Late Model Radiator

[Fernflex]

Do you guy now any 70, 72 or 75c fan switch that fit the m20 late model radiator?

[jlevie]

The lowest temperature thermo switch I have run across is an 81C type. Normal operating temperature for an M20 engine would be 80C, so I don't understand why you'd be looking for a thermo switch rated that low.

If you are having engine temperature problems, going to a lower temperature thermostat won't solve that problem. All a lower temperature thermostat does is to let the engine start out at a lower temperature. It is the total heat into the the cooling system and it's output capacity that will determine how hot the engine runs under load. Either there is a fault in the cooling system or the radiator is undersized if the engine runs hot under load.

In this case I think you have increased the heat input to the cooling system, but not resized the radiator to match the load.

[E30Gus]

I have the 81C switch and a pusher fan that seems to come on hotter than I would like (between half and 3/4 mark) A lower temp switch would be ideal for me so that the cooling system isn't playing "catch up" while sitting still. I don't know if the switch location isn't ideal and not getting hot enough or what but a lower switch would be a good fix for this.

[jlevie]

Hmm, 80C has the needle of the gauge about half way between the quarter and mid mark. The needle going that high before the fan switches on could mean that the gauge is lying (check thermostat housing and head temperature with an IR or contact thermometer), it could be a bad thermo switch (test in a pot of water while heating and monitoring temperature), or it could be an air bubble in the radiator that results in the switch not being covered with coolant.

[E30Gus]

I'm leaning towards the gauge because I've tried two switches and purged the air out near the switch by loosening it while under pressure. I've been wanting an excuse to buy an IR thermo!