1992 4.9 Coolant Mystery
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HT4100 4.1, 4.5, 4.9 Discussion, 1992 4.9 Coolant Mystery in Cadillac Engine Technical Discussion; Hello, I recently purchased a 1992 Coupe Deville w/84Kmiles. I drove the car back from where I bought it approx ...
  1. #1
    BlackLac96's Avatar
    BlackLac96 is offline Cadillac Owners Member
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    1992 4.9 Coolant Mystery

    Hello,
    I recently purchased a 1992 Coupe Deville w/84Kmiles. I drove the car back from where I bought it approx 1hr drive back in Nov and noticed there was not any heat (this was a tough drive back). The car sat all winter and when I got it out to look it over I decided to change the coolant as I had no idea when it had ever been done. Prior to this I noticed the expansion tank was gurgling up when the car was shut off. I filled the coolant in the radiator and ran it a little more to temperature and the expansion tank was rising but did not run over. After I talked to my mechanic he said the thermostat may be faulty or the radiator restricted. I replaced the radiator and thermostat and completely flushed the entire system (even back flushed the heatercore) when I started the car to fill the coolant as the manual states to do w/the rad. cap off it started gurgling out the radiator neck as the car idled. I let it sit and cool off and refilled the radiator. Started up later and let it get to idle w/the cap on and the expansion tank began to fill up. When I turned the cap to let pressure out a lot of air and coolant rushed back into the expansion tank. There is also no heat...the heater hose that connects to the t is hot coming to the heater core and back down to the water pump but is cool on the restricted side of the T as well. What the heck is going on here? ANy help will be GREATLY appreciated!

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    Ranger's Avatar
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    Re: 1992 4.9 Coolant Mystery

    Sounds a lot like a blown head gasket is pumping exhaust gases into the cooling system. When it's cooled down, remove the cap and smell the tank. Smell like exhaust?

  4. #3
    BlackLac96's Avatar
    BlackLac96 is offline Cadillac Owners Member
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    Re: 1992 4.9 Coolant Mystery

    Ranger,
    Yes it does. I'm pretty bummed because I was thinking that might be what it is and I've owned many of these engines, one with over 240K original miles and never had this problem. I guess I got a lemon.

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    MrDobin is offline Cadillac Owners Fanatic
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    Re: 1992 4.9 Coolant Mystery

    240k? Good god, well done on that.

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    Ranger's Avatar
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    Re: 1992 4.9 Coolant Mystery

    Quote Originally Posted by BlackLac96 View Post
    Ranger,
    Yes it does. I'm pretty bummed because I was thinking that might be what it is and I've owned many of these engines, one with over 240K original miles and never had this problem. I guess I got a lemon.
    Don't just assume that. Give it the sniff test and get a block test kit and be sure.

    I don't recall if the 4.9 head gaskets can be done in the car (if necessary).

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    drewsdeville is offline Cadillac Owners Master
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    Re: 1992 4.9 Coolant Mystery

    Contrary to popular belief, the 4.X's have the same headbolt thread-pulling problem that the northstar does. In fact, you have to be wary of pretty much all aluminum blocked engines when replacing headgaskets, it isn't just a Cadillac thing.

    It IS possible to do the headgaskets with the engine in the car, if there aren't any damaged bolt holes. If they are damaged, you can't drill out the "bottom" side holes on either bank with the block in the car. There's just not enough room.

  8. #7
    BlackLac96's Avatar
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    Re: 1992 4.9 Coolant Mystery

    I've been a Cadillac fan ever since the 240K, it was a 1992 Deville I bought from the original owners, it had 145K on it when I bought it, was a Maryland car w/no rust on it. I was REALLY happy with this car but sold it due to finishing college and not having the $$ for a second car. From what I know the girl who bought it off of me drove it at least 4 more years, after that I lost track of it. But (back to this car) my "backyard" mecahanic is going to pressure test the 92 I currently own to check for the head gasket. What makes me think that they (the previous owners) were already aware of "some" issue is that there is a fitting to the right of the factory T-hose that looks like another T w/a cap on it that you can unscrew (about the diameter of your standard garden hose) Either this is for flushing the system or for air testing but it's not factory.

  9. #8
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: 1992 4.9 Coolant Mystery

    Yeah that T with the cap is for flushing. That's too bad about your engine. I could see a headgasket going bad if the water pump started leaking and the PO drove it while low on coolant and ignored the temp light because it's just a couple more miles to get home. Otherwise these engines are quite durable. Do the coolant test and you will know for sure.

  10. #9
    donwon is offline Cadillac Owners Enthusiast
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    Re: 1992 4.9 Coolant Mystery

    You metioned the "T" and restrictor. Do you know if the "T" actually has the restrictor and if the restrictor is in the right position?
    I had to get a "T" with no restrictor while one was ordered for me. No heat!

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