1990 F350 7.3 n/a overheating

Discussion in '6.9L IH & 7.3L IDI Diesels' started by zaroot, Jul 28, 2018.

  1. zaroot

    zaroot Registered User

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    1990 7.3 n/a 5spd 4x4 180k miles

    Correct Motorcraft thermostat, installed about a year ago.
    BB check valve in place. Clack clack.
    New Carquest water pump 2k miles ago, no leaks.
    Confirmed lower rad hose has spring intact.
    Confirmed upper rad hose is compressible.
    New 13psi radiator cap. Non lever locking style.
    Hose into overflow tank is good.
    No cracks in overflow tank, No leaks.
    Truck is stock fuel & stock timing.
    Can shine a flashlight through radiator, doesn’t appear to be clogged up externally.
    Looking under truck and around heads, no signs of cracks or coolant loss.
    Oil level is good, and no signs of coolant.
    Coolant is a little cloudy, but no signs or swirl or oil presence.

    Personally, I’ve never heard the fan clutch engage with the roar people explain. Shouldn’t be an issue when traveling 50-60mph though.
    Regardless, will be cleaning the bimetal coil and adding some silicone RC fluid to the housing to see if it makes a difference.

    Have tested the factory temp gauge by grounding out the wire. I also have a Bosch gauge on the pillar that is plumbed in at the factory location for the over temp sensor light. Towing about 8000 lbs up some decent grades in PA last week, it got hot. Highest was 240-245F, with outside air temps around 75. At the top of the climb, I pulled over, popped the hood, and let her idle. Came back down to around 210-215 within a few minutes of idling. At what temp do these things pop gaskets? If over temp light is set to come on at 242F, I was right in that zone for sure.

    Don’t really see much of a bleeder port for air burping. Truck used to tow this same route much cooler, old water pump bearing went out and starting dumping fluid (locally, not while towing), put on the new wp, New green coolant/distilled, SCAs, and last week was the first real long haul towing I’ve done since this work.

    Just fired it up cold with radiator cap on, and after idling 30-40 seconds there is a good amount of pressure when I loosen the cap. Idling at 190F and cap on, I don’t see any bubbles in the overflow tank from the black hose. Has some white smoke at startup when cold. Doesn’t smell sweet like coolant burning, but could just be masked by the cold diesel haze.

    The pics are driving it yesterday in 85-90F outside air temp, AC on, unloaded, 5th gear on a mild hill climb @65mph. Shouldn’t be getting to 215F unloaded, seems high when thermostat should be wide open @ 192F and also combined with interstate speed airflow across the rad.

    Bad head gasket? Exhaust gases pressurizing the cooling system? Air pockets? Anything else to check before I order a gasket kit and tear it down? Was planning a 12v swap in the spring and was going to gather parts this winter. Would really hate to sink the time and money into this ol boat Anchor. Great engine, just no power and mediocre mpg. Thanks!

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  2. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    Thank you for such a detailed post! At that mileage if the original fuel system has not been replaced then you are looking at a pretty tired IP and injectors, I would advance it a hair if they are original. Retarded timing can make for high egts which works your cooling system pretty hard. I would make sure the rad is blown out and free of dirt and debris. I don’t think you have an internal issue, you would know if the headgasket was leaking. How does the inside of the rad look? A coolant filter would be a great addition to the work you have done already. A good flush can really help these original rads to perform better, they get pretty built up with deposits over the years.
     
  3. zaroot

    zaroot Registered User

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    To elaborate, when I got the truck over a year ago, I advanced the timing a dimes width. I just it back to stock (I presume) 2 days ago, to see if the Advance was making it run hotter. Really made no difference.
     
  4. zaroot

    zaroot Registered User

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    If I am looking at a cooling issue, and also New Injectors and IP, that would definitely trigger a 12v swap for sure.
     
  5. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    Nothing wrong with that, the 5.9 is a good engine. Does your fan clutch have much resistance when spinning it by hand? If there’s any buildup on the coil then the clutch is bad. Fire the engine up and shut it off from the engine bay by pulling the front wire off the injection pump. Watch to see if the fan keeps spinning or if it stops with the engine, you very well may have a bad clutch. I usually replace them with the pump
     
  6. zaroot

    zaroot Registered User

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    I did the stick method with the engine running. It chopped it up quick. If I disconnect the IP front wire and am able to stop the fan, the clutch is bad? Does the engine need to be up to operating temp for the fan clutch to even try and engage for this test?
     
  7. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    If It keeps spinning when cold it’s bad
     
  8. zaroot

    zaroot Registered User

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    Fan has good resistance when cold. Once running, pulling the front wire on the shut down solenoid causes the fan to stop immediately. I believe Fan clutch to be working and operational
     
  9. zaroot

    zaroot Registered User

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    That still leaves me with getting hot at highway speed, and bubbling pressure in my rad (even just after start when cold). Anything else to check?

    I was simply going to add a little of the silicone fluid into the fan clutch to make it engage sooner. 240 is crazy late IMO.
     
    Last edited: Jul 28, 2018
  10. Runningaford

    Runningaford Registered User

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    I guess I've got bad hearing, I did replace my fan clutch, as the old one was definitely bad..... The new one, does lock up, but I can barely hear it when it does. To me, it sounds like an extra small little 'vroom', going down the road, and it does engage when not pulling, and sometimes only at around 60mph; Summertime I guess.
     
  11. The_Josh_Bear

    The_Josh_Bear Full Access Member

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    The way these engines "burp" air bubbles out after a coolant change is through that little check ball in the t stat housing neck. You mentioned it going clack clack in your first post, if that area was gummed up enough it might be preventing the air from purging out as quickly as you'd like.

    What's your coolant level now that you've driven it?

    The fact that it had good coolant temps before the WP switch tells me that you're fine and have air trapped or something else going on, at least much more likely than some sudden failure.

    240* is not going to blow a headgasket.

    Did you happen to test the t stat before you put it into the engine? Its cheap insurance and something I learned from forum guys. I haven't gotten a bad one yet in my vehicles but it keeps me from wondering and having to tear into the engine again just on a maybe.
     
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  12. saburai

    saburai Full Access Member

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    Honey? Honey, why are you cooking parts on the stove???:joker:
     
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  13. The_Josh_Bear

    The_Josh_Bear Full Access Member

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    Haha you freaked me out for a second, thought I accidentally called the OP Honey, lol.

    Not a T stat but a temp switch test, same idea. Dont forget to wash the pan real good.

    20180708_152656.jpg
     
  14. saburai

    saburai Full Access Member

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    It'll probably be better to have at least a dedicated pot, if not your own hot plate or burner. By the way, I have that same little multimeter! Great minds think alike...
     
  15. zaroot

    zaroot Registered User

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    Since the wp replacement, I have put about 1500mi & many many starts on truck; should have been enough to burp it out I’d think. Last weekend was the first time it’s really towed since wp, so that was the first real test. I think the hottest I got it on old wp was around 225-230. I agree, 245 isn’t nuclear; but it could still have popped the hg. What is the quickest/accurate test for hg status? I have a compression tester and gauge. Just worries me that there is some white smoke at startup, and the pressure into cooling system despite it being cold.

    I did not test the thermostat prior to installing, but I took a length test drive and couldn’t get it over 195F under load. At idling for 15 min, it sat right at 192F.

    Looks like a Mahle/VR upper end gasket kit, intake manifold gasket set, and new head bolts would be $250 shipped. Figure in getting the heads checked at machine shop and new coolant/oil and CDR valve would be under $450 all in.
     

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