Mechanical fan question

[Petescj]

Im confused a bit over my Cjs mechanical fan. My 81 has a clutch fan with 6 pitched blades on it. Technically the engine is from an 85. My recently purchased 82 has a fixed fan with 4 straight blades in an "X" pattern. I had another 82 before that used the clutch fan set up. What's going on? These examples are all AMC 258 i6 / 4.2l 's. Why the difference in cooling fans? What's the optimum running temp for the AMC 258 i6 / 4.2l and how do both of these fans achieve the same goal?

 

[elwood blues]

Standard vs Automatic? I do know there was a "heavy duty" cooling option at some point too, factory 3 row radiator. My '78 has a 6 blade flex fan, no clutch :dunno:

 

[mtnwhlr]

Both my '83 and '84 have the clutch fan I think they went to the clutch fan because they work more efficiently. From what I have seen all your newer stuff as the clutch fan or electric.

 

[Torxhead]

My '86 came with what is called a "Tempatrol" fan, which from what I gather is a fluid filled unit. I am not sure how they work or when AMC started using them. So if anybody knows anything about them let me know.

 

[Posi]

Jeep used two types of fans for the 6 and 8 cyl engines a fixed 4 and 7 blade. The 7 blade is the tempatrol which had a fluid coupling attaching the fan blade to the water pump. The fluid coupling is torque and temperature sensitive and automatically increases and decreases fan speed.

 

[Petescj]

Standard vs Automatic? I do know there was a "heavy duty" cooling option at some point too, factory 3 row radiator. My '78 has a 6 blade flex fan, no clutch :dunno:

The one with the 85 engine is auto. The two 82s both standard but one of each style

Both my '83 and '84 have the clutch fan I think they went to the clutch fan because they work more efficiently. From what I have seen all your newer stuff as the clutch fan or electric.

That seems to make sense , I was just wondering why the 82s were different.

My '86 came with what is called a "Tempatrol" fan, which from what I gather is a fluid filled unit. I am not sure how they work or when AMC started using them. So if anybody knows anything about them let me know.

That's what mine have. I had recently bought a new clutch for the one with the 85 engine.

Jeep used two types of fans for the 6 and 8 cyl engines a fixed 4 and 7 blade. The 7 blade is the tempatrol which had a fluid coupling attaching the fan blade to the water pump. The fluid coupling is torque and temperature sensitive and automatically increases and decreases fan speed.

Mine probably have 7 blades. I was going off memory while posting from bed. I'm guessing the change was made sometime during the 82 model year. Never knew the fluid was temperature sensitive. Wonder what it is and how long it actually works. I guess it has a higher viscosity at a higher temperature allowing it to spin the fan easier.

 

[Posi]

The 4 and 7 blade fan went back to the 70s, likewise with the tempatrol. The fluid is silicone. The bimetal thermostatic coil reacts to changing radiator air temps and regulates the flow of silicone into the drive chamber. The amount of fluid flowing into the chamber controls fan speed.

 

[Lumpy Grits]

My Ca. model '85 with trailer tow package, came with a 7 blade fan, 3 row radiator, fan clutch and shroud.
Mine runs it's best and 'cleanest'(smog)with a 195* t'stat. This was also OEM.
LG

 

[Posi]

how long it actually works.

To test,
warm up your engine
Slowly increase the rpms until you hear the fan slow down
Maintain the rpms until you hear the fan speed up
Your tempatrol is working as it should if the time interval between when you hear it slow down and speed up doesn't take longer then 3 mins.
If you use the throttle plate shaft to raise the rpms you can easily hear the speeds changes.

 

[Petescj]

The 4 and 7 blade fan went back to the 70s, likewise with the tempatrol. The fluid is silicone. The bimetal thermostatic coil reacts to changing radiator air temps and regulates the flow of silicone into the drive chamber. The amount of fluid flowing into the chamber controls fan speed.

Thanks. I never really knew how they worked.

My Ca. model '85 with trailer tow package, came with a 7 blade fan, 3 row radiator, fan clutch and shroud.
Mine runs it's best and 'cleanest'(smog)with a 195* t'stat. This was also OEM.
LG

Well this engine is from a 87 so I'll look for what was OEM that year as well. I'm using the clutch fan set up , a flow kooler water pump and a cheap replacement radiator that wasn't really cheap.

 

[Posi]

What's the optimum running temp for the AMC 258 i6 / 4.2l

There's far too many variables for a correct answer. What I can say is the factory spec 6 cyl thermostat opens at 205° and is fully open at 228°. The V8 opens at 195° and is fully open at 218°. I don't have a AMC 258 i6 / 4.2l so that's the best I have to offer.

If you had a V8 I could tell you I run 195°-200° on road with a cool day. The trail I'll see 220°. I'm going by my gauge on the trail and with a laptop logging engine conditions on road. (mechanical fan w/shroud Auto)

 

[elwood blues]

Lots of great info in this thread

 

[hole]

My 83 has the 4 blade fixed type on it, no shroud and a 195 stat and seems to run unbelievable cool. I can putt along in the desert for hours, get out and can hang onto the upper radiator hose bare handed. I started the practice because I was never sure I trusted the factory gauge as it always reads on the cool side.

 

[Lumpy Grits]

My 83 has the 4 blade fixed type on it, no shroud and a 195 stat and seems to run unbelievable cool. I can putt along in the desert for hours, get out and can hang onto the upper radiator hose bare handed. I started the practice because I was never sure I trusted the factory gauge as it always reads on the cool side.

That sounds like a stuck open t'stat. No way should you be able to hold the upper hose when at full temp.
LG

 

[Kane]

The important part (to me anyway) is the the clutch fan will not rob as much horsepower to operate and if you are crossing water it will stall the fan instead of smashing itself into the radiator if the water gets that high.

 

[hole]

That sounds like a stuck open t'stat. No way should you be able to hold the upper hose when at full temp.
LG

It's been like that as long as Ive owned it (08) Had to replace the water pump within a year of getting it and did the stat (180) along with it. Replaced the stat again less than 2 years ago when I did the 4.0 head , but this time put a 195 in it. Mind you , I cant hang onto the hose after a long highway speeds run, but low speed putting from place to place I can grab and hold on for 5-10 seconds without issue. Temp gauge never seemed to fluctuate and always read very low in the green, so I would periodically open the hood and see how hot the upper hose was. Redneck technology, but it works. Maybe 32+ years of concrete and framing have desensitized my hands some too

 

[Lumpy Grits]

If your temp gauge is electrical. Check the ground(GND)connections. It may well be miss-reading due to GND issues.
If the gauge is mechanical-Check to see if the sensor is correct to your gauge. A miss-match here, can cause a miss-reading of the gauge.

LG

 

[hole]

Electrical, and I'll check that