Expert Advice needed; Piston noise

[AmbroseEmmanuel]

Couple of things.
No thermostat tells me she’s been run hot previously and someone has removed the thermostat hoping this will miraculously fix the problem.
Not going to happen. Thermostat is there to maintain engine coolant temp. If the engine runs too hot even with the thermostat wide open, you have to find the problem.
Usual culprit with a KZ is cracked cylinder head, often in the exhaust port area so you don’t see coolant in your oil or vice versa. Engine just overheats as coolant is boiled out the exhaust.
Why do they crack heads? Sure Toyota heads have a weakness but with the age of these cars you have to look at the viscous coupling on the fan.
Unless the fan locks up to max as coolant temp rises, the engine will just get hotter and pretty soon it’s all over.
If you do some searches you’ll see how to add silicone oil to the hub which can repair an old unit.
Easy fix is to buy a new hub, either genuine ($$$$) or aftermarket.
To test the hub start the car from cold and rev her to about 2000rpm. You’ll hear the fan roaring but after a very short time, that roar noise will subside as the hub starts to slip.
You need to hear that roaring noise when the car is working hard, otherwise the fan is simply not doing its job.
You’ll get used to hearing the fan cycle in/out as it cools the radiator.

thank you so much for the detailed explanations. so the final verdict on my engine after discussing with multiple experts here in the country is that I'm gonna put a new engine in the car. and by new i mean the used engines that were used in japan low mileage ones but sealed and imported in pakistan. we can't get the brand new engine here. these used engines are usually in pretty great nick. so that's what i'm thinking to do next month.

[carco]

Couple of things.
No thermostat tells me she’s been run hot previously and someone has removed the thermostat hoping this will miraculously fix the problem.
Not going to happen. Thermostat is there to maintain engine coolant temp. If the engine runs too hot even with the thermostat wide open, you have to find the problem.
Usual culprit with a KZ is cracked cylinder head, often in the exhaust port area so you don’t see coolant in your oil or vice versa. Engine just overheats as coolant is boiled out the exhaust.
Why do they crack heads? Sure Toyota heads have a weakness but with the age of these cars you have to look at the viscous coupling on the fan.
Unless the fan locks up to max as coolant temp rises, the engine will just get hotter and pretty soon it’s all over.
If you do some searches you’ll see how to add silicone oil to the hub which can repair an old unit.
Easy fix is to buy a new hub, either genuine ($$$$) or aftermarket.
To test the hub start the car from cold and rev her to about 2000rpm. You’ll hear the fan roaring but after a very short time, that roar noise will subside as the hub starts to slip.
You need to hear that roaring noise when the car is working hard, otherwise the fan is simply not doing its job.
You’ll get used to hearing the fan cycle in/out as it cools the radiator.

[AmbroseEmmanuel]

So i found out that the thermostat valve was taken out by the previous owner's mechanic. The radiator isnt in a bad condition but probably would be worth replacing too. I had recently got it cleaned and had put in the original toyota coolant

[carco]

Sounds like she’s been cooked. New head won’t fix a cooked bottom end, rings will have lost tension and pistons may have worn skirts causing the slap your mechanic is hearing. An engine rebuild or replacement is probably needed but first you have to find why she overheated or it’s going to do it again.

[AmbroseEmmanuel]

Hi guys. This is the first time I'm posting in this forum although when i bought my 90 series, I have obtained lots of helpful info from this forum. I own a 1996 prado tz with 1kz-te engine. The engine was overhauled in March by the previous owner. I bought the vehicle in April. I've been very satisfied with the vehicle. I live in Pakistan in the north and while going towards the east on the motorway with both A/Cs on, the car heated up despite the temp gauge needle being in the middle. The Ac stopped working, the coolant evaporated and the engine oil needed to be replaced too. Meanwhile since then the piston noise is there as the mechanics told me. I need opinion about what could be the best option. Some people have suggested me to change the head assembly only as that would fix it and others have advised me to change the engine as the engine has been previously overhauled. I can put up a video here if needed. Would appreciate comments and opinions on this post.

Regards
Ambrose
Pakistan