1HZ (HZJ80) Temperature Gauge and Thermostat

[SilentForever]

Hello! I have a 1995 Land Cruiser HZJ80 with a manual with only 105000km. I have recently flushed the entire cooling system and put in Toyota Red, I have also changed the radiator cap (Denso), upper and lower radiator hoses (oem toyota), Aisin water pump.

I have also replaced the water temperature gauge sender(oem toyota) and the connector. I have also replaced the thermostat to the oem toyota 76c (90916-03089) which starts opening at 76c and fully open at 90c.

What I noticed is the temperature gauge sits very low, barely 1/4 and quickly drops to cold when driving at higher speeds such as highway. (See attached photo) I have check the ground at the sender and it pegs all the way to hot when grounded. Battery terminals are also brand new. I also tighten and check for corrosion for the ground screw nuts behind the gauge and they are tight.

So I went to an automotive electrical shop expert and they said it is the the thermostat opening too early which explains the drop the temperature at higher speeds. So I put in a oem toyota thermostat with the same size and diameter which is rated at 82c. (90916-03100) which starts opening at 82c and fully open at 95c. After I change the thermostat to the 82c the temperature sits at 1/3 and does not drop at higher speeds anymore. (See attached photo)

I know the oem temperature is by no means the most accurate gauge but I could use some insights and opinions on this. I would really appreciate it if any of you with a 1hz show me where your gauge sit when fully warmup and what thermostat are u using. This vehicle is operated in a tropical climate with 32-35c ambient temp during the day and 24-29c during the night. Thanks! PS. The rpm gauge is sourced from a 1hdt because my old one is broken.

 

[nick_the_fish]

Hi SF and welcome to the forum.

I have a 1HZ in my 105 series. My temp gauge reaches the halfway mark after a couple of minutes of running and sits at half and never fluctuates. It has a Toyota thermostat in it (part number 90916-03089) which I think opens at 76 deg C. I note that you have a turbo gauge on your dash - and to be honest I didn't know that the 1HZ came out of the factory with a turbo. I thought they were an aftermarket think on the 1HZ.

Mine is a non-turbo 1HZ, so by the sounds of it takes a different thermostat.

Hope that helps

N

 

[SilentForever]

Hi SF and welcome to the forum.

I have a 1HZ in my 105 series. My temp gauge reaches the halfway mark after a couple of minutes of running and sits at half and never fluctuates. It has a Toyota thermostat in it (part number 90916-03089) which I think opens at 76 deg C. I note that you have a turbo gauge on your dash - and to be honest I didn't know that the 1HZ came out of the factory with a turbo. I thought they were an aftermarket think on the 1HZ.

Mine is a non-turbo 1HZ, so by the sounds of it takes a different thermostat.

Hope that helps

N

Thanks for the reply. Mine is also a 1HZ non turbo but it is an 80 series. The rpm gauge is sourced from a 1hdt as the original one is broken and does go past 2k rpm