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Unread 09-16-2011, 07:18 AM   #1
bamasteeler
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Running hotter on highway

Round town the cj runs usually about mid range on factory gauge. Get up on highway and within few minutes cruising at about 55-60 my temp indicates upper range of gauge. I'm thinking waterpump isn't able to circulate coolant efficiently at higher rpm's. At first I thought maybe t-stat not opening enough but think that would be evident even around town driving. My plan is to change both t-stat and water pump if I go to change anything since I am in that area. Was wondering if anyone else ran into this issue and maybe what it was on your cj. Thanks

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Unread 09-16-2011, 07:31 AM   #2
lucdog
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Is there a spring in the bottom radiator hose, it could be colasping at sustained higher RPM's. I think I'd check first.

Bill
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Unread 09-16-2011, 08:04 AM   #3
Foundrydude
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Collapsing hose is a good thing to check for, and if it's got a fixed fan instead of a clutch the fan may be blocking airflow.

If you got a dirt track racer buddy helping tune it and locked out the mechanical advance and vacuum advance, that'll cause highway heatup too! So be sure it's not stuck from corrosion either.

good luck!
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Unread 09-16-2011, 08:12 AM   #4
jblue1555
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If your still running hot after all that take the rad to a shop and have them flow check it or pull the tanks and rod it out. Running hot at highway speeds usualy is due to low flow.
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Unread 09-16-2011, 10:58 AM   #5
bamasteeler
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Quote:
Originally Posted by lucdog
Is there a spring in the bottom radiator hose, it could be colasping at sustained higher RPM's. I think I'd check first.

Bill
Yes it is a reinforced hose, a gaites flexible hose that is very stiff not the 5 dollar one from parts store lol believe the spring is made into the hose and surrounded by the rubber
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Unread 09-16-2011, 11:01 AM   #6
bamasteeler
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Quote:
Originally Posted by Foundrydude
Collapsing hose is a good thing to check for, and if it's got a fixed fan instead of a clutch the fan may be blocking airflow.

If you got a dirt track racer buddy helping tune it and locked out the mechanical advance and vacuum advance, that'll cause highway heatup too! So be sure it's not stuck from corrosion either.

good luck!
Yes the fan is fixed no clutch on this.
What are you suggesting I check to see if it's stuck from corrosion??
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Unread 09-16-2011, 11:43 AM   #7
Bakunin
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nah

Quote:
Originally Posted by bamasteeler View Post
Yes the fan is fixed no clutch on this.
What are you suggesting I check to see if it's stuck from corrosion??

The clutch fans disengage at speed, so they aren't taking HP and only spin at the rate of airflow coming through your radiator.
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Unread 09-16-2011, 11:50 AM   #8
bamasteeler
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Quote:
Originally Posted by Bakunin

The clutch fans disengage at speed, so they aren't taking HP and only spin at the rate of airflow coming through your radiator.
Yeah I don't have a clutch fan type, got a straight fan
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Unread 09-16-2011, 12:12 PM   #9
aero mech
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I suffered from the same problem after the last rebuild. i replaced my two core with a three core for a cj with a 304 from autozone. problem solved. jc
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Unread 09-16-2011, 12:13 PM   #10
lucdog
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Quote:
Originally Posted by bamasteeler View Post
Yes the fan is fixed no clutch on this.
What are you suggesting I check to see if it's stuck from corrosion??
Inside the distributor, the advance mechanicals.

Bill
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1957 WILLYS pickup, needs work.
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac trail Jeep.
1979 J20
1980 CJ5 trail Jeep.
1983 CJ7 pretty weekend and sometimes to work Driver in the summer, My first rebuild, if the Q-trac and 5 are broke, this one is the one to take. its just as capable as the other 2, except nice paint.
1984 Grand Wagoneer, 1 ton axles, great 360/727, and a big a$& tree fell on it .
1989 YJ the CJ to YJ conversion.
2005 TJ Rubicon.
2011 Grand Cherokee Laredo 4x4, Mrs. LUCDOG's DD.
Lots of parts not for sale, i'm a hoarder.
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Unread 09-16-2011, 01:59 PM   #11
SleeperCJ
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I had the same problem on my 258 after it was rebuilt. I never dealt with it though since I didn't drive it on the highway much and have since swapped motors and radiators. The cause I suspect was that with the motor rebuild there was less slop between the pistons and cylinder was so the friction at higher sustained rpm caused more heat. If your pump is not malfunctioning you may need to employ some other means to increase cooling, bigger radiator, remote oil cooler, loovers to increase air flow out
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Unread 09-16-2011, 08:01 PM   #12
twmattox
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How confident are you in a 30-year old gauge? I would at least get an IR thermometer and do some checking of the thermostat housing. I know on one of my other Jeeps, factory gauge showed an 80* temperature swing when the actual temp went from 190 to 205...
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Unread 09-18-2011, 12:53 PM   #13
Foundrydude
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Fixed fan will block airflow on a vehicle with lots of grille area at highway speed. Most people think the disengagement is just for power/mileage but when the air is already moving 60mph a fixed fan will slow it down if you've got oversize tires or an overdrive transmission to slow the engine speed. Vehicles with fixed fans are designed to run 3000rpm and up on the highway. If you've modernized to a point it's turning a sane RPM at highway speed then the fan should be modernized too.

Be double sure the distributor advance is not sticking before spending money chasing overheating.

good luck
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Unread 09-18-2011, 03:16 PM   #14
Max-Q
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Your fixed fan is causing the airflow to slow at highway speeds. As the guy above said, say your motor is only turning 2,000 rpms on the highway. The airflow at say 70 mph is greater than the pull of the fan blades at that point. The fan is now creating a barrier which is blocking the higher velocity air from flowing across the radiator.

You need to get a fan clutch.
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Unread 09-18-2011, 04:49 PM   #15
foggybottombob
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Quote:
Originally Posted by Max-Q View Post
Your fixed fan is causing the airflow to slow at highway speeds. As the guy above said, say your motor is only turning 2,000 rpms on the highway. The airflow at say 70 mph is greater than the pull of the fan blades at that point. The fan is now creating a barrier which is blocking the higher velocity air from flowing across the radiator.

You need to get a fan clutch.
I'm not buying this at all.

When you are driving at speed, the fan can be not turning at all, turning slow, turning 2 times slow or turning really fast and the air flow change through the radiator will be negligible. I have an electric 2 speed fan that I can turn on hi, low or off and it makes no difference in coolant temp when you are driving fast. The no clutch fan will add a little more drag on your engine at high rpm but I would guess that factor is less than 5 horsepower.

Now if you are getting detonation (pinging) your engine will definitely heat up really fast at high speed. You might try some higher octane gas for a tank.
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