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  1. WakeBoard&4X4er

    WakeBoard&4X4er 1/2 ton status

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    I have just bought a 1991 Blazer with 85K miles with the towing package. When I am driving at highway speeds and with the A/C my truck tend to get hot. The temp is about 230 (looking at the gauge it is between 210 and 260) @ 2100 RPM. If I turn the A/C off the temp will drop to under 210. I live in Kansas and drive in a rather hilly area and I have 33's on my Blazer and I tend to have my Blazer change gears for D to OD from time to time. My question is, is the high temp something to worry about? Will flushing the system fix the problem? Is it possible that my A/C unit is putting too much stress my engine? Thanks for all the help.

    Wake Board and 4X4ing it is ALL GOOD
     
  2. Boss

    Boss 1/2 ton status Author

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    I would flush it anyway. I don't have AC so I don't what temp it is suppose to run. But my K5 with brand new GM crate runs about 205-210max. When I break the engine in more, it should run a bit cooler. But since you said you just bought the truck, I would change all the fluids just to be safe and also flush your rad with Prestone super flush or something like it, you may see a bunch of rust chips draining out.
    Boss
     
  3. MudFrog

    MudFrog 1/2 ton status

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    Why not drop a lower temp thermostat in and see if that helps any.

    89 K5 Silverado
     
  4. Blazer1970

    Blazer1970 1/2 ton status

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    If you have 33s with stock gearing (3.42?), try driving in D instead of OD. The truck will drive a lot nicer, and it will stay cooler since the tranny will not get so hot (note that it is cooled by the radiator also). You will not likely experience a drop in mileage.

    Tim

    1970 Blazer CST 4X4 350 SM465 NP205
    1987 Suburban 4X4 350
    1988 Chevy Pickup 4X4 350
     
  5. Fast

    Fast Registered Member

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    I just went thru that with my 84.The thing that made the biggest different was that I changed the stock 5 blade fan foe a 6 blade unit from Summit, then added Redline water wetter. Like others have said you you may want the flush the sysytem and have the radiator checked for blockage first. These changes were a lot less expensive than the brand new 3 row radiator I put it and had zero effect on the heating problem.

    Fast 84 K5
     
  6. MudFrog

    MudFrog 1/2 ton status

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    The tranny will run cooler but the engine will run hotter if you switch to D instead of OD. With the larger tires, and that gearing your RPM's will remain pretty low when driving in OD.

    89 K5 Silverado
     
  7. Nate87k5

    Nate87k5 Registered Member

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    Since you have a 91 you will get up to the 200 to 210 range because most of them came from the factory with a 195 temp thermostat because of the computer. I had the same problem with my 87. It was getting up to 210-220 with the A/C going and outside temp about 110. I changed out the thermostat three days ago to a 180 and I haven't had it go over 190 after it has warmed up and cruising for 20 miles. I would flush out your system and then replace the thermostat. I would also recommend an outside trans cooler if you are running alot of mountains. I would not recommend going below a 180 thermostat unless you have a performance chip and it calls for one.
     
  8. ken

    ken 1/2 ton status

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    I have a stock '90 Suburban 4x4 (California) with the 5.7L TBI motor and have had a 160 degree thermo in it for almost 200,000 miles. When it had lower mileage on it, it would get up to 15 MPGs on the highway...so don't let anyone tell you that the lower thermo will screw up the mixture, or computer or anything...IT WON'T, I am proof of that!!! Nothing like an icey cool engine!!!

    ken
     
  9. WakeBoard&4X4er

    WakeBoard&4X4er 1/2 ton status

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    Do any of you all think that it is beacuse my A/C could be going out? The A/C works Great (I think), it is cood and runs me out of the truck to warm up!!!
    Thanks for all the help!!!

    Wakeboarder&4X4er
     
  10. dumbfounded

    dumbfounded 1/2 ton status

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    Naturally it's going to run hotter with the A/C on b/c you are now heating up the air before it goes through the radiator. 230 is a little hot but not detrimental to the engine. The tranny won't last as long at that temp so invest in a tranny cooler. Flush the sys change thermostats maybe a new water pump they aren't expensive. Over heating can be caused by so many things so try one thing at a time, but I'd invest the few dollars for a tranny cooler.

    Love, Peace, and Hair Grease...........
     

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