on.

Thanks for the tips. I'll be giving it a go shortly.

It's slightly different on the MPI because it has the front mounted rad with expansion tank so I can't fill to just above the fins but there is a 'Max' level mark on the expansion tank.

[WiredbyWilson]

apologies, but don't go above the max mark

[LukeH]

Right I can now confirm that the brand new thermostat that I purchased from MiniSpares is faulty! I have just spent the last couple of hours driving around sourcing parts locally to fit on the Cooper including a new thermostat.

I tested the new thermostat by submerging it in a pan of water that was coming to the boil. After approx 20-30 seconds the thermostat opened. I then tried the thermostat that I removed from the mini and nothing at all, even if I left it in the pan of boiling water for a couple of minutes, so I would say its knackered.

I've bought a new temp sensor plus expansion tank cap and thermostat, so when it stops raining I will go out there and fit it all and I'll report back with how I get on.

Luke.

[stormintrooper]

forgive the ignorance but whats the max for filling a radiator? i always fill it up the the point it "bottle necks" where the cap goes on, is that too much?

[Twincam]

I've always believed its just above the fins...

[LukeH]

forgive the ignorance but whats the max for filling a radiator? i always fill it up the the point it "bottle necks" where the cap goes on, is that too much?

I've always believed its just above the fins...

Your confusing the normal mini radiator setup with the twin point injection setup (MPI) that my Cooper has. The later minis from 97 onwards have a front mounted radiator behind the grill and an expansion tank at the top of the engine bay, much like a modern car.

The 'max' line is the water level for the coolant system. You don't actually pour water direct into the radiator like you would on a older style mini.

Regarding the old style, i always filled to just above the fins on my other mini.

Hope this clears things up a little.

[stormintrooper]

RE the side mounted rad's would over filling cause over heating?

[1984mini25]

RE the side mounted rad's would over filling cause over heating?

On the older side rad ones, you only need to fill to just above the fins.

As when water is heated/under pressure it expands. So if you fill the radiator to the brim, the coolant warms up it has no were to go except out the overflow (if the cap works) or continues to pressurise the system till the next weakest link blows, like the head gasket, coolant hose etc.