Coolant change on an mr2 roadster?

Answer 1

Parked the car so that the radiator drain plug could drain most of the system. I also managed to find the rear engine drain plug (right above the braided part of the lower exhaust pipe) and open it too, though I actually don't recommend doing so, since it's painful to close with a hot exhaust. If you could find a steeper slope, the results should be better, since the biggest problem is that the coolant pipes go over, rather than under, the fuel tank, isolating the low points in the engine and radiator from each other.

Tools required are a 12mm box wrench for the bleeders, pliers for the bleeder cap, and a funnel. On my car, the thermostat bleeder required a socket with u-joint and extension and almost 50 foot-pounds of torque to loosen. The others were no problem.

I set the heater to 90 degrees (as specified in the manual), drained the system, filled with water, ran the engine, and drained again. Then I loosened/removed the 4 bleeders and filled with 1/2 gallon of antifreeze plus one bottle of Redline Water Wetter (which does everything EXCEPT lower the freezing point). Another 2 or 3 gallons of water (from my home reverse osmosis unit) filled it up.

As described in the manual, you need to close each bleeder (10 foot-pounds only!) as soon as the fluid is coming out without air. The order in which this happened on my car was: heater cap, radiator, firewall bleeder, and thermostat bleeder. Next time, I'll wait a half minute or so after the air bubbles stop, because I left lots of air in the system this time. I know this because I needed to add another gallon of water over the next two days to top off the system as the air worked its way out. So don't drive too enthusiastically right after you change the coolant! (On the third day, the fluid level stayed at the Max line.)

I really disliked having coolant spill in the front compartment; on the MR2 they give you clear hoses on each bleeder to avoid this. You just hang the hoses from the hood with masking tape, and the coolant travels up each hose seeking its level. Then you close the valve and you have only a tube full of coolant to get rid of. Much neater, but then the MR2's front compartment is not open at the bottom.

Anyway, the whole job can be done as described in well under an hour, and the results seem to be fine. You WILL spill some coolant on the engine, and so you get a noticeable coolant smell for the first drive. Just be sure to check the fluid for a few days until the level maintains itself, and expect to add some water to top it off for a day or two.