12ht water temp

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Nov 9, 2009
Western Australia
hi guys just a quick question, done a search but found nothing. i have just installed a water temp gauge to my 12ht and am just wondering, what is the max temp i can hit and at what temp should i start to back off.
cherz jason
Hi Jason,

If your cooling system is in good condition, including the fan clutch working effectively, you shouldn't have any problems with overheating. The thermostat is 82*C if I recall, maybe 88*C.

I've never seen mine heading much north of the middle mark on the dashboard temperature gauge.

What temps are you seeing, and where is the pickup. Is it electric or copper cable temp gauge?

the gauge i bought is in F so it is normally around 180 most of the time. i have it plumed into the radiator top hose. i am just wondering when i should start to worry, i was driving up the big hill just out of Midland on Great Eastern hwy and they got up to around 200 maybe 210 cant quite remember, how ever on the stock gauge it got up to half.
just really wondering what tamps these engines can handle.

That's called Greenmount Hill Jason. With my gbentink turbo and intercooler, I can accelerate up there at 70km/hr and 80km/hr at any point. Coolant temp rises to the half way point and stays there. EGT are around 400°C pre turbo if I recall. Yes, it does make the engine work, but it's a sad excuse for a mountain in most parts of the world, or the east coast of Australia.

210°F = 98°C

100°C is boiling temperature of water under no pressure. Your radiator is under pressure created by the radiator cap, so this increases the boiling temperature to something higher - perhaps 120°C. There will be a chart somewhere. Check the pressure on your radiator cap and Google the new boiling temperature at this pressure.

Boiling coolant is bad as it creates overheating spots where the bubbles are. So the aim is to avoid boiling with good coolant and the appropriate radiator cap; it is not a matter so much of what the engine itself can take in the coolant area. Exhaust gas temperatures are far more important if the engine has been modified. With standard fuelling and turbo pressure there are no worries engine strain wise with a hill like Greenmount.

Some people, if they are keen, construct a steam bleed off the back of the engine where the coolant is always hottest. The steam bleed allows any steam bubbles to bleed off - which is why it is called a steam bleed. .... :doh: and allow coolant to clear the heat from the engine components as it is designed to do. The 12h-t in an HJ61 with a rear passenger heater already has a lovely steam bleed built in. The outlet for the rear heater is just where you would want to vent the steam, so if you're really concerned, you could open the rear heater tap and ensure any steam could vent away from the head.

If the standard dash gauge has gone up to the half way mark, that is all mine ever gets to. I imagine the thermostat is wide open and the radiator is doing what it is meant to do. If it rises above the half way point, then the engine is creating more heat than the radiator can clear and I would back off, and most likely stop and check for any leaks or signs of a problem.

I hope this helps you understand what is happening here. BTW, make sure you've plumbed in the temp gauge nice and securely; the things that break are often the things we add on, not the standard bits.

At http://tuning.mbs.id.au/Misc_Topics/cooling.htm I found
<for every one PSI the boiling point increases 3.25F / 1.8C>

Last edited:
thank you for the info Tim very helpful just what i was after, greatly appreciated.
cherz jason

Users who are viewing this thread

Top Bottom