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Subject: spoke to soon

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lonestarjeff    Posted 08-08-2018 at 23:01:23 [URL] [DELETE]        [Reply] [Email]  
  • spoke to soon
  • Coming back from my daughter's house yesterday afternoon the needle started climbing again. It was right at 100 degrees outside & I was rolling around 75-80mph when it crept up just enough to cause the A/C to shut off. Then the needle would start slowly dropping until it fell back to normal operating temp & the A/C would kick back on. Then the same cycle would start again.

    Once I got to my exit & was driving around town the gauge stayed in the normal range. After pulling in the driveway after the "episode" I checked the usual points...hot pressurized upper hose, warm lower hose, overflow tank at normal level, no leaks. Today, all was normal driving around locally.

    Can't figure out what in the world could be causing this that I haven't already replaced. Highway speed overheating would be radiator or pump or temporary pressure loss. Maybe the engine is running too lean? Can't imagine how the computer would let that happen, unless one of the sensors is fooling it, but I'm not getting any codes.

    Mower    Posted 08-12-2018 at 14:23:37 [URL] [DELETE]        [Reply] [No Email]  
  • Re: spoke to soon
  • You have a slight head gasket leak. High speeds/ac/trailering build higher pressures in the engine, the heat opens the gasket slightly, and you're getting hot gasses directly into the coolant. A block tester will confirm the gasses in the coolant.

    It's not unusual for the 4.6 of that vintage.

    lonestarjeff    Posted 08-13-2018 at 21:53:30 [URL] [DELETE]        [Reply] [Email]  
  • Re: spoke to soon
  • Picked up a block tester kit today. Testing tomorrow.

    dave#1    Posted 08-10-2018 at 13:22:49 [URL] [DELETE]        [Reply] [No Email]  
  • Re: spoke to soon
  • Try a new fan clutch . Possible that at high speeds on a very hot day with the AC on that a worn clutch can't quite keep up cooing the radiator.

    lonestarjeff    Posted 08-10-2018 at 18:43:55 [URL] [DELETE]        [Reply] [Email]  
  • Re: spoke to soon
  • I did change the clutch back when this started, but I may change it again anyway. The old clutch felt like it was still good to me, but this is the 1st time I changed one.

    Bruce(OR)    Posted 08-09-2018 at 12:45:09 [URL] [DELETE]        [Reply] [No Email]  
  • Re: spoke to soon
  • Ha ha. . . . I might have figured it out for you. How about a missing air dam that is air flow that should be directed through the radiator being allowed to now go another direction? Missing/dented air dam under the front bumper? in front of, and below the radiator? Sides of the radiator?

    lonestarjeff    Posted 08-10-2018 at 00:06:10 [URL] [DELETE]        [Reply] [Email]  
  • Re: spoke to soon
  • All the original air channeling parts still there. Wish I could find something like that to solve the mystery. :-(

    Bruce Dorsi    Posted 08-09-2018 at 08:00:40 [URL] [DELETE]        [Reply] [No Email]  
  • Re: spoke to soon
  • I read you changed the pump, radiator, thermostat, & hoses. ...Not much left to change!

    Any possibility the coolant temperature sensor has gone bad and needs replacement?

    Highway speed overheating can also be caused by insufficient airflow thru the radiator or retarded ignition timing. ....The computer should be controlling the timing, but do you have anything mounted on the front which could disrupt or impede airflow?

    Engine compartments being as crowded as they are, sometimes restrict airflow from LEAVING the compartment at high vehicle speeds. ....Have any air dams or spoilers been added or removed from the front end to change airflows?

    lonestarjeff    Posted 08-09-2018 at 08:37:08 [URL] [DELETE]        [Reply] [Email]  
  • Re: spoke to soon
  • Nothing mounted or changed front or back of the radiator, of course the A/C condenser has its share of bug impacts, etc.

    It just seems like poor air flow would be a bigger issue at low speed(ie. a bad fan or plastic bag)where highway speed would compensate the problem. I thought about the sensor/sender, but I think when they fail its kind of all or nothing. It seems like more of a coolant flow restriction problem, but all I can think of to cause it is the :-(stat. What are the odds of installing 3 bad :-(stats in a row?

    steveVa    Posted 08-10-2018 at 09:09:29 [URL] [DELETE]        [Reply] [No Email]  
  • Re: spoke to soon
  • I had a boat motor once that kept overheating at medium speed. I replaced the t-stats twice and it still did the same thing. I then realized that the new t-stats were just a little different then the original ones. I had also replaced the water pump so there was not much left to try. I ended up drilling holes in the new t-stats to allow more water to flow thru at low speeds and at low temps. This fixed the issue.

    lonestarjeff    Posted 08-10-2018 at 18:38:12 [URL] [DELETE]        [Reply] [Email]  
  • Re: spoke to soon
  • If I can't come up with any other solution, I'll probably change the t-stat again!

    steveVa    Posted 08-10-2018 at 22:19:40 [URL] [DELETE]        [Reply] [No Email]  
  • Re: spoke to soon
  • It may not hurt to try one with a slightly lower opening temp.

    lonestarjeff    Posted 08-13-2018 at 21:55:42 [URL] [DELETE]        [Reply] [Email]  
  • Re: spoke to soon
  • If my block test comes up negative I will likely try another t-stat.

    Walt/Tx    Posted 08-09-2018 at 18:37:07 [URL] [DELETE]        [Reply] [No Email]  
  • Re: spoke to soon
  • Letís assume temp sensor and stat and timing all good......maybe restricted exhaust like in the cat converter? I canít think of anything else, sorry for your troubles on a good old truck.

    lonestarjeff    Posted 08-10-2018 at 00:10:14 [URL] [DELETE]        [Reply] [Email]  
  • Re: spoke to soon
  • The truck sounds the same. Not sure what other signs point to a clogged cat(other than red hot). Have to get out the temperature gun.

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