A couple days ago I got a coolant flush. Since then, theres been a few times where the yellow high temp light comes on for a few seconds, then goes off, and the temp runs in the norm for the rest of the drive.

This only happens after the car is first started and the engine has warmed up. Once the temp hits about 185F it quickly spikes to about 240F, then drops just as quick as it comes up, assuming the fan kicks on and/or thermostat opens.

The thermostat is working properly as the water temp plummets when I hit the max A/C button, forcing the thermostat open. The fan works as well, both low and high speeds.

Could these temp spikes be due to air in the coolant system? I'm not leaking any coolant as far as I know, and everything else seems to be working properly, so I'm at a loss. I thought I bled the system well enough, a couple times now, but apparently, I havent. Any tips on bleeding properly? I run the heat on high at first to get coolant into the heater core, then hit the max A/C button to open the thermostat to get coolant running through the block, all with the bleeder valve open on the thermostat housing. The bleeder valve bubbles and sputters coolant, then stops.

Am I missing something else?

Thanks,
Nick

 

The thermostat cannot be forced open except when it reaches its predetermined temperature. But for the sake of your issue, let's assume it is good and installed correctly considering you didn't touch it and you did have a flush.

Absolutely. Who did the flush and how? If it was someone unfamiliar with Mini's, my guess is that your problem is air in the system.

Rich

 

Hi Rich, thanks for the reply.

I've read a number of posts on this forum about the thermostat being electronically controlled, and hitting the max A/C button forces the thermostat open (not sure if its actually electronic or not, but turning on max A/C does drop the temp by nearly 20 degrees...maybe just due to the fan kicking on). I havent done anything to the thermostat, and it appears to be working, though maybe just sticking.

The shop that did the coolant flush is a place that claimed to specialize in European cars like BMWs and MINIs, but I dont think the guy that worked on my car had any experience with MINIs. He told me the coolant kept over flowing and that I had a blown head gasket because he was seeing air bubbles pushing into the coolant expansion chamber.

The car runs too well and theres no signs of a blown head gasket, so my guess is he got the car up to temp without the expansion tank cap on, and was basically boiling the coolant, hence the bubbles.

I bled the car when I got home and the temps stayed where they should for a couple days. But on the 3rd day I used the A/C, temp stayed at normal till the next time I ran the car, then it spiked again once it got up to temp. How much air could possibly be in the system? I've since bled it again, but the temp spiked again during the next drive.

I'm bringing the car to a Mini dealer to get a recall fixed (auxiliary water pump), so I'll ask them to do a compression test to verify there is no blown gasket, and to bleed the system properly...I must be missing something.

 

this statement is incorrect. Old fashioned "theromstats" do not have a way to be forced open. But on this car it is a very complicated and computer controled heart like device that directs water in a number of different directions depending on the status of things like the A/C being on. So yes it can be forced open.

 

I stand corrected. Sorry.

Perhaps the moderators can take down my post.

///Rich

 

To the OP. The collant should run at about 220 most of the time unless the A/C is on then it may run cooler.

As for the techs comment about the head gasket and bubbles. Well if not bleed properly then bubbles will come up in the expansion tank from time to time.

MINI recomends a vacum bleed on the cooling system. But as i dont have one i kept squeezing the radiator tubes until the car stopped taking in anti freeze from the overflow tank. Have never had a temp problem doing it that way.

 

What has failed to be mentioned here is that the bleeder screw must be opened on the thermostat housing while the coolant is SLOWLY poured into the coolant expansion tank. This is the best way to purge air from the system. When I flushed mine last winter, I lifted the expansion tank about 6" higher than where it normally sits to aid in filling the system. You need a flashlight to see the small bleeder screw but you can tell when there are no more bubbles coming out just by judging from the flow coming out of it. There are a lot of harnesses in the way from seeing it clearly so a flashlight helps a lot.

It sounds like you have an air problem. The best way to be absolutely sure there are no bubbles is to crack the bleeder screw and start pouring more coolant into the expansion tank and observe the flow.

I love how the tech said you had a blown head gasket and that's why there are bubbles in the expansion tank. It's called AIR buddy and you didn't purge it :-(

 

I agree it sounds like air in the system.

 

Read the first post, third paragraph, last line. It states "all with the bleeder valve open on the thermostat housing"

 

I'm having the exact same issues, and was about to make a post - the temperature blips high (I actually get the red alarm light) and then within a few second drops back to 185. Here's what I've noticed:

• It happens at complete random, usually after the engine has heated up. It can happen after a short drive or a long one; in stop and go traffic or at highway speeds. It happens a little more often when the weather is warm.
• Once it happens once, it'll happen a lot during that trip. It'll sometimes go away again for a few days - I actually had a three week gap where it didn't do it once and I thought I'd fixed it.
• I've also noticed that when it does happen the AC gets warmer - almost as though the radiator is so hot it's heating up the AC core. The heater is still completely fine.
• Oil temperature never seems to spike during this, but I'm pulling it from the AccessPort and have no idea how it's derived given the lack of sensor.
• It's much rougher driving after a cold start lately, lots of grumbling after the 2k rpm mark - almost as though the system isn't going closed-loop properly. Once the engine warms up it's just fine.
• The fan that runs after shutdown is running on full speed for the full five minutes.
• I have a CEL for Temperature Sensor MAX or something similar.
• No coolant leaks - coolant level is steady. Hasn't suddenly dropped implying a big air bubble got out either.

I've replaced the temperature sensor, figuring that kind of wild spike might point to misreading - no go.

I've bled it repeatedly, and left it running for some time with the cap off... not even getting any bubbles.

This all started shortly after MINI had my engine apart for my timing chain replacement. They never replaced my coolant, and it was slightly black after. They said this was "normal" given the work they'd done (the chain guide shattered, and spread itself throught the engine) and then offered to change it for an exhorbitant fee. I declined.

After the alerts started, I got a coolant flush - but it made no difference. Plus my rad fluid is still slightly dark - my first worry was head gasket, but there's no oil contamination; or coolant in my oil.

I'm wondering if there's something in there gumming up the works - sticking the thermostat open or closed; or possibly having damaged the pump. Is there any easy way to tell if the pump is running?

I'm probably going to pop off the artificial heart next week; but if I don't spot anything obvious take it up to BMW for a poke.

 

Those symptoms (yours and the OP's) sound an awful lot like an air pocket in the cooling system. It makes me wonder if these engines are simply really hard to bleed?

There is a possibility that a leaking head gasket could allow combustion gases to enter the cooling system; this will give the same sort of symptoms as an air pocket. I believe there are ways to test for this happening, like some sort of additive that changes color? Might be worth thinking about or talking to your local techs about.

 

Air bubble seems the most likely... a bit more reading has show that the engines are famously hard to flush and bleed - why Bentley recommend a vacuum bleeder. And I know for a fact the place that did it the second time didn't use a vaccuum.

I'm torn between the techy need to do it myself, or just forking money over to BMW to do it for me. I'll probably do the latter at this point, and pick up a vacuum bleeder later.

I'm tentatively ruling out head gasket leak at this point, there's none of the other symptoms - white smoke, oil in water / water in oil, etc; and as noted there doesn't seem to be any other symptoms of real overheating.

 

You can buy a tester kit to rule out a blown head gasket, but with you'd be one of the first people to report blowing one at such an early time. I hate to be a speculator, but based on the symptoms it sounds like an air bubble is in there and good ole Rickey didn't bleed the system correctly.

 

Took a few hours today and had a closer look at things.

I dismounted and raised the expansion tank and almost immediately got a big bubble. The problem seems to be the design of the connection to the tank - the hose comes in level to the MAX line, then down the side of the tank and into the bottom. No bubble is going to travel down that, and will just get pulled back through the system instead of burping out: it's like the U bend under the sink.

A bit of hose squeezing, a lot of bleeding and filling (with the engine running and not) and I seem to be running a little better now. I'll keep an eye on it over the next few days.

Dismounting and raising the expansion tank during filling looks to be vital. That or a vacuum filler.

 

Update: it came right back a few hours later, so I took it in to MINI today.

The drain screw on the thermostat housing was stripped, letting air back into the system.

Apparently this entails a full thermostat housing replacement (the screw isn't stripped, the housing is). I was quoted at $600... to which I laughed. There are several guides on here on how to do it yourself, and the parts are in the $120 region.

Still a bit of a ****-off though.

 

Thanks for the info, guys.

It was kinda chilly outside this morning so I had the heat cranked up to max, and the water temp didnt spike - simply came up to temp like a car should and stayed there at 220. Tried it again on the way home from work this afternoon and again the temp did not spike. Weird. I'll try lifting the expansion tank.

Anyone have a diagram for the coolant system? I'd like to see how/where the coolant runs through the whole thing.

Thanks for your input on your temp spiking problem, an2, at least I know I'm not the only one. Thats a bummer about the bleeder screw threads being stripped on the thermostat though. Cant believe what some places charge for doing a thermostat change.

 

Welp, I replaced it easily enough (the threads were badly stripped, never going back to that MIDAS again... almost makes me wonder if they took the air wrench to it )

Advice for people refilling - the bleed screw is a bit of a misnomer, and a few of the guides people have reposted (including the one in the Bentley manual) leave out an important step. The official MINI method goes something like this:

• Ignition on but engine off; heaters on hot but slow. (This opens up the heater core loop, so you're able to fill the entire system)
• Remove the bleed screw entirely (This lets air out of the back half of the system while you're filling. I suggest completely removal so you can see what's going on in the next step more clearly.)
• Fill through the expansion tank -slowly- until bubble free coolant comes out the bleed screw hole. (With a light pointing at it, you can see it coming. I also overfilled for a few seconds, just to be sure)
• Put the bleed screw back in, and basically never touch it again. (the system is designed to be self bleeding through the expansion tank hoses - because of how the system is levelled, opening the bleed screw is only effective at releasing very large bubbles - most of the time it actually just lets more air in, and runs the risk of stripping threads. If you're going to do it anyway, squeeze one of the rad hoses to force the water level in the thermostat housing up to the top of the bleed hole while replacing the screw, minimising air trappage)
• Continue to slowly fill the expansion tank to the Max level - raising it and straightening the hose air-lock beneath it can pull out a few extra air bubbles too.
• Start the engine, and after about a minute replace the filler cap. (this lets the pump push through the first few bubbles, and then you can start pressurising the system again)
• Let the engine come up to temperaturethen shut if off. (I actually went for a gentle drive around the block to shake the bubbles loose - I live somewhere borderline mountainous.)
• When the engine has cooled, top up again to full. (I'd dropped to minimum after my first drive - so keep an eye on it. The top of the thermostat housing is actually system level with the min line on the tank; so if it dips below bubbles tend to stay stuck.)
• Keep an eye on it over the next few days, topping up as necessary. (I had a couple of temperature alarms on and off, but they got fewer and far between. Equally I had a couple of small drops on the coolant level, but nothing crazy suggesting a leak.)

After about three days I stopped getting alarms, and I've been almost a week trouble free.

 

That is excellent info, thank you! I'll be giving that a try.