Toyota Landcruiser HJ75 Series 2H - overheating when AC is on. Fixes?

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Toyota Landcruiser HJ75 Series 2H - overheating when AC is on. Fixes?

Unread post by Deno123 » March 1st, 2018, 4:55 pm

Hi all,
Just thought I would give this a shot as I'm running out of ideas.
I previously brought an old 75 series 1990 model that had no AC components as it was an option back in the day I was told; anyway, after a lot of searching and engineering I've got an AC system on it mostly genuine Toyota stuff and had it charged up with gas at our local guy. I went back today to check the head pressure of the AC and it was all good so he said, sitting around 250psi - 280psi on the high side and I think it was around 40psi on the low give or take.

Now the issue is that the ute starts to overheat when the AC is turned on. With the AC off the temp gauge will sit on the low end of half way at idle or running about all day, when the AC is turned on it will slowly creep up to just under the red or in the red, when I shut it down before it gets too high. It has not boiled over and I have checked the motor with a temp gun and its saying anywhere from 60 to 80-90 degrees.

This is what I have done and the issue is still ongoing.
-New Dayco viscos fan, it has had 2 tubes of oil put in it (as there was bugger all from the manufacturer) and I set the thermostat to around 90 degrees in it.
-The radiator in it is new ish, it was in it when I got it (not sure of the origin) and it is very clean
-The condenser is a genuine Toyota unit and it is also very clean and heat is distributed all over somewhat evenly so should not be blocked.
-Thermostat is new (aftermarket) and have taken it out and tested, it appears to be working opening at about 1/2 -3/4 of an inch.
- I have redirected the wiring harness for the temp and oil senders as they ran under the compressor on the hot side now they are over the top on the cold.
-Drained and flushed the radiator (its a 4 core) and put new heavy duty coolant in it. The core's appeared to be clean and freed of blockage.
- I'm confident the head and gasket are fine, I'm not loosing coolant and the oil is free of any milk contamination from coolant/oil cocktail.
-New (aftermarket) radiator cap and it appears to be working fine (holding pressure and what not).
-The temp sender is also new somewhat (aftermarket).

Any ideas boys would be great. Cheers Deno

Brett Mcleod
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Posts: 89
Joined: December 23rd, 2015, 8:30 pm

Re: Toyota Landcruiser HJ75 Series 2H (overheating when AC is on)

Unread post by Brett Mcleod » March 1st, 2018, 5:09 pm

probably better to ask this question on the 75 series owners page on facebook, lots of info & knowledgeable people with 75 series on there.
how did you come up with a 1990 model hj75, the last of the hj75 were made in 1989 & had the 2H, then from 1990 on they were a 4.2,
good luck, hope you can get it sorted.

Peter Aawen
Posts: 20778
Joined: June 17th, 2005, 8:01 pm

Re: Toyota Landcruiser HJ75 Series 2H - overheating when AC is on. Fixes?

Unread post by Peter Aawen » March 1st, 2018, 5:34 pm

^^Never hurts, but while you are here....

A/c units WILL require your system to get rid of A LOT of extra heat above & beyond what the motor normally puts out & what the stock cooling system is designed to handle, & generally, when installing them, even to new vehicles (few were actually 'factory') it often required all sorts upgrades including things like changing the viscous hub to one that started pulling air sooner; fitting a 'more aggressive' fan that pulled more air thru the rad; more efficiently sealing all the engine bay & grille/bonnet etc so that ALL the air flow HAD to be sucked thru the upgraded Radiator; sometimes even swapping the thermostat for a lower temp thermo that started opening earlier AND had a greater flow when fully open, and all sorts of other stuff.... and even then the temp gauges often made owners upset because they moved up and down in response to the actual temp changes, even tho the actual temp was still within the acceptable range, despite the gauge sometimes reaching the red!! So it wasn't surprising that many Dealers & eventually Toyota themselves added a resistor (or some other elec device) to the temp gauge circuit so that it didn't respond quite so quickly to changes the way it should.... and people got used to gauges that didn't reflect the reality of temp variations as cooling system loads changed!! When the reality of how engines & cooling systems is that if your temp gauge never moves, it's busted!! Engine & cooling system temperatures DO vary under load variations, and your gauge should reflect that of you risk it not warning you when things over-heat until it's too late!!

Still, if you have been checking your actual coolant temps & they aren't getting up over 100 deg C on the 'OUT' side of the engine & the 'IN' side of the radiator (actually they are usually good up to around 120 Deg C once the coolant is pressurised to about 8psi!) then there's a good chance that your cooling system is working fine & it's only the gauge & or sender making you worry - but remember, the needle on your gauge SHOULD go up and down as the cooling system load changes, anywhere from the Low mark right up to that little mark below the Red or H mark!! It's still OK if it's running just below the Red/H under full load, you just don't want it to get over that! Coolant temps of no more than 80-90 Deg C should mean your cooling system is fine..... ;)
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