cooling system issue with very high km-age 1hz in my hzj80

[sunrk]

I noticed the engine temp monitor that I use for coolant temp monitoring has been showing ordinary driving temps a bit higher (in the 80 to 85 c range) than the standard 75 to 78 c and it's been happening over a few weeks consistently.

I investigated somewhat a few days ago one morning when the engine was fully cold. Did not find any evidence of coolant leaks but I did find the coolant overflow bottle almost totally full and the top section of the radiator was not full of coolant up to the cap like it's supposed to be.

I put the extra coolant in the overflow bottle back into the radiator proper to restore the fluid level.

Since then the same behaviour is showing up. I did the usual checks of oil (in case of a possible head gasket leak of coolant to the oil passages) and nothing. There's no obvious tell-tale of a head gasket leak the other way (oil to the coolant system).

I'm curious what's going on. The radiator is not particularly old (it was a brand new genuine Toyota one I fitted in 2017), and the water pump and t/stat were both done when I last did the timing belt job within the last 12 months.

I've had the radiator cap fail once before and the current one is an aftermarket item.

Could the cooling system be over-pressurising somehow causing excess fluid into the overflow but it not coming back as the engine cools after shutting off? Or could it be an issue with the radiator cap again? Is there any kind of valve in the cap of the coolant overflow bottle?

Note this it with a 1hz engine (original to the vehicle) that is now sitting at almost 729 k km's on the odometer. The vehicle is basically due for it's next oil and coolant system changes which will include a proper flush of both those systems (and new oil filter and maybe t-stat).

Thanks, Craig.

 

[robnicko]

when you poured the fluid back into the radiator from the overflow was the remaining level in the overflow then at its normal cold level? This will indicate if its being consumed internally
Id get a genuine cap for starters. It could just be (hopefully) the valve in the cap failing and not sucking the coolant back when cold / holding correct pressure when hot
If you do the TStat, genuine again

 

[sunrk]

Yes I only returned what was above the mid-point leaving the overflow fluid level where it normally would be. I only ever use genuine t-stats. The current cap is an after market. Going to get genuine's of both because the vehicle is due for it's coolant and oil changes so doing t-stat at same time is simple.

There's no evidence of coolant leaks anywhere but if the overflow bottle gets too full I guess it will overflow out of the overflow if that makes sense.