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99 4.0 sudden overheat


 
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Yukonhigh
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Joined: 07 Mar 2009
Location: Cape Cod

PostPosted: Sat Mar 07, 2009 4:44 pm    Post subject: 99 4.0 sudden overheat Reply with quote

Just wondering if anyone has encountered a similar issue. I have a 99 GC 4.0 and recently drove it from Mass to Fla. On the ride home it overheated almost instantly. The temp outside was in the 30's, truck was running fine but the heat went cold like someone flipped a switch,looked down and the temp gauge was pegged and it was overheating. Figured maybe the thermostat had broken, had it replaced the next morning, same thing,overheats after just a few minutes,no circulation, pushes cold water slowly into the overflow tank, bottom hose and one htr hose cold. Ran it with no thermostat, same deal. The waterpump is new ( 3 months ), new temp sensor in back of headlight, fan is working fine, no milk in the oil, runs fine no skip, doesn't seem to be pushing water out the exhaust, bottom hose isn't collapsing.
I know the 4.0 is prone to overheating when the coolant hasn't been bled correctly after a radiator, waterpump change etc. I'm just at a total loss why this happened with no gradual symptoms and came on so suddenly. Any thoughts on this would be greatly appreciated. Thanks, Dana
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DCJEEPGC
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Joined: 16 Sep 2008

PostPosted: Fri Apr 03, 2009 9:45 am    Post subject: Reply with quote

Was wondering if you discovered the problem yet. Sounds like a circulation problem. Engine shouldn't overheat at highway speeds unless it is either down in coalant or the coolant isn't circulating through the rad. Flushing the rad, if you haven't already done so, or rechecking that lower rad hose might be a place to start. Some guys have used that rad stop lead crap and find that it can eventually clog up the system somewhere down the line.
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XJwheelerZJ
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Joined: 11 Apr 2009
Location: tahoe

PostPosted: Sat Apr 11, 2009 12:54 pm    Post subject: Reply with quote

sounds like you have an air bubble somewhere you can pull a hose and fill there i also recomend hood scoop or louvres if you're rock crawling
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Greg G
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Joined: 30 Jan 2009
Location: Johnson City, TN

PostPosted: Tue Apr 14, 2009 7:15 am    Post subject: Reply with quote

I agree - My sons did the same thing because he did not let the system settle out after installing a thermostat in his 92. I let the engine run for a little while and cracked the radiator cap over night. Knock on wood it has not happened again.
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Greg G
http://powerandplay.com

1997 ZJ Grand Cherokee - 3" lift - BFG's
1992 XJ Cherokee - 4" lift - BFG's
1980 CJ-7 - 1 Ton way to much to list
1983 SJ Grand Cherokee
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