2005 Convertible, 72k. In July, I had the standard bad thermo symptoms -- temp gauge swings up when stopped or idle, drops as soon as I start moving. Thermostat was replaced, everything worked fine for a couple weeks -- then the problem returned. Rad fan works, no coolant leaking as far as I can tell. Since it had worked for a while, mechanic suspected maybe a faulty part, and replaced the thermo again. Worked for a couple days, then problem came back. Suspecting an air pocket, re-bled/filled the system to ensure no air pockets, & confirmed temp gauge was working properly -- and it's worked great for about a week and a half. Today, it started overheating again.

Mechanic wondered if possibly the water pump is creating a venturi effect somehow and sucking in air (since he couldn't imagine air getting in any other way, since it's pressurized -- coolant would be coming out.) Any ideas? Obviously, I'd rather not have to replace the pump.

Other fun, presumably unrelated history: CVT transmission replaced at 57k (MINIUSA did cover that after I "informed" them of the results of my Google searches), 2nd front bumper (courtesy of a crazed raccoon), 3rd windshield, 2nd PS fan ("coincidentally" broke when the dealer replaced the tranny), right cable for soft top has broken once so far, currently on third or fourth oxygen sensor -- yes, I saved the SB I just got in the mail. Needless to say, my spouse is not overjoyed with the car's reliability -- and I'm getting nervous as the new transmission gains mileage, wondering how long it'll last...

 

I'd check the radiator lower brace, if it's broke the weight of the radiator could pull it down and reduce flow in system.

 

No S/C tis a MCc, note CVT replacement.

Might want to have Water Pump checked to be sure is functioning properly. Also check hoses to be sure there is no kink or bind that may reduce flow.

 

Checking the water pump does sound like the best thing to do. The thermostats came out whole, right? There shouldn't be anything in the system that would cause a blockage.

 

Yes, the thermostats came out fine, and everything seemed to flush OK. I'm leaning towards replacing the pump too [edit: assuming the brace is OK/hoses aren't kinked/pinched], but hate repairs done as a guess(especially when they're expensive...)

Also: gnatster, yes, it's a MCc. Meant to clarify that in the initial posting...

 

The mechanic is incompetent if he keeps on replacing thermostats.

I've recently replaced one on my VW New Beetle... it was stuck closed and hot coolant was not circulating to the radiator. Testing a thermostat takes 5 minutes. Remove the suspected T-stat, put in a pot of water and bring it to a boil. If it doesn't start to open, it's faulty. One should also test the new one before installing it.

I think your water pump might be on its way out... the impeller is loose on the bearing. So at lower RPM, it's spinning in fewer revolutions than it should.

 

seemed to be a bit better after the rebleed . are there 2 points to bleed the cooper as there are on the s? one bleeder at front and one up near t-stat.

 

I'd be suspect of the water pump. I've replaced a couple on Cooper non S's

 

Yeah, I think the mechanic who put the third one in didn't bleed it properly, which is why things only improved for a day. Last trip in, the guy with more MINI experience re-bled. Until yesterday, I thought he'd fixed it...

Everything was fine today, though i didn't drive as far (only about 20 miles, vs. yesterday's 100.)

 

you may wanna pressure test for a head gasket .

 

Did I miss it, or has anyone asked about whether or not the auxiliary engine cooling fan is working? There is a high and low speed stage...

 

How do I check that?

 

Water pump is bad.

 

Update, mostly to document in case someone else searches for similar symptoms (I'm guessing it's the pump): I've definitely heard the fan working at two different speeds.

It's interesting (to me, anyway) that it's been working fine most of the time -- like my 20 mi. drive home this afternoon -- but not at others. e.g. 1/2 hour later, a 4-block trip had the gauge creeping up & the fan going full-blast after I stopped the car. A quick check under the hood reveals a reservoir tank close to overflowing, and a radiator that's cool to the touch. You'd think the wp would either work, or it wouldn't.

My wife's car is in the shop, or I'd be taking this one in today. Hard to function without ANY car, though...

 

Today's update: even cold, first thing this morning, the reservoir was full -- which I interpret as meaning there's either something blocking the hose, or an air lock. Since previous flushes/refills have worked for a while, I'm inclined to think air's getting into the system somehow. Since the system is pressurized, though, the only thing I can imagine is the wp's weep hole is working in reverse, acting as a venturi. Can anyone think of another way for an air lock to build up over the course of a couple weeks?

 

Hi!

I think I am having exactly the same problem:

https://www.northamericanmotoring.co...ml#post2873675

 

I'd say keep bleeding it. The up and down temp is from an air bubble passing through the system, make sure the tech turns on the heat while bleeding the two bleeders. Sometimes it takes quite a while to get it all. Or you have a bum head gasket, is yor oil milky?

 

man i can tell you i did a full flush on mine and even after bleeding had air .coincidentally months later i was checking resevoir;pulled the cap and woosh!! air came out . not in , that's a different sound . so do a search on bleeding ; there was something on it a loooong time ago. it explains different ways to get the air out .

 

It's currently getting bled again. Just looking at the hoses, though, really makes me wonder; the upper bleed valve, by the radiator, is a full inch below where the hose enters the rad. What they were thinking? Nobody thought, "Hey, air is lighter than the fluid, maybe we should put the bleed valve at the high point..." Has anyone designed a vacuum system of some sort for doing this?

 

is up bye the thermostat. (other bleeder).

 

Just another quick update. Picked up the car Thursday after getting the coolant bled again. Everything's been fine thus far -- naturally, I'll post if it changes again...

 

Yes http://buy1.snapon.com/catalog/item....re&dir=catalog

I've used one of these multiple times at DIY days at our local MINI dealer. Sure does make the process easy and no bleeding is required.

 

Im not sure if I just missed it... but there are 3 bleeding points on a cooper and 2 on a cooper S... Make sure you get all 3.

 

I thought there were only two -- top left (passenger side) elbow where the hose enters the radiator, and between the engine & battery, behind the fill spout (or whatever it's called.) Where's the third?

 

Bled & refilled again this afternoon, using a vacuum system. The good news: the vacuum held, which leads me to believe the "maybe the WP's weep hole turned into a venturi" theory is unlikely. Worked fine on the way home, so we'll see...