Radiator Cap

[Strat42586]

What kind of changes should I expect from a TRD radiator cap? I'm seeing minor fluctuations slightly below the middle point of the stock temp gauge, and under full throttle the gauge drops nearly to the 'C'. So is that normal?

[CompanyFlow]

All of that fluctuation from a radiator cap?

[Strat42586]

Yeah. Originally, it would warm up to somewhere between the one-third mark and the halfway point and stay there, although the position between the one-third mark and the halfway point would differ on each car trip. But after the cap, it started acting like described above.

[CompanyFlow]

I think the dimension of the cap allows more/less pressure and could probably dissipate heat better as well.

[yellow86MR2]

your guage is doing that because you got air in the system and or the thermostat is bad.

I'd say air in the system is the first thing to point out.


After a good 15 minute drive, feel the lower front rad hose, if cold, you got air.


Martin

[CompanyFlow]

I was gonna say thermostat, but he said that it happened once he changed the cap. I have heard of people overheating because of a bad cap, perhaps you are "overcooling" so to say.

[JekylandHyde]

If there was air in the system, he would be overheating.

I suspect your thermostat is bad.

[yellow86MR2]

with air in the system temp guage will jump around. If driven for a longer period of time at high rpms, it will start to overheat. Otherwise temp guage will fluctuate. I have seen that on my first mr2. Air pockets passing by the temp guage sender unit cause that.


Martin

[Strat42586]

The gauge has never crossed the halfway mark, even when i boosted around town for 15 minutes.

[JekylandHyde]

Running your engine too cool is NOT good for it.

Your coolant system, when properly bled, does not have air in it and the liquid is under pressure. This increases the boiling point of your coolant/water. If there is air in your system, it will not be properly pressurized; therefore, your boiling point will be lower and your car will over heat.

http://auto.howstuffworks.com/cooling-system.htm
Page 7 explains how air is normally kept out of the system via the radiator cap
Page 8 explains the thermostat

Strat42586, your thermostat is either stick open, is leaking or is opening prematurely.
Either way your system is seeing all of your coolant most of t he time and it is never heating up properly.
This is not good for your engine.

Buy yourself a thermostat. They are cheap and it is not a hard fix.

[Strat42586]

Thanks Doc. Much obliged for the recommendation. It's half-worked it's way out. it has never made it back down to the cold, and has pretty much stopped it's fluctuations. however, I do need to flush it anyways, so I'll change the thermostat when i do that.