Hi again,

I got my car all back together and it seems to be running well, however, after 30 minutes or so I'm often getting overheat warnings and coolant temps up to 119C. The dashboard warning pops at 118C.

History: I recently replaced the AC compressor, then completed the timing chain, valve stem seals, and I did the walnut shell blasting to clean out the gunk and carbon under the valves. Oh, I also replaced the serpentine belt as there was a good amount of cracking on the old one. I then cleared the VANOS adaptations. I don't know why the car is running hot, I didn't mess with any of the radiator or coolant system aside from removing/replacing the existing friction wheel to get to the timing chain guide bolts. I checked and replaced my coolant sensor and there's no issue there, there's no leaks that I can detect and I'm not losing coolant after a few days of test driving. I've tested for exhaust in the coolant with a test kit and there is none detected, and there is no moisture in the PCV cover. I've bled the coolant system via the bleeder screw to check for air bubbles and I'm not seeing any. I could use some advice on next steps. Here's what I'm planning:

Drain coolant, refill, bleed, run the heater with the car off for a few minutes, and refill/bleed again and see if this lowers the coolant temp, coolant is currently blue and pretty clear. (if this doesn't work then)
Replace friction wheel as maybe this was damaged when I removed and replaced it. (if this doesn't work then)
Replace the water pump (if this doesn't work then)
Upgrade the intercooler but there wasn't any significant carbon or oil in the stock intercooler which I thought was a possibility with all of the blue smoke from the failed valve stem seals. (if this doesn't work then)
I don't know what's next, pressure test the system from the expansion tank? Any advice?

 

If you replaced the AC / alternator belt, triple check that the friction wheel is turning the water pump pulley. Maybe it didn’t get reset after that work and the water pump isn’t spinning?

 

Thanks for this advice. I think the friction wheel is probably the issue. I doesn’t seem to be moving like the way it is demonstrated in this video:

 

Update: I replaced the friction wheel and the water pump pulley, didn’t solve it. Still was hot. So I replaced the fan (I noticed that Stage 1 wasn’t kicking on), didn’t solve it either. I have a thermostat and water pump coming today or tomorrow.

BUT… I was chatting with an AI bot I instructed to read up everything it could on Mini Cooper S R56 N18 and through it’s questions back and forth I explained the horrific 30 seconds or so the car was idling without the oil pump turning (I had let the chain slip off by accident during the timing chain replacement) and it (the AI) is telling me that this would have possibly (likely?) damaged the bearings, pistons rings and scored the cylinders, and could be causing add’l friction even though the engine seems to running beautifully. It suggested I go check the oil for different colored bits of metal. When I dropped the oil pan to replace it (the previous owner had cross threaded the drain plug) I noticed some shimmering bits of metal, but it looked to be from the oil pump chain spinning off the sprocket … but now I’m not sure. I’m going to drain and inspect the oil today… god help me.

I am going to finish the water pump and thermostat, and if this doesn’t fix the overheating issue, and/or I find a lot more metal in the oil pan. What all do I need to replace/do to make sure I don’t destroy my engine? I was already looking into the connecting rob bearings, and the piston rings, and a high grit re-honing. Does anyone know if I can get at the crank bearings (are these the “main bearings”)?

 

Yikes, that is not good. Indeed, irreparable damage is possible. Alas, might also get away with it.

If you're going to go for rebuilding it with all new bearings, pistons, hone job, it's probably worth it. Generally at this point boring cylinders over is advisable instead of hand honing.

You could also do a couple of short run oil changes trying to clean it out, and if you still have good compression, maybe just run it until rod knock occurs (if it will).

You mentioned no air bubbles from coolant vent plug. Not sure how you'd see any bubbles, but usually want to fill until coolant is flowing from vent plug then tighten. Air in the system is a real possibility. Note, my experience is specific to the N18 engine which isn't identical.

I'm no expert, just noticed you've been alone for minute.

 

very kind of you to reply. I’ve replaced the pump, the pulley, the friction wheel, the thermostat and I flushed the coolant. The coolant wasn’t nasty just old and the new coolant (been drained and replaced since I went back and did the pump and thermostat after the previous round of fixes didn’t fix the issue. I’m going to park it on an incline (engine up) and try to vacuum and bleed the coolant again so I can rule out air in the system.

I am not confident that this is going to resolve it so I’m back to concerns about excess friction due to my idiocy of starving the engine of oil for a few minutes. It’s a BIG job to rebuild the engine but I think I could pull it off. Obviously if the cylinders are gouged really badly this is pointless and I’ll have to shop for a replacement block. I’m hoping this would just be honing and measuring the cylinders (N/S, E/W and top, middle bottom) vs the spec. Then I’ll have to plastigauge the gap between main bearings and the con rod bearings to see if I need to replace the crankshaft. If the block and crankshaft are serviceable, I drop the oil pan, remove the oil pump,the oil drain plate thingie, remove the con rod caps, and crankshaft, replace the bearings, replace the pistons and piston rings all the damn gaskets (there’s decently priced kits for all of this) and I replace all the TTY bolts put it all back together and HOPE that it runs cooler. God help me, but I think I could pull it off.

are there any other things I have to replace if I’ve got the block apart? And am I insane? I have to admit I love that little car.

 

The vacuum coolant fill seems pretty surefire from what I have read. Certainly not a bad plan.

I personally DON'T think excess friction from the moving components group (via lack of oiling) would cause overheating. Feel pretty solid about that honestly. If that much heat was being generated, it would have to be piston/ring to wall fit, while the outside of those walls are nearly surrounded by flowing coolant. I think the engine would be making some fun noises or nearly be seizing for that level of heat.

To the above point, a borescope camera purchased from amazon down through the spark plug holes to examine cylinder walls would be a SUPER cheap step before assuming the cylinder walls are trash and ripping it apart. Super cheap relative to the work in tearing it apart. It IS a big job to rebuild the engine. I half-assed DIY'ed mine last autumn, where the block stayed in the car, pistons out, crank in and covered, honed, all the rest of the good stuff. It ran great for about 10k and is having other problems seemingly unrelated to my work. So I have some experience with what you're looking at. Mine started with a misfire and one cylinder with slightly low compression, but a bunch of carbon sitting on top of a piston.

I can't help say what you might've missed in your list, sorry. However it does seem like you've done your homework. Mind you, you have a lot of torque spec's to find in that list. I REALLY think, coolant problems are more likely, and a borescope in the cylinders (rotate crank by hand if needed) is cheap insurance against spending on a rebuild.

 

Thank you so much for this response. This could save me days and days of work and ~$500 in tools and parts. I do suppose I withheld one piece of info, though. After the incident and I got into the oil pump and took off the plastic sprocket cover to see the chain dangling, I kept pouring the oil over the engine (a few times to try to fill the galleries) and hand cranked it over and over again. It did feel a little tougher to turn but just a tiny bit. I'll keep working on the coolant/radiator system and see if I have a blockage in the radiator or something. After that, I'm out of things to change. There are still no codes and no leaks.