Outer Limits 4x4 Board

My Hilux has started to run at 70c where it used to be around 80 - 90c.
I checked the thermostat and found that it's stuck open. Is it a problem to run it at 70c? I imagine the thermostat is set to open in the 80s for a reason - can anyone shed any light on why I'd want it to run at 80 - 90?

not the best to run them cold. use more fuel and increase wear. especially as stick open thermostat will make the warm up take a very long time.

70 degrees isn't too bad. If it was dropping right down when you did long downhill runs (no fuel being injected) then you might have a problem with engine wear and heater efficiency.

3L thermostats are about 30 bucks for a genuine. May as well fix it for that price.

wish i could get mine to run that cool. mine sitsd on 90 and i hate it.

since your going to change it get one of the highflow thermostats. available in 88c and 82c.

tweak'e wrote:since your going to change it get one of the highflow thermostats. available in 88c and 82c.

Yeah I looked for the Tridon high flow but couldn't find one without ordering it in.
I ended up putting a standard flow 88c one in yesterday and now it runs at 90c (as I would expect with an 88c thermostat).
If Toyota intended the engine to run at 90c, and based on the earlier commenst about operating temp, I am happy with that.

One thing I did notice whey doing this was that my coolant seemed to have a small amount of brown / gray sludge in it. I assume this is oil that has gotten into the coolant - is a small amount usual / expected or is any amount a bad sign? I flushed and replaced the coolant when I did the thermostat.
I also pressurised the cooling system and noticed that it dropped pressure over a 10min period - no leaks externally so it must be an internal leak.
From what I read it could be a sign of a bad head gasket or maybe a leak in the oil cooler.
Next step I plan is to do a compression test to see what that shows - anything else I should be considering?

Sounds like it could be a slight leak from the head gasket, or oil cooler? Somewhere the water can come in contact with the oil if a gasket was to fail.

Compression test will confirm if it's the head gasket.