Truck overheats at highway speed but not in town

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  • FSJ Guy
    • Mar 20, 2005
    • 10061

    #16
    Put a fan shroud in. The cooling "system" needs all parts of the system installed in order to work correctly.

    Let us know what happens.
    Ethan Brady
    1987 Grand Wagoneer, slightly longer than stock.

    www.bigscaryjeep.com

    Don't mess with me. I once killed a living hinge.

    Comment

    • backpack09
      327 Rambler
      • Nov 09, 2005
      • 568

      #17
      When was the last time you adjusted your carb? If you are running lean, you can quickly build up some heat at highway temps.

      Also, have you checked and rechecked for any leaks in the system and also bled the system with the nose up in the air?
      Dan G
      91 GrandWag
      MSD Mag Dizzy, MSD 6A

      Comment

      • tgreese
        • May 29, 2003
        • 11682

        #18
        Originally posted by jpcoutts
        Your post says you have a stock 360 but doesn't mention whether or not it has been rebuilt. 360's can't handle much of an over bore. The thin cylinder walls inhibit heat transfer to the rest of the block if bored too much. A fan shroud would be a good place to start I think.
        I don't think that's true, at least when compared to say a 304 or other 'conventional' engines from the era. Certainly the 401 can overheat if overbored more than, say 40 thou. However, the bore size of the 401 approaches the maximum bore spacing for the AMC block, making the as-cast cylinder walls thinner.
        Tim Reese
        Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps.
        Browless and proud: '82 J20 360/T18/NP208/3.73, Destination ATs, 7600 GVWR
        Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
        GTI without the badges: '95 VW Golf Sport 2000cc 2D
        ECO Green: '15 FCA Jeep Cherokee KL Trailhawk

        Comment

        • d4xycrq
          232 I6
          • Aug 17, 2006
          • 25

          #19
          What are your RPMs at highway speed?

          Do you know what your RPMs are at highway speed? You could be flirting with redline if you are in the 4s' (4.10:1, 4.30:1) I have an early Bronco that does exactly what your truck is doing. It has 4.10s, and I suspect the valves are not staying closed long enough to bleed off the heat! (at that high RPM...)

          Meanwhile, I have a J-Truck as well. It overheats at highway speeds, too! But the big 'ole snow plow in front is the culprit!

          Ray

          Comment


          • #20
            I remember a clutch going bad on a Merc I had................replaced the clutch and it would do exactly what yours is doing. I could drive around the city all day long never a problem. Get it out on the highway and kick it, would not take long I was on the side of the road.............waiting for it to cool down. After many frustrating hours of trying to figure out what was wrong........................Turned out I had put the fan on backwards when I changed the clutch, so I had turned it into a pusher fan on the wrong side of the rad
            Daily Driver 2008 Wrangler Sahara
            Going, Gone, or Thinking Fishing

            Comment

            • Don S
              • Feb 06, 2002
              • 5613

              #21
              ..
              rreed;

              Sorry to hear of the problem...
              ... My 401 isover bored .030 and runs very cool. The radiator is the one that was in it when I bought it over twenty years ago. I did add a home made shroud and an air dam. Check out the articles in the link below to solve the problem. It worked for me... If it works for you please pass the link to others that need it.

              FUEL & COOLING

              ... I did notice that when driven (a test) ten miles or more at 60 MPH in second gear (TH-400) on a 95 degree day, that temperature would rise to about 200 degrees. At constant 75 MPH (in 3rd gear ) on a 100 degree day the 401 runs at the temperature of the 180 degree thermostat.

              Have a good one while you can still laugh about it.. Don S..
              If something I’ve posted on the Internet offends you please ignore it.
              If you don’t know how to ignore something on the Internet e-mail me … and I’ll demonstrate.
              Sold our 1976 Wagoneer 406, MC4300, TH400, QT, TruTrac, 2" lift, 31x10.50s, duel Optimas,
              It?s took us over 161 Colorado Mountain Passes, 3 Jeep Jamboree USAs & 2 Ouray Invasions from 1985 to 2010
              ACRONYMS & ABBREVIATIONS HERE

              Comment

              • letank
                AMC 4 OH! 1
                • Jun 03, 2002
                • 4124

                #22
                Originally posted by Tripwire
                Could the lower rad hose be collapsing at higher RPM's? that is the "suction" side of the pump and the lower hose should have a big coil spring inside it to prevent it from collapsing.

                Trip
                My first idea too. If you are missing the inside spring.

                Otherwise you stated mix 70/30, i hope it is 70 water, 30 coolant, if it is the reverse... 70 coolant and 30 water, then you will boil over.
                Michel
                74 wag, 349Kmiles on original ticker/trany, except for the rust. Will it make it to the next get together without a rebuilt? Status: needs a new body.
                85 Gwag, 229 Kmiles. $250 FSJ test lab since 02, that refuses to give up but still leaks.

                Comment

                • rreed
                  350 Buick
                  • Aug 21, 2006
                  • 1472

                  #23
                  Somehow my post from last night isn't here today..

                  Engine has 20,400 original miles, it was taken out of a J20 air force ambulance. It has not been rebuilt or otherwise bored over. HEI/e-coil hybrid ignition, dialed in timing. Edelflood carb does need some work as I have the gasket kit laying on the bench; accelerator pump is out but we're talking cruising speeds of ~65 anyway, not during quick acceleration. It smells stinky so I don't think it's running lean but who knows. Vacuum is a good ~18" at idle.

                  Lower hose does have the spring in it, I transferred over when swapping in new hoses at the engine swap. Radiator is clean inside and out as you can see through it into the engine bay in daylight. Had the radiator flushed while it was out recently. Ran straight water through the truck for a few days (flushed and repeated a couple times) to flush junk out of the system. Dumped it and filled w/ fresh 70 antifreeze/30 distilled water. The end of my driveway is an incline, I filled there, ran it sans cap until the t-stat opened, topped off. I do not believe it has any air but will double-check.

                  When swapping the fan clutch I had both laying face down on the bench, transferred fan directly but will check. I would think around town would have overheated w/ a backwards fan but will check. I'm not sure what to make of the fan clutch; the original stock (20,400 mi.) clutch would provide little resistance when hot, but the new Hayden feels no different at all. I got a cheapy HD cooling clutch from Vatozone for my ZJ and at hot it's very difficult to turn. I don't believe I've ever heard the fan in the truck at any temp. I'm considering taking it back and picking up the same cheapy Vatozone one for my truck since I know it stiffens up at temp.

                  I do have a little bit of antifreeze pooling up at 1-2 of the intake manifold bolts but just barely enough to touch the bottom of the bolts, and this is over a few weeks and 2-3 overheats. I do plan to pull those bolts, clean out the holes as best I can, coat the bolt in ultra black RTV, see if that works. I wouldn't consider these 1-2 bolt puddles "leaks.."

                  This truck is not lifted, all bone stock minus ignition upgrades, Edelbrock adapted to intake manifold, true dual exhaust (no cats, flows freely). Front bumper is homemade 2x4" c-channel w/ diamond plate atop, there is no airdam or shroud. Tags on the diffs say 3.73, I'm running 265/75-16 tires (~32"), T-18 trans. At 65 the rpms are around 2800-2900 or so, pretty high actually. I did the math and thought 3.73/32" would run around 2500 rpms at 65 but may need to recheck. Or the tags are wrong and it's 4.10. Anything faster than 65 and it gets scary anyway.

                  That link is awesome, I'll try some of those things. Could I get some pics of some airdams? Do they connect to the stock bumper (since I don't have a stock bumper)?
                  47 Willys
                  75 CJ-5
                  81 Scrambler
                  76/79/80/81/85 J20 (all the same truck)
                  86 Grand Wagoneer - FOR SALE!!!
                  96 ZJ

                  Member, FSJ Prissy Restoration Association

                  You can't drink all day if you don't start in the morning.

                  Comment

                  • Tripwire
                    AMC 4 OH! 1
                    • Jul 30, 2000
                    • 4656

                    #24
                    Hmmm...Dunno,

                    An interesting observation about my cooling issue - could be related or not.

                    My OEM Radiator always kept my temp in the normal range no matter what conditions...eventually it died of old age and i got the El-supremo-cheapo-Bast@rd one from Shucks...Ever since then it suffers more or less the same problem you have.

                    I have replaced it TWICE with the same PN and the issue persists. After talking to the manager today ( this time the rad failed because the mounting Tabs are all seperated from the core) He said there is a Heavy duty version they have that cools better - even though it has fewer rows as the cheapo model.

                    It's a couple bucks more...but WTF....Perhaps this is your problem? a cheapo radiator?

                    Trip
                    Abort? Retry? Ignore? >

                    86 GrandWag. Howell fuel Injected 360. MSD Ignition + Dizzy. 727/229 swap BJ's 2" Lift and 31's

                    88 Wrangler 4.2, Howell TBI and MSD - Borla Headers w/ Cat-back + winch and 31's AND a M416 trailer (-:

                    Comment

                    • letank
                      AMC 4 OH! 1
                      • Jun 03, 2002
                      • 4124

                      #25
                      Originally posted by rreed
                      Somehow my post from last night isn't here today..

                      it and filled w/ fresh 70 antifreeze/30 distilled water. The end of my driveway is an incline,

                      this is part of your problem..... 70% antifreeze is way too much antifreeze.....

                      Drain 1 gallon.... and replace w distilled water. If you have a testing tool for antifreeze concentration, it will give you a better idea of the mix, but coolant must be cold to measure concentration.

                      years ago.... i did the mistake of using pure coolant (the previous brand that i got was premixed) .... 100% coolant will boil over very fast.... at freeway speed.... took me about 5 miles to get there....
                      Michel
                      74 wag, 349Kmiles on original ticker/trany, except for the rust. Will it make it to the next get together without a rebuilt? Status: needs a new body.
                      85 Gwag, 229 Kmiles. $250 FSJ test lab since 02, that refuses to give up but still leaks.

                      Comment

                      • mud crawler
                        232 I6
                        • May 16, 2006
                        • 55

                        #26
                        Originally posted by Crazy_Jeepman
                        I remember a clutch going bad on a Merc I had................replaced the clutch and it would do exactly what yours is doing. I could drive around the city all day long never a problem. Get it out on the highway and kick it, would not take long I was on the side of the road.............waiting for it to cool down. After many frustrating hours of trying to figure out what was wrong........................Turned out I had put the fan on backwards when I changed the clutch, so I had turned it into a pusher fan on the wrong side of the rad
                        I had the same problem ...with the fan clutch ...it was shot ...same story around town not a problem it was ok hit 65 - 70 it went into the red line. Rule of thumb mark one fan blade with chalk. Start your engine ...and then turn it off if your fan spins more than 3 revolutions " i believe this is the figure "...it is shot the clutch is not holding it . Which means that the higher the RPM the fan slips and doesn't do it's job . I replaced mine with a GM / delo unit

                        Comment

                        • pb
                          350 Buick
                          • Aug 28, 2003
                          • 1443

                          #27
                          Originally posted by letank
                          this is part of your problem..... 70% antifreeze is way too much antifreeze.....

                          Drain 1 gallon.... and replace w distilled water. If you have a testing tool for antifreeze concentration, it will give you a better idea of the mix, but coolant must be cold to measure concentration.

                          years ago.... i did the mistake of using pure coolant (the previous brand that i got was premixed) .... 100% coolant will boil over very fast.... at freeway speed.... took me about 5 miles to get there....
                          What he said. More water, less antifreeze.
                          Paul
                          1975 Wagoneer DD
                          360 with large cap ecm controlled HEI, TBI EFI, Comp Cam 260H, Edelbrock Performer Intake, CS130 alt, 4 row radiator, S10 steering box, QT w/LO, WT 3.54 D44 axles. Rancho 9000X's, ~4" lift, Caddy rear discs.

                          Comment

                          • aerocorey
                            304 AMC
                            • Oct 14, 2006
                            • 2034

                            #28
                            I think anything you can guess might be causing your problem is a waste of time until you get a fan shroud in there.
                            Corey

                            Current
                            87 GW "Big Bear"
                            76 J20 project "Ox"
                            90 GW parts rig "Velma"
                            77 J10 parts rig "NoMo" (as in "no more Jeeps, Corey!")
                            94 YJ "Coop"

                            Past
                            88 GW "Hercules" (had to sell in '08, curious who has it now)
                            83 Wag parts rig "Shaggy" (used to build Herc, then scrapped)
                            73 J4000 (had to sell due to PCS in '07)
                            75 Cherokee "Jerry Lee" (sold in '13 because I'm an idiot)
                            74 Cherokee "Dino" (used to build Jerry Lee, then scrapped)

                            Comment

                            • cgs0409
                              232 I6
                              • Jun 10, 2001
                              • 73

                              #29
                              Originally posted by Tripwire
                              Could the lower rad hose be collapsing at higher RPM's? that is the "suction" side of the pump and the lower hose should have a big coil spring inside it to prevent it from collapsing.

                              Trip
                              Thelma Lou is overheating as well. I installed a new 3 row radiator, new water pump, and new hoses. The thermostat was replaced last year. I didn't think to remove the coiled wire in the lower hose and install it in the new hose and I think it's collapsing. Does anyone know where I can get the coiled wire for the lower hose...mine went in the trash dump? I'm going to replace the thermostat and see if that helps. What it does is run past half way on the gauge while driving...sometimes it goes higher. Then after the engine is cut off for a while it will peg the needle when you crank it back up. After you drive it a ways it will cools back down... .
                              Charley...

                              1976 J10 (Thelma Lou 360 3spd)
                              1978 Cherokee S (Hurley Hog 360 4spd)
                              1970 Commando V6 3spd
                              1976 CJ5 (Fire Stomper 304)
                              19?? CJ3B (Ole Yeller OHV4)
                              1943 Navy, flat 4

                              Comment

                              • The PIG Smith
                                King Browless

                                Moderator
                                • Nov 30, 2001
                                • 6537

                                #30
                                Originally posted by letank
                                this is part of your problem..... 70% antifreeze is way too much antifreeze.....

                                Drain 1 gallon.... and replace w distilled water. If you have a testing tool for antifreeze concentration, it will give you a better idea of the mix, but coolant must be cold to measure concentration.

                                years ago.... i did the mistake of using pure coolant (the previous brand that i got was premixed) .... 100% coolant will boil over very fast.... at freeway speed.... took me about 5 miles to get there....
                                I second this!
                                I had some overheating issues with my J20.
                                When I installed the carb/intake, I failed to put in the proper mixture.
                                I replaced the Rad Cap and now have a 50/50 mix, tested with a hydrometer.
                                With a 16# cap, my coolant is good up to about 260-270 degrees.
                                My mechanical gauge stays around 210 degrees.
                                Bryan Smith
                                2017 Jeep Grand Cherokee Limited
                                - 75th Anniversary Edition - 1941 Trim Package - Recon Green
                                1986 Jeep J20
                                - Super clean rig from the AZ/CA state line
                                1982 Jeep J10
                                - Has become a Long Term Project.
                                1981 Jeep J20
                                - Commercial flat bed - Lost in a Divorce --gone
                                1987 Jeep J20 Pioneer
                                - Former Rick Bielec aka Ricbee plow rig. Major rust!! --gone

                                IFSJA Member #1933 Joined November 30, 2001

                                Originally posted by Jayrodoh
                                ...but if it works, I wouldn't touch it.
                                Originally posted by Lindel
                                Best laid plans, yada yada yada...

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