vs
Thermostat OEM Audi or MISHIMOTO
I finally got around to installing a new thermostat/o-ring/housing and coolant reservoir/cap yesterday. When removing the thermostat, I noticed that the bottom bolt was VERY loose... I had done the thermostat without housing about a year ago now, had never leaked coolant before... My best guess is that I just didn't torque it enough and it slowly loosened, but only when cold (just a guess, but would help explain why no drips when car was running on ramps) and in small enough amounts that I did not notice a puddle on the ground.
Pros: issue resolved, no coolant loss
Cons: bottom bolt was loose
Vehicle:
Audi TT
I had a 96 and have done that job twice, make sure replace the thermostat otherwise it's a do-over several months later because you tried to save $20. Been there etc!! Change the belt, tensioner, water pump and thermostat.
Cons: do-over several months later
Vehicle:
Audi A4
My Q5 with 75,000 miles on it developed a leak in the water pump area. Initially Audi denied there was a leak, so I took pictures and showed it to them. Then they diagnosed it with thermostat leak.
Pros: warranty on that part
Cons: leak in water pump
Vehicle:
Audi Q5
Mileage: 75000 km
mishimoto changed the design of the thermostat when I purchased and you will need shorter bolts they are not provided
Cons: design change, bolts not provided
I got a bad mishimoto thermostat with similar results.
Cons: faulty unit
Vehicle:
Subaru
I bought and installed a Mishimoto thermostat that activates at 68°C, while my vehicle OEM (Original factory) thermostat activates at 88°C and fully opens at 100°C. With the Mishimoto thermostat (68°C), the coolant temperature basically stays 71 ~ 74°C when driving, from OBDII reading. Short Term Fuel Trim was OK, between -10% and +10%. I checked the spark plugs after one week, they were fine.
However, after three weeks (last Saturday to be precise), the Check Engine Light was on when I started the vehicle, and OBDII gave Code P0128. I searched the code online and got: coolant temperature fails to reach the proper operating temperature, or Coolant Temperature Below Thermostat Regulating Temperature. My thinking was the engine finally realized that the temperature was below the operating temperature, due to the Mishimoto thermostat.
Cons: caused CEL P0128, engine below operating temp
Vehicle:
Mitsubishi Galant
The current plastic thermostat looks a little more beefy, but is still shatty plastic. They're commonly failing at 30-55k miles in the stuck closed position, instant overheat.
Pros: more beefy look
Cons: shatty plastic, instant overheat
Vehicle:
Audi A6
Mileage: 55000 km
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