View Full Version : FJ60 runs hot with A/C on - where to start?

08-07-2007, 12:07 PM
So...the FJ60 is running hot with the A/C on. the temp climbs to above the 3/4 mark, but not much higher. I cannot notice the fan-clutch engaged. if I turn off the A/C and drive a little, the temp gradually lowers and eventually, I can start hearing the clutch engaging slowly at first then more 'robust' as things cool down - almost like when it's that hot, it's not on, and as it cools, it starts to lock up more and more until it cools and the temp guage down to about 1/4 or less. I almost feel like in non-A/C driving the fan-clutch kicks on more often than I'm used to.

everything is 'normal' without A/C on. That is, it runs a little cool (1/4 or less on the guage, and fan clutch engages quite often).

Also, A/C blows pretty darn cold when on, RPMS go up to about 1100 when comp. kicks on.

I'm totally stumped - not sure where to start. is the fluid in the clutch just getting worn or something??

08-07-2007, 12:26 PM
Do me a favor, just check your coolant level. I'm only saying that since I was almost ready to dive into a more complicated shakedown process when my coolant was a little low and the engine was getting hot, so I want to make sure that's the first thing out of my mouth.

Don't know much about the fan clutch, but I suppose it's possible, but it kinda sounds like radiator too - with the rad. sitting behind the a/c condensor, the delta T goes down when you're running the a/c, and the flow could be restricted enough to prevent sufficient heat transfer from the radiator under that extra heat load.

08-07-2007, 12:32 PM
coolant level seems perfect - overflow bottle at the high side of high/low...but ya'know...I haven't cracked the rad. cap yet. the Rad was new about 5 years ago and I changed fluid once or twice since then.

here's what's interesting...for years, when I have heat 'on', the temp rises slightly to about 1/3 up the guage. when the heat is off... the temp settles to about 1/4. Seems opposite to me. :confused:

Can you explain more about the Delta-T...(?) I kinda get it, but not really.

08-07-2007, 12:38 PM
Temperature difference. The greater the difference, the more heat transfer. Fancy way of saying your AC condenser is adding a bunch of hot air.

Your fan clutch sounds suspect, and yeah, they do wear out/fluid breaks down. Can never hurt to chemically clean your radiator as well! And of course, fresh coolant can save a headgasket near you!

08-07-2007, 12:50 PM
I think if you use fancy words like delta you should have to use the ∆ symbol.. :) ∆=change.

08-07-2007, 12:51 PM
well I'm not a computer geek so I don't know how to make any fancy "delta" symbol. :tongue2: :D

Shawn - your condenser will "steal" some of the cold air that would otherwise be used to cool your engine coolant, so if your radiator is in good shape then you need to pull more air across it - that's where your fan comes into play. If it's not engaging and pulling air, then you might get the symptoms you are seeing.

I bet you're wishing everything was just air-cooled like a good 'ol VW aren't you? ;)

08-07-2007, 01:02 PM
:thumb: I bet you're wishing everything was just air-cooled like a good 'ol VW aren't you? ;)

HAH! you said it! they are ALOT more simple!

things are starting to make more sense...thanks! I'm thinking the fan clutch is on its way out, or at least the fluid is breaking down. is there a specific temp range for that fluid to replace in the clutch?

08-07-2007, 02:26 PM
I'm thinking the fan clutch is on its way out, or at least the fluid is breaking down. is there a specific temp range for that fluid to replace in the clutch?


Are the FJ60 fan clutches "serviceable"? I'm pretty sure the older 80 series fan clutches aren't (well, not in theory) and therefore everyone has been going to a new fancy "blue hub" version. Basically from what I've seen is most state if the fan clutch is original (on the 80 series) it needs to be replaced. The new blue hub version IS serviceable in that you can change out the silicon fluid to a differect cst (??), change the temp at which the fan will kick on, etc.

I know we're talking 60 vs 80 series here but maybe the fan clutches are similar. If interested there is a thread on MUD by Landtank on modding the blue hub fan clutch. He describes how to change the temp at which the fan will come on and also about changing out the fluid. I think they come with 4000cst fluid and some swap to 6000cst or even 10000cst fluid. You can get the fluid at hobby stores. I bought some 6000cst (IIRC) from CDan with my new blue hub fan but haven't (and probably won't) end up using it.

08-07-2007, 04:13 PM
Another way to test your fan clutch (perhaps a redneck way) is to drive on the highway under the same overheat conditions. If the truck does not overheat, then this lends credibility to the fan clutch not working, rather than the radiator being clogged. The fan is there to move engine through your radiator when the truck is not moving fast enough to move its own air. If the truck overheats worse on the freeway, it points to (but doesn't conclude) that the radiator is mostly plugged.