05 R53 can sit and idle and doesn't seem to want to overheat, but after driving for a bit it heats up. Turning on the defrost on hot helps to cool it a bit for a short time...... Thought it was the reservoir and the cap so I replaced both. Still the same.

The car needed a few other things so I tore it down and did / replaced:
Water pump and oring
water pump flange and oring
replaced thermostat and oring
serviced supercharger
changed leaking oil pan gasket
replaced reservoir tank and cap

After replacing all those, still it overheats the same way as i mentioned earlier. Thoughts?

 

Air in system maybe. How did u bleed it? Also did you refresh all other components recently?

 

Radiator? Did you flush it? Did you also doublecheck the coolant temp using a fault reader or something like the Piston/Torque app?

 

So I just took the thermostat out and put it in water and heated it up, it did open after 195 degrees......when I took it out I noticed I left one of the damn bolts out (only put 2 instead of 3 in)

Replaced and put ALL hardware back...filled the system, from teh tank and the front bleeder....capped it and started the car let it run and idle with the heater on..bled it from the bottom bleeder and the top (although no water ever "pissed" out, it would just kinda flow out a little)

Car heated to looks to be about 220....kept trying to bleed front bleeder, again, no real pressure.....was gonna take it for a drive, then noticed the water was starting to push out of the resivoir cap....

this thing is killing me...plugged radiator?

 

Yes sir....while servicing the supercharger, I replaced the thermostat and oring, water pump flange and oring, water pump and oring, reservoir tank and cap as well....

 

Did you use the bleeder valve with the cap on? Mine only really pushed air out when it was up to temp and the cap was on the tank.

My mini did something similar today. 45 minutes from home, temp started to rise and had coolant spewing out of the expansion tank. However, the radiator hose near the front was very cool to the touch. I figured it had to be the t-stat. Pulled it and did the water test, but mine did not open when the water got up to 195+. I had some weird gray crap floating in my coolant earlier. I'm guessing that was the wax that is inside that makes the t-stat work. Anyway, guess it could be the radiator but I would try one more new t-stat before I spent cash on a new radiator. It could be sticking.

Anwyay, I'd drive, get up to 50ish, turn off and coast as far as i could, start, drive, coast, until the temp would start to rise. Then I would pull over to refill. Amazing how much water you lose in minutes of rising temps. I went through 1.5L plus a half case of water in 15 miles. Also took me 3 hours to get home. But, I didn't want to push the temp up too high and warp the head.

Brand new Gates thermostat. toast.


New Gates Thermostat not opening at 205 degrees

Holding closed. Pretty sure it gave up its guts earlier.

 

I mean, I just removed the thermostat yesterday and boiled it, and it did open.....so def isn't the thermostat (I was really hoping it was gonna be the thermostat again)

 

How can you check the radiator?

 

Another note: I drove it a bit at slower speed (50 or less) with the heater on....ran a little hot, not overheating, until the heater air went cold and then it started to overheat....then the air went warm / hot again and the temp dropped (but never back to normal)

 

Well, if the heater core isn't getting hot fluid and the water pump is working (you said its new and there is no way in hell a brand new impeller can rot in a few weeks) and the t-stat tested good, pointing towards a bad radiator. Or a collapsing hose somewhere...good luck with that, only 20 of them on this car. Really only 1 under suction though (that I can think of), thats the lower hose. This car has so many coolant hoses I can't even picture in my head where they all run.

Radiator fan won't affect your heater core, so that eliminates that as the source.

 

Is there a way to test the radiator? Blow water through it somewhere?

 

With this car, I'd say remove that lower plastic shield, disconnect the lower hose. The lower hose is pretty easy to get to without the shield. Then undo the clamp on the left side of the upper hose by the bleeder. Detach the upper hose from the bleeder coupling. Stick a garden hose in the upper hose end, watch the lower opening and see if water is flowing freely out the bottom of the radiator. I mean, it should come out as fast you put it in. If not, I'd hit it with some flush and try again. If you can't get to the hose clamp on the upper you may have to take the bumper off.

 

This guy shows about how much flow to use with the hose. The arc of the water out of the end of the hose should be about 4". In fact, his clog was rejecting inlet flow and had decreased outlet flow as well. Not the greatest video, but you get the idea.

 

Would a head gasket cause it to overheat like this?

 

Filled system angain and just let it idle, no heat.....heated up to "normal" then I noticed water pumping out of the resivoir tank again.....

 

I drove it...noticed the heater would start to get cool, then hot, then cool.....then cool as it overheated

 

Pulled all the plugs and put a camera down each cylinder....after driving (and starting to get hot (i shut it down before it "overheats")...noticed cylinder 1 and 2 are wet inside....3 and 4 look good.....could a head gasket cause the type of overheating I am experiencing?

 

You'd think you'd have a misfire if the head gasket was blown and/or some cross contamination of oil/water. But, it just depends on where the gasket is blown. It is possible that you are pumping air into the coolant and causing overheating. Any white smoke out of the exhaust?

See if your local auto-parts store has a tester for combustion gasses in the cooling system. This test kit has a fluid that will change colors if the combustion gases are present. The old mechanic’s trick is to take off the radiator cap, start the car, and look for bubbles in the coolant. But....we don't have that option.

edit: Apparently you can get it as a free rental tool at Autozone

 

Ya, just not convinced a head gasket is what it is, it doesn't seem to overheat due to loss of water, more so it seems due to flow and then backing up out of the res tank.

 

Checked compression in all 4 cylinders, all about 120…..
So I found the low speed fan relay was bad, and whomever had this car before and spliced in this relay. When the car was running this guy was scalding hot to touch. Would the low speed fan cause a overheat? I am getting a new fan and relay (package)….the high speed fan works fine (verified by putting 12v to it.

 

Yes it would. There was another thread in here just recently on the fan relay. I think you found your problem.

Temp fan switch/relay on MCS

 

so I replaced the entire fan assembly, filled it and it still ran hot. I definitely heard the low and high speed fans....it never fully overheated, but there was a point where water was backing out of the res tank.........also, when I got it back I opened the bleeder and left it open and nothing but air until I had to shut it off

 

Minis normally run right at 212F or slightly higher when idling for any length of time. The factory manual warns against extended idling for this very reason. At highway speed, my '04 S runs a fairly constant 164 degrees but can easily heat to near boiling if the fast-food drive-thru is busy.

 

What do you mean water was 'backing out of the res tank'?

Was it coming out of the overflow? You are bleeding your cooling system with the pressure cap on the coolant reservoir, correct?

 

Blown head gasket or plugged radiator would cause the water to blowback or boil in the reservoir tank.