1998 hzj75 overheating????

[toy88]

My cruiser has started overheating under load! It's a 1hz diesel, while driving around town it's fine, then as soon as you start going over 60kph it starts getting hot, the aircon trips out & the temp sky rockets!!
It has a brand new thermostat, new radiator, new hoses & water pump is 10000km old, there's no sign of water in the oil or oil in the coolant, there's no sign of exhaust gases leaking into the coolant no bubbles etc!!!

So please someone help me figure this out because I really want to go fishing next week

 

[ForealBoreal]

Thermostat installed wrong?

 

[Gun Runner 5]

Are you confident the temp. gauge is functioning properly?

 

[hzj79lee]

If u r ascending long hill, it will overheat. 1hz is underpower for climbing

 

[Aussie 25]

have you tried the viscos coupling on the fan, when the motor gets hot 3/4 on gauge pop the bonnet and put your thong agenst the back of the fan and push, if it stops easy that is your problem. 1 you get a new coupling. 2 go to toyota and buy a tube of silcome and put it in.

 

[toy88]

Thermostat can only go in one way, so yes it's in correctly.
Temp gauge is accurate, coolant overflows when hot n spills all over the ground.
It's not the fan because it cools down at idle! It only gets hot when on the highway at speed or under load. & there's no hills where I live

 

[sadam_husain]

if you've replaced the radiator, thermostat, waterpump and hoses and checked the fans operating correctly then its time to take the head off and get it inspected and tested, was the radiator etc replaced because of overheating or was it cooling ok at that time?

 

[toy88]

I replaced the radiator because I damaged it, it was cooling fine up until a week ago, I have checked it with a TQ tester, & that came up fine, I have a funny feeling it's something simple (I hope) I'm not in the mood to be taking my head off

 

[toy88]

I had replaced the radiator because I damaged it, been cooling great up until a week ago, I have TQ tested it, I was trying to avoid taking the head off

 

[roscoFJ73]

I had replaced the radiator because I damaged it, been cooling great up until a week ago, I have TQ tested it, I was trying to avoid taking the head off

I would pull the t/stat out and check it.Was it a oem T/stat? I often use aftermarket parts but I always use the OEM T/stat on advice from someone who rebuilds 1HZ for a living.

I would also remove the upre radiator hose and watch the coolant flow while dribbling water into the radiator .
If not the T/stat,maybe a blockage in the block.

Im not convinced its a head problem either,the 1HZ dont usually have head problems unless there is some catastrophic failure elsewhere,eg blown lower radiator hose.

Did you add a new radiator cap,always a good thing to do 1st.

Unmodified 1HZs rarely have overheating issues unless you drive above 120-130kph on warm days or in sandy conditions with 40psi in your tyres.

 

[buschmaster86]

i flushed th cooling system of my 3b there cam alot of brown rusty crud out.

so i let the radiotor be seviced by a specialized company.

also other thermostat and gauge/sensor is worth the try (new 1hz is verry expensive) and would be a waste of a beatifull piece of engine

 

[toy88]

The thermostat was an oem one, it's working fine, coolant is flowing freely throughout the system, it is a new radiator cap along with radiator, I have TQ tested it & there is no gasses in the the cooling system, so not a head problem, so I'm seriously thinking maybe it's a viscous coupling?? But you would think that would affect it more at slow speed not high speed with cool air flowing through the radiator? What are your opinions? Cheers

 

[Radd Cruisers]

No, the viscous coupling very much affects higher speed cooling.

It is a common myth that vehicle speed will provide enough air flow through the radiator to cool an engine running at highway speeds. A properly working viscous coupler is key to proper cooling system operation. Note that a fan shroud must also be in place for the engine fan to cool properly.

The other thing to look at is the water pump, I have seen a few cases where the impeller separates from the shaft and will not provide substantial water flow through the cooling system. I have seen this exact scenario play out on an HDJ81 recently - and the water pump had been replaced on it only a few thousand Kms before this happened. A new pump solved the problem.



~John