Hello Mel.
Doesn’t sound good.
It seems you are trying to tell whether you have an overheating problem or a headgasket problem (or both, ouch).
When doing the work to date was the system flushed out? What was the state of the coolant? As I’m sure you know the Hiace has a fairly complicated and compromised system that has to be kept in tip top condition. It might be worth taking a look at my fairly long post on cooling in my Show Us Yours section. It’s below the bit on the rear drums.
While you’ve done a lot of work this will be compromised if the system wasn’t flushed really, really well and the coolant isn’t in tip top condition. Junk in the system can re-block a new component such as a radiator / front or rear heater matrix which will cause problems. It’s also difficult to properly flush the engine block.
A couple of things spring to mind.
The 1KZ engines have a lower temp thermostat, 71C rather than 88C. Was the right one fitted? Is it still fine? They generally do work well and last a long time.
It’s possible to fit a radiator cap with a higher pressure rating. This wouldn’t be my first option as it could cause a leak elsewhere. Is the system leaking past the radiator cap and not getting up to pressure so boiling off before it should? A clean of the crustiness might help it seal properly if that’s the case.
How is the fan clutch? These are meant to be able to spin easily at low temp but lock up at the higher end of the operating range to drive more air. When they fail they tend to lock at lower temp and slip at operating temp. There are loads of YT vids on these, including re-oiling, but they aren’t massively expensive. It’s also possible to fit a fan with different temperature profile, but I don’t have all the numbers. You’d likely need to speak to AISIN. A fan with an earlier lock up will also rob a bit more power.
There’s also a 10 bladed fan rather than the original one with 7 blades. It’s an OE Toyota part, which was fitted to several cars and vans. It’ll pull more air but that’s not necessarily a proper fix.
Is the replacement radiator up to task? How is the temp gauge? Any air locks?
Water pump could be the problem, but you’ll only know by getting in there. You can diagnose their pumping by disconnecting the belt and seeing if you can push water around, but I doubt that will be definitive. The pump isn’t a massively expensive part to replace but needs quite a bit of teardown and best done as part of a timing best swap. It could be gummed up but this is getting into the problem of engine flushing. The expansion tank might also give you an indication to the condition of the system.
I think one of the best tests for headgasket failure is to test for combustion gasses in the coolant. This is a fairly simple test, but it might not be completely definitive for a failure if the gasses are not going into the coolant. If you have combustion gasses in the coolant then it’s a probable for a headgasket.
Final points to think about are to consider whether you’re blocking air flow with bars, lights etc. Is the radiator full of grass?
How’s the intercooler. I don’t have one of these on my van and know nothing about them in this application.
What was the train of event to lead to this?
Sorry to not be more helpful. I’d be temped to flush the system really well (see my post), fill with new coolant and test that for combustion gasses in the coolant. If present then it’s almost certainly a headgasket. If none present then the other areas of the cooling (fan, thermostat, pump) might be the issue?
HTH!!
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Sun Oct 29, 2023 8:53 am
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