chasing the last few degrees of coolant temp.

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rc51kid

rc51kid

Joined
May 31, 2010
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I have a 1994 fzj80. Runs perfect and is 100% baselined. Even by mud standards. Coolant system is all OEM and new inducing radiator, hoses, water pump, thermostat, heater valve, OEM black fan clutch with 10,000 oil.

Also complete top end rebuild with all new OEM gaskets and head gasket and a lot more.

I run 188-198 normally. Sits mostly around 194. I did get warm on a HOT dry day climbing LOOOONG switchbacks off road with NO AIR FLOW last summer on Morrison Jeep Trail, 219 degrees. It dropped fast once i put it in neutral and idled it up to about 2000 rpm. Temps are coming from a Koso mounted in the coolant hose.

I see a lot of people running 188 ALL DAY! Any chance i could get there or should i be happy with what i have? I could put 12000 or 15,000 in the fan clutch. Or i could replace the black with a blue and replace oil as most people do.

I could replace the fan clutch but i hear the black are better than than the blue anyway. Should i call it good and be happy with what i have or should i venture on for the elusive last few degrees?

PS on a side note. Only "issue" i ever have is slightly inconsistent idle speed. I figure my air idle controller is not 100%. Some times it is a little low at 500-600 RPM. Could it just be that my idle a little low? But i also see 194ish on the highway some times.
 
I'd say that your cooling system sounds good. If you want more air flow while slow driving and idling off-road consider an electric pusher fan.
 
Weld the fan clutch?
 
Our mods and engine rebuilds are almost the exact same except I didn't go oem with new rad, and didn't change fan clutch.
My Koso guage also hit 219ish twice this summer on long mountain passes. I am a little lower then yours normally but I wouldn't think you have any issues. Guage is sure to be +/- a few degrees anyway.
Sure is nice to watch that guage go down and everything work as it should isn't it. I get a warm fuzzy feeling when I see the temp drop as i crest the hill and go down the other side.
 
So here is my thoughts on this.

I have a 93, fully rebuilt 4.6 with a new Koyo 1918 radiator, blue fan clutch with 10,000 cst oil and the timing is just slightly advanced. Temps are measured with a koso gauge in the output hose.

I hold 176-186 on most drives. NOW I have noticed that on long drives up grades (from Grand junction to vail pass, this is bout 160 miles of gradual climbing) that my temps stay below 186 until I get to Avon. This is where the grade steepens and my temps shot up gradually to about 206. I pulled off in vail and noticed that my fan wasn't really moving air.

This climb from Grand Junction to vail just happens to be where I cooked my head gasket as well.

I know on the fan clutch mod threads there is talk about how advancing the fan clutch timing may cause the oil to heat up to a point which it loses its shear capacity. In this case thats what I suspected. Thinking that some residual moab juice was coating the radiator fins I turned my water pump on and hosed off the radiator and fan clutch.

Then I went up vail pass (2,500' elevation gain in a short distance), I had my foot to the floor and I didn't see temps exceed 186. Did cooling the clutch down 'reset' the fluid or was it just hosing down the radiator... Idk but I suspect its the wimpy blue fan clutch.

Yea I know everyone says its totally fine and it probably is but I never see temps above 190 when driving around the front range, its only on super long trips with pass climbs near the end. I've been thinking of pursuing electric fan set up with shroud to replace the mechanical fan.
 
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I have also experienced high temperatures on the harder climbs. Weston pass and some random mountain down in Arkansas. Both of which required me to drop the TC to low gear in order to summit. Sometimes the temps would get up to 220's. Its really not a big deal. I figure if jeep designed the old inline 6 to operate at 215-220 all day everyday then its probably not going to hurt the 1FZ to occasionally get up there.
 
Perhaps 219 degrees is a number that the Koso gauge likes to display? I installed a
Koso last spring when I did a complete cooling system overhaul on my 93. I saw 219 cruising at 70mph with AC on in 100 degree ambient temp.
Before that is saw 214 climbing Donor Summit on I80 in 85 degree ambient temps.
Another time
Inwas ascending a fairly steep, curvy mountain trail with AC on (wife's request) at about 10mph in about 85-90 ambient temps and the AC cut off. This was prior to having the Koso gauge installed. I stopped and checked temps with my infrared thermometer and sure enough, the water outlet was 226 degrees. This all happened with a black hub clutch containing 12,000 cst oil and set to open at 100 F. I have and electric pusher fan waiting to go in.
It looks like your rig is normal @rc51kid
 
Plug in a scan tool and see what it says instead.
 
My LC 80 thread. has some interesting info and stats, posts about the fan install start at around # 178, plenty to read up on so get a coffee first. I do use an electric fan but put that aside for the moment, for whatever reason the 80 cooling system when on the move around 75 MPH and above OR/AND under load for considerable time climbing a long hill for example absolutely, definitely, without a shadow of a doubt, MUST have the sponge 'fillets' in place around the radiator!

Testing shows they are worth a reduction of at least 5 degrees C @ 80 MPH in 40 degree C ambient temperatures, there is also a plate across the chassis in the steering damper area, that seems to help as well? Why I do not know, it is behind the radiator, perhaps there is some weird aerodynamics going on?

Also make sure you do not have large obstructions in front of the rad, a pair of spotlights for example.

regards

Dave
 
Dave 2000 said:
My LC 80 thread. has some interesting info and stats, posts about the fan install start at around # 178, plenty to read up on so get a coffee first. I do use an electric fan but put that aside for the moment, for whatever reason the 80 cooling system when on the move around 75 MPH and above OR/AND under load for considerable time climbing a long hill for example absolutely, definitely, without a shadow of a doubt, MUST have the sponge 'fillets' in place around the radiator!

Testing shows they are worth a reduction of at least 5 degrees C @ 80 MPH in 40 degree C ambient temperatures, there is also a plate across the chassis in the steering damper area, that seems to help as well? Why I do not know, it is behind the radiator, perhaps there is some weird aerodynamics going on?

Also make sure you do not have large obstructions in front of the rad, a pair of spotlights for example.

regards

Dave
Click to expand...
Please elaborate on the foam "fillets". I have read stories about these but neither of my 80's have them. Do you have a part number? Where, exactly, are they fitted?
 
baldilocks said:
Please elaborate on the foam "fillets". I have read stories about these but neither of my 80's have them. Do you have a part number? Where, exactly, are they fitted?
Click to expand...

They are in the most basic form strips of foam rubber/heavy sponge, they are packed around the borders of the radiator. The idea is that as much air as possible is forced through the radiator matrix, with the gaps around the edges the airflow can escape and does nothing to aid cooling. I have no idea of the part numbers but, anything you can mould to fit in there will be fine. I used polystyrene strips, easy to cut and wedge in place and water/rot proof to boot.

Ultimately I will use rubber flaps from body to radiator edges, will be more effective and look neater.

regards

Dave
 
The biggest impact on my temp's is when I blend down to a 30/70 or 20/80 coolant/distilled water mix for the summers. The results are pretty drastic when you bump up the H2O percentage and add a water wetter.
 
Winter where I live on the coast is rarely below 4 degrees C however, yesterday it was 10 on the coast and a 30 minute drive inland over the mountains and we were at -4 C and in snow. Further north would have seen cooler temps, so a 50/50 for my location is fine, I do not use any other additive such as corrosion inhibitors/water wetter.

Meant to add, the antifreeze here is already mixed with distilled water, you simply purchase 10, 30 or 50 % mix.

IIRC I used 30% once when testing different fan switches, did not seem to alter overall running temps but would have course altered the boiling point.

regards

Dave
 
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