99 Burb Intake Manifold Gasket - JoeInSLO

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Posted by Guy ( on 13:55:06 09/11/07

In Reply to: Re: 99 Burb Intake Manifold Gasket posted by JoeInSLO

Hey Joe,
Thanks for your reply! I did take out the thermostat and the overheating is with no thermostat! Although I did not replace the fan, fan clutch, and fan housing during the chemical flushing/cleaning process that called for 6 hours of operation. I was being on the lazy side and felt that lite-duty operation would not require the R&Rx2 of the fan items. The fluid still looks both rusty and foamy and the system overheats to about 230 in about 20 minutes of idling. Is JoeInSLO in San Luis Obispo by chance? I'm in Morro Bay.

: Guy - your overheating is a classic case of a bad thermostat. If you want to verify it, take the thermostat out and run it without. You should have a very cold running engine. If it still overheats then you are in need of a new radiator core. That wouldn't surprise me with all the junk you said is flushing out. If you end up pulling the IM to fix the leaks be sure to lay a straight edge along the flange where it mates to the head to make sure it isn't warped. Have you tried re-torqueing the bolts where it is leaking? If you want to take the cheap route for a while try a tube of Bars Leak. That might dry out your weeping IM. If you do end up replacing the thermostat consider drilling a 1/8" hole in the thermostat's flange. Its an old timer's trick to simulate a 2 stage thermostat. I did it to my 90 and 91 3/4, 350 suburbans and they ran great. Very smooth and progressive water temp increase to operating temp. If you can find one, try the 180 deg thermostat. The original ones are 195 deg.
: Joe
: : I love my 99 3/4 ton Suburban 4x4 7.4L 454. I ve hade it since it rolled of the line, 130k miles ago. It started to get hot the other day, when inspected the radiator, wow what a mess! I have been flushing it for what seems like a week now. Removed the thermostat and disconnected the top heater hose and run water through it for over thirty minutes, still filthy. Added some heavy-duty chemical flush/cleaner, which required driving for 3 - 6 hours with the system sealed. The vehicle now overheats. I drove it for only 35 miles before the temp got to 240ish then stopped and had it towed home; now it over heats after about 20 minutes of idling. It appears to be seeping from the intake manifold gasket right behind the alternator and a little on the front of the driver's side also. I have tried to search the archives about this topic, with no luck. Any advice? Thanks in advance for any help!
: : Guy
: :

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