Speaking as an owner of three Renix XJ's, I suppose I should get round to writing that cooling article I've been composing for the last couple years or so...
Here's some thought to help you -
1) Run 180* thermostat. It's doesn't do anything for cooling directly, but will get your coolant flowing earlier and will complement a few other things that can be done.
2) When you install ANY thermostat, drill two 1/16" holes in the flange, as close to the edges as you can get (I come in a little over 1/4" on all of mine.) When you mount the thermostat, make sure the holes are at 6:00 and 12:00 installed location. Why? The Renix system is known for trapping air behind the thermostat, and the bleed holes will make the system constantly self-purging for air. The controlled weep also seems to help in general, but I don't remember why and I don't feel like working it out right now...
3) Make sure the lower radiator hose has a support coil (looks like a big coil spring) in it. Under suction, that hose can collapse when warm, and cause trouble for you.
4) De-crap your cooling system. As little as 1/14" of scale is a 10% drop in efficiency, and it's not a linear increase. When you refill, use distilled or R/O filtered water ONLY. Keep some in the garage at all times. Not even spring water - distilled or R/O ONLY. (R/O = Reverse Osmosis)
5) Check your fan clutch. Average life of the thermal clutch is 3-5 years. To test, get the engine to operating temperature, turn off, and try to turn the fan by hand. There should be significant resistance - if not, it's shot. Replace.
6) De-crap the radiator fins as well. While you have the fan out for clutch replacement, blow the radiator out from the engine side with a fine stream of water. Use a decent flashlight from the back to check when you're done. Repeat as necessary.
7) Water Wetter. Great stuff.
8) If the radiator is still OEM, replace it. It's pretty well shot by now, and the Renix radiators from the factory weren't that great. I have a high-efficiency Modine 3-core that I got locally, you shouldn't have any trouble finding one.
9) The pipe nipple for the heater hose on the water pump uses a standard pipe thread - 3/8"NPT I think. I replaced mine with a pipe stub and elbow, so the hose bend was gone. I'm working on a similar setup for all over - brass tubing with rubber vibration stubs at all terminii. Why? Better coolant flow and less rubber to wear out - and the pipes themselves will conduct heat away from the coolant. Every little bit helps.
10) I've heard from a lot of people running adjustable MAP sensors - as the mix gets rich, the operating temperature drops. Makes sense - the additional fuel in the mix acts as a coolant, absorbing heat as it is vapourised. Something else to consider - the mod itself is fairly cheap. It's on my own "to do" list.
11) Automatic transmission? External cooler! If you can, get the kit with the thermal control valve and divorce the transmission cooler entirely - that will get a hot oil circuit out of your engine cooling. This will result in a significant drop in operating temperature and cruise.
12) An engine oil cooler won't go amiss, either. Oil gets everywhere, and would you rather pump hot oil or cool oil thru your engine? I know the answer, so do you.
Of course, this isn't everything, just what's off the top of my head. I've dropped operating temperature on my 88/5sp to about 185-190*, and my wife's 89/AW4 to about 190-195*. If one of us hits 210*, I want to know why.
It's been said that the hotter-running 4.0 was meant to help with emissions control (reduced HC and CO,) but I've not noticed a problem here - Santa Clara County wants biennial sniffer checks, we've just gone to Smog Check II (dyno test) - and our emissions levels are so low they aren't tested, they send in miners to dig for them....
All this with stock fans. Getting the 4.0 cooler isn't a matter of moving more air - it's a matter of moving more HEAT. Moving more air won't help with that, until the system moves more heat into contact with the air. Believe me, you're moving plenty of air up there!
5-90
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