Heater

Making The Heater Heat

This is really a follow on from the item about fast Idle. The cooling system of the MR2 includes the Throttle Assembly and the in car Heater in the "primary" circuit such that the main radiator is only active after the thermostat has opened, which will only occur when the primary circuit reaches about 95 degs Fahrenheit. This has some strange effects. The fast initial idle is likely to stay fast for longer if the heater is operating efficiently and with the blower on.

Having had the car about a month now, (16/10/00), no really cold weather has been experienced, but trying the the heater out revealed it just wasn't getting as hot as most car heaters do. It seemed appropriate to give the heater the same treatment as the heater in the throttle assembly, that is a good reverse flush.

It should mention that just before the MR2 became mine, the head gasket had been changed and the cooling system refilled. I do not know if the complete system was reverse flushed, but even if it was, the tributaries of the throttle heater and the main car heater would probably be difficult to clear.

The procedure followed was as below:

Remove the spare wheel and pull clear the carpet trim from the wheel well. Remove the two rubber plugs from the bottom of the well.

Take off the trim surrounding the brake cylinder, fuse box etc.

Locate the heater connections; the easiest ones to get undone are the two at the bottom, one going to the heater directly and the other to the heater via the on/off valve.

With the system cold and the radiator cap still in place, slacken the clamp on the right hand hose. Its easiest to undo this enough to drop the clamp down and off the hose rather than pull it back up the hose. The hose will probably appear to be stuck on the pipe, and gently gripping the hose with a mole wrench and twisting will release it.

Once the hose will move, break the connection. Some coolant will come out but not a lot if the radiator cap is still in place. Plug the bottom pipe temporarily using a screwed up piece of polythene or similar. You could make up proper plug stubs as in item 1, but it didn't seem necessary.

Do the same with the left hand connector and plug the pipe in a similar fashion.

If a garden hose is now connected to the left hand heater connection (making sure first that the heater control is turned on), fairly clear water will probably come out of the right hand hose. Reverse the connections though and really brown and generally mucky water will come out of the left hose. For my car this brown flow continued for nearly a minute before clearing. Reverse the hose flow a few times until clear water comes out in each direction.

Re-connect the hoses, and carry out the cooling system fill procedure as described in the vehicle hand book or in many places on the web. This involves using the lengths of polythene hose and making sure all air is removed from the heater and radiator cooling loops.

Start the engine and see how well the newly cleaned heater performs. The heater on my MR2 is now so efficient that if the blower is left on full, the engine temperature is kept below that at which the thermostat opens, even after 15 minutes of running. I thought I had an airlock in the radiator as it remained completely cold during this test and only when the heater was turned off did the thermostat open and the radiator start to warm up.

A good procedure to carry out before the winter sets in.

(16/10/00)