2012 MINI Cooper S Major Over Heating Incident/Engine Rebuild
This "Pepper White" 2012 MINI S arrived after some bad luck. We seem to get a lot of white/cream colored MINIs around here. Must be a popular color.
The owner reported traveling down the interstate when the car suddenly shut down. The owner had it towed to a local Firestone/Meineke type shop for repairs where they noticed that the thermostat housing had failed. So they installed a new one. Once they were done with the installation process, they attempted to crank the car up. The engine tried to spin over, but stopped. At this point, the Firestone/Meineke recommended taking the car to a different shop, and backed away from the project.
While their intentions were good, they didn't follow the basic steps of inspection, diagnosis, and analysis of an engine after a really bad over heating episode like this poor car suffered. When the thermostat housings on these car rupture (they're plastic and can crack) they can vent coolant very quickly. This allows the engine to potentially run very hot before the car can be safely shut off. In this situation, the engine actually stopped running due to the overheating. That's not a good sign.
Usually when a car arrives here after overheating issues we plan to run a compression test on the engine, a pressure test on the cooling system, and to inspect the coolant for any signs of combustion gases in the coolant. Our concern is that the overheating incident had led to a failed head gasket, which will lead to coolant entering into the combustion chambers and coolant getting into the combustion chambers. Hot exhaust gases will overheat and over-pressurize the cooling system, and coolant entering the combustion process can lead to all sorts of rough running/engine damage situations. The head gasket makes sure these two things stay in their respective systems, and a leak in that gasket is not good news.
Knowing the car had badly overheated, and knowing that the previous shop had not bothered to check for engine damage before beginning repairs, we first pulled the spark plugs out. We could immediately see that the chambers were full of oil and coolant, which is absolutely not a good sign. With that amount of liquid in the combustion chambers, it was likely that the vehicle's engine had been "hydrolocked" either during the over-heating process or afterwards when it tried to crank and stopped. This will lead to bent valves and bent rods.
It was also interesting to find so much coolant still in the engine. With reports of a cracked thermostat housing, you would expect most of the coolant to have leaked externally. We would need to look closely at the engine.
The owner reported traveling down the interstate when the car suddenly shut down. The owner had it towed to a local Firestone/Meineke type shop for repairs where they noticed that the thermostat housing had failed. So they installed a new one. Once they were done with the installation process, they attempted to crank the car up. The engine tried to spin over, but stopped. At this point, the Firestone/Meineke recommended taking the car to a different shop, and backed away from the project.
While their intentions were good, they didn't follow the basic steps of inspection, diagnosis, and analysis of an engine after a really bad over heating episode like this poor car suffered. When the thermostat housings on these car rupture (they're plastic and can crack) they can vent coolant very quickly. This allows the engine to potentially run very hot before the car can be safely shut off. In this situation, the engine actually stopped running due to the overheating. That's not a good sign.
Usually when a car arrives here after overheating issues we plan to run a compression test on the engine, a pressure test on the cooling system, and to inspect the coolant for any signs of combustion gases in the coolant. Our concern is that the overheating incident had led to a failed head gasket, which will lead to coolant entering into the combustion chambers and coolant getting into the combustion chambers. Hot exhaust gases will overheat and over-pressurize the cooling system, and coolant entering the combustion process can lead to all sorts of rough running/engine damage situations. The head gasket makes sure these two things stay in their respective systems, and a leak in that gasket is not good news.
Knowing the car had badly overheated, and knowing that the previous shop had not bothered to check for engine damage before beginning repairs, we first pulled the spark plugs out. We could immediately see that the chambers were full of oil and coolant, which is absolutely not a good sign. With that amount of liquid in the combustion chambers, it was likely that the vehicle's engine had been "hydrolocked" either during the over-heating process or afterwards when it tried to crank and stopped. This will lead to bent valves and bent rods.
It was also interesting to find so much coolant still in the engine. With reports of a cracked thermostat housing, you would expect most of the coolant to have leaked externally. We would need to look closely at the engine.
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We suspected from the evidence that this car would need more than just a standard head gasket repair, and planned on an "in-car engine rebuild". It was planned around being a very similar repair to this project. The main difference would be whether or not we would need to replace any valves or connecting rods as well as the other components.
Also, just like the previous rebuild, we will be addressing weak points in the cooling system and turbo/oil filter housing seals while we are going this far into the engine. The car will also receive the equivalent of the walnut-shell treatment to the intake valves, since the complete head will be cleaned, decked, and have any damage valves replaced along with the valve seals. |
It looks like we have a pretty big project in front of us, so as always, it's time to get to work.
Stage 1: Disassembly
The engine head will need to be removed whether or not the whole engine needs repair, so we'll start there. With a leak this egregious, there's a chance that the head is not only warped, but cracked. It will need to be closely inspected. There is also a possibility that the engine block is warped. The block warping is quite rare. Older vehicle's with iron blocks are even safer, but this modern engine with an aluminum block may have some warping since this was a badly over-heated engine. We'll look closely at that too. Follow along in the picture gallery to see the process.
Stage 1: Disassembly
The engine head will need to be removed whether or not the whole engine needs repair, so we'll start there. With a leak this egregious, there's a chance that the head is not only warped, but cracked. It will need to be closely inspected. There is also a possibility that the engine block is warped. The block warping is quite rare. Older vehicle's with iron blocks are even safer, but this modern engine with an aluminum block may have some warping since this was a badly over-heated engine. We'll look closely at that too. Follow along in the picture gallery to see the process.
Stage 2: Inspection and Parts Planning
The head was inspected, and was of course warped. It was re-decked to make it true again, received new valve stem seals and had valve lash set, and was completely cleaned.While it was off, it was noted that an internal freeze plug had come loose due to the severe over heating. This is not an unheard of problem with MINI heads. It also explains why more coolant wound up inside the oil system than vented to the outside when the thermostat housing cracked. It's hard to know which part failed first, but it's even more clear that this was a very bad over-heating cycle. The freeze plug was replaced with a threaded plug that is held in with epoxy. It should never be a problem again.
While the head was off the car, we were able to verify that the block was still true. This was very good, since removing the block completely from the car and having it resurfaced is a much more difficult/expensive process than doing the same basic thing to the head.
It was observed that the connecting rod bearings were not as good as they should be for 63k miles. This was most likely due to the accelerated wear they experienced when all the coolant and oil mixed together ruining the viscosity and lubrication ability of the oil. Turbos MINIs are harder on their internals due to higher than average oil consumption. Due to this, we plan to go ahead and replace the piston rings. Fortunately the cylinder bore does not appear to be damaged by the contaminated oil that the car ran on.
MINIs have weak timing chain chains and other components that are sensitive to heat. Running low on oil, having low oil pressure, or contaminated oil allowing them to get too hot. So will a bad over-heating episode. This MINI experienced contaminated oil and was badly overheated. It will get new timing chain components.
MINIs use plastic components in their cooling system that like to fail as early as 60k miles. These components were stressed by a bad overheating episode. Most of those parts are removed to service engine as well. Since the vehicle had 63k miles on it, it was agreed to go ahead and replace the known weak points in the cooling system.
The turbo oil feed and drain lines, and the oil filter housing, are known oil leak points. The oil leaks can get pretty bad because they are under pressure. While an over-heating episode would probably not cause a leak or make it worse, all the parts have to come off for this repair. It's a great time to go ahead and invest in new/improved seals to prevent leaks in the future.
The head was inspected, and was of course warped. It was re-decked to make it true again, received new valve stem seals and had valve lash set, and was completely cleaned.While it was off, it was noted that an internal freeze plug had come loose due to the severe over heating. This is not an unheard of problem with MINI heads. It also explains why more coolant wound up inside the oil system than vented to the outside when the thermostat housing cracked. It's hard to know which part failed first, but it's even more clear that this was a very bad over-heating cycle. The freeze plug was replaced with a threaded plug that is held in with epoxy. It should never be a problem again.
While the head was off the car, we were able to verify that the block was still true. This was very good, since removing the block completely from the car and having it resurfaced is a much more difficult/expensive process than doing the same basic thing to the head.
It was observed that the connecting rod bearings were not as good as they should be for 63k miles. This was most likely due to the accelerated wear they experienced when all the coolant and oil mixed together ruining the viscosity and lubrication ability of the oil. Turbos MINIs are harder on their internals due to higher than average oil consumption. Due to this, we plan to go ahead and replace the piston rings. Fortunately the cylinder bore does not appear to be damaged by the contaminated oil that the car ran on.
MINIs have weak timing chain chains and other components that are sensitive to heat. Running low on oil, having low oil pressure, or contaminated oil allowing them to get too hot. So will a bad over-heating episode. This MINI experienced contaminated oil and was badly overheated. It will get new timing chain components.
MINIs use plastic components in their cooling system that like to fail as early as 60k miles. These components were stressed by a bad overheating episode. Most of those parts are removed to service engine as well. Since the vehicle had 63k miles on it, it was agreed to go ahead and replace the known weak points in the cooling system.
The turbo oil feed and drain lines, and the oil filter housing, are known oil leak points. The oil leaks can get pretty bad because they are under pressure. While an over-heating episode would probably not cause a leak or make it worse, all the parts have to come off for this repair. It's a great time to go ahead and invest in new/improved seals to prevent leaks in the future.
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The Parts List: Timing Chain Kit: Chain Tensioner Crank Timing Gear 1 Tensioning Rail 2 Guide Rails Crank Bolt 2 Cam Shaft Bolts and 3 Timing Chain Guide Bolts Cooling System: Water Pump Coolant Pipe Water Pump Drive Wheel Coolant Head Parts: Valve Stem Seals Cam Cover Gasket Head Gasket Various Sensor/Component O-rings and Gaskets Head Bolt Set Block Parts: Connecting Rod Bolt Set Connecting Rod Bearing Set Piston Ring Set Oil Pump & Pan: Oil Pump Chain Oil Pan Gasket Miscellaneous: Exhaust Manifold Gasket Downpipe-to-Turbo Gasket Downpipe-to Midpipe Gasket Intake Manifold Gaskets Oil Filter Housing Gasket Set Turbo Oil Lines |
A loose freeze plug in the head, center of picture, was exposed during the cleaning process. This happened when the head was badly over-heated.
The hole was tapped for a new plug.
The new brass fitting installed with some epoxy. Space is tight, so the epoxy may not be pretty, but it is functional.
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Stage 3: Reassembly
So, with the head cleaned and ready, and the block found to still be true, it's time for reassembly. We'll start with honing the block. Then install the piston rings and connecting rod bearings, which are discussed in more detail here, and then the oil pump and oil pan. From there it's the engine head, timing chain components, cooling system parts, turbo, exhaust, oil filter housing, etc. Follow along with the picture for a more step-by-step guide with comments.
So, with the head cleaned and ready, and the block found to still be true, it's time for reassembly. We'll start with honing the block. Then install the piston rings and connecting rod bearings, which are discussed in more detail here, and then the oil pump and oil pan. From there it's the engine head, timing chain components, cooling system parts, turbo, exhaust, oil filter housing, etc. Follow along with the picture for a more step-by-step guide with comments.
So the beast lives! We buttoned up the front end, which meant attaching the bumper skin, windshield washer bottle, and several electrical connectors. Further test driving showed that the car felt nice and peppy. It's hard to know how well it drove before the work since it was dead on arrival, but we know it feels like a MINI S should. Now it's time to go back to the owner.
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