Thermostat choice

I’m doing a coolant flush soon and will hange the thermostat water pump and some hoses as preventative maintenance. It looks like there are 2 different thermostats 88c and82c. Anyone have opinion on which one to choose and why?  Thanks

Hello Merlin

Been wondering this, too.

As an opener you might like to read the long post I’ve put here on cooling:

https://hiace-super-custom.forumotion.com/t4317-my-lh119

Not teaching you to suck eggs of course, but I’ve gone into the cooling system pretty fully and this post also shows where I flushed my heaters etc. You need to scroll down below the pictures of the rear brakes. On the flushing pictures, there, the green braided hoses were freshwater ones, but I did this both ways. Hope it helps. Also, in the future I will add a drain tap somewhere along the low point of the rear heater loop as this doesn't drain properly. You can see this and it's sort-of implied in the 'drain and refill' v 'fill from empty' volumes for vehicles with rear heaters, which is ~2L more.

I also think you are spot on to carry out preventative maintenance on the cooling system. There have been a few posts in recent times on cooling and it seems to be a fairly common thread, which was part of my thinking for my post, which isn’t finished yet btw.

Here's a photo of the thermostat from my 3L-engined van:


The device is in a bag, in a box, on a shelf in another room so no disassembly required. Mine is a ‘MotoRad’ make and is stamped 88C (192F) in its cup.

I’ve no idea how original this is (suitability for Japanese, UK or anywhere else env temp range for example) or if there is a better variant out there (faster opening etc) but when I took it out I did test it, using the ‘pan of water on cooker with thermocouple’ method and it worked fine. I also don’t know whether vehicles that are used for towing etc would benefit from a different opening temperature.

Hiace southeast:

https://www.hiacesoutheast.com/store/cooling-system

list 3 thermostats but don’t mention what the operating temperature on their 3L variant is. You could ask, I suppose, but you can see their others are 82C or even 71C so I’d guess their 3L is 88C.

The best fit repair manual I have for my van (RM156) doesn’t sadly have a ‘co’ or coolant chapter and the ones I have that do have a ‘co’ chapter are for the 1RZ and 2RZ engines these use a 82C thermostat.

For my LH119 van the Electronic Parts Catalogue recommends two thermostats and both are for 88C, see:

https://toyota.epc-data.com/regius_ace/lh119v/114894/engine/1603/16331A/

You should probably tailor this to yours and see if it’s different.

The last thing to mention is whether a lower operating thermostat temperature might give a degree of safety against overheating or whether a lower temperature might have other consequences; is over-cooling a thing? I don’t know.

Cheers!