How to remove block plug on '91?
Thread Starter
Burning Brakes
Joined: Feb 2008
Posts: 988
Likes: 7
From: Sarasota Fl
How to remove block plug on '91?
I've got a '91 L98 auto. I'm currently replacing the intake manifold gaskets on it and have drained the coolant from the radiator using the petcock. Turns out that when I got my coolant hoses changed more than a year ago, they put dex-cool in it! 
So I want to thoroughly clean everything out - block, radiator, overfill tank, surge tank, hoses and refill with distilled water and the true green coolant. I am changing the water-pump at the same time and the thermostat (and gasket) for a 195* AC Delco.
I searched the archives and found posts about the '92 and up cars and cars older than the '91 that have a six-sided block plug on the driver's side. I know how to remove the knock sensor on the passenger side with a socket after removing the shield and wire, but I'm not sure about the block plug.
After 2 or so months, I finished my transmission rebuild and now have this coolant problem. Help me get it back on the road ASAP.
Thanks in advance,
Jonathan
So I want to thoroughly clean everything out - block, radiator, overfill tank, surge tank, hoses and refill with distilled water and the true green coolant. I am changing the water-pump at the same time and the thermostat (and gasket) for a 195* AC Delco.
I searched the archives and found posts about the '92 and up cars and cars older than the '91 that have a six-sided block plug on the driver's side. I know how to remove the knock sensor on the passenger side with a socket after removing the shield and wire, but I'm not sure about the block plug.
- Is it threaded or does it just pop out? I was going to try a pair of heavy duty retaining ring pliers that I have and try and twist it out.
- Is there a special tool for removing this driver's side plug?
- Should I put teflon tape on both the block plug (if its threaded) and the knock sensor when I replace? I remember reading something about the use of teflon tape, but don't remember if it said to use it or stay away from it.
- Any tips on how to keep all the wires around the knock sensor and block plug dry?
After 2 or so months, I finished my transmission rebuild and now have this coolant problem. Help me get it back on the road ASAP.
Thanks in advance,
Jonathan
Last edited by janarvae; Aug 23, 2008 at 12:20 AM.
Drifting
Joined: Dec 2005
Posts: 1,313
Likes: 2
From: High Ridge Missouri
As you already know pass side is the knock sensor, but there is no plug on the drivers side. To drain the drivers side remove the hose coming from the oil cooler (or as some call it the oil heater) to block (the drain was replaced with a coolant nipple that is connected to the oil cooler circuit).
Hope this helps.
Hope this helps.
Thread Starter
Burning Brakes
Joined: Feb 2008
Posts: 988
Likes: 7
From: Sarasota Fl
So what is that rounded plug looking thing in the picture (I see it on the other side of the block too)? I've since replaced all the plastic conduit that deformed in this photo, FYI....
And so that six-sided head is the plug? And the FSM says no thread sealer when reinstalling - is this true if its the old knock sensor?
Edit: I saw the FSM photo of the oil cooler, and it looks like I don't have one.
Thank for the quick responses,
Jonathan
And so that six-sided head is the plug? And the FSM says no thread sealer when reinstalling - is this true if its the old knock sensor?
Edit: I saw the FSM photo of the oil cooler, and it looks like I don't have one.
Thank for the quick responses,
Jonathan
Last edited by janarvae; Aug 23, 2008 at 09:11 AM.
Melting Slicks
Joined: May 2001
Posts: 3,014
Likes: 18
From: Raleigh, NC
If you pull out the knock sensor, most of the coolant will come out. Once the knock sensor is out, just add water through the thermostat hole until the water runs clear out the knock sensor hole. The coolant passages in the block are all connected, running water through is this manner should remove nearly all the Dex.
Thread Starter
Burning Brakes
Joined: Feb 2008
Posts: 988
Likes: 7
From: Sarasota Fl
If you pull out the knock sensor, most of the coolant will come out. Once the knock sensor is out, just add water through the thermostat hole until the water runs clear out the knock sensor hole. The coolant passages in the block are all connected, running water through is this manner should remove nearly all the Dex.
Thanks,
Jonathan
Melting Slicks
Joined: Feb 2006
Posts: 2,753
Likes: 15
From: backwoods upstate ny
use an 18" breaker bar and a SIX POINT socket on the drivers side plug...pre-soak overnight with kroil before attempting removal may help...i have seen only ONE plug twist off in over 50 years on SBC-1's, seen dozens with plug corners rounded off by 12 point socket...heat the plug to cherry red and allow to cool once, then heat to cherry red again and touch a birthday candle to the juncture of plug/block to "wax the threads" for really ez removal (ol fart's trick, don't laugh - it works)
Thread Starter
Burning Brakes
Joined: Feb 2008
Posts: 988
Likes: 7
From: Sarasota Fl
use an 18" breaker bar and a SIX POINT socket on the drivers side plug...pre-soak overnight with kroil before attempting removal may help...i have seen only ONE plug twist off in over 50 years on SBC-1's, seen dozens with plug corners rounded off by 12 point socket...heat the plug to cherry red and allow to cool once, then heat to cherry red again and touch a birthday candle to the juncture of plug/block to "wax the threads" for really ez removal (ol fart's trick, don't laugh - it works)
Just went and checked that my 14mm fit perfectly over the driver's side plug...And no teflon tape when replacing? Thanks,
Jonathan
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Melting Slicks
Joined: Feb 2006
Posts: 2,753
Likes: 15
From: backwoods upstate ny
the ONLY place for teflon tape use is large threaded cold water piping where pipe may not be perfectly round and getting leak-tite seal in the threaded fittings is problematic and a minute leak is only an inconvenience (natural gas piping is definitely not in this category), NO place on your vette unless temp emergency dictates..."paste" type thread sealer should be used where-ever "pipe" threads are made up (your block drains are 1/4" npt)...paste type of "pipe dope" with teflon added in formulation is best for nearly all applics but care should be taken that the lubricity of the teflon does not make the fitting/plug turn so ez that the connection is "cranked in" excessively tight, possible SPLITTING the outer housing (i have seen this done by a "98 pounder").
i always use teflon paste on block drain plugs/knock sensors, others have their opinions, you decide
btw, block drain plugs on L98's were "originally" 9/16" hex head...if corrosion has reduced head size (not uncommon) so that a smaller six-point socket will fit or can even be "driven on" with minor hammer work, do it 2 it.
i always use teflon paste on block drain plugs/knock sensors, others have their opinions, you decide
btw, block drain plugs on L98's were "originally" 9/16" hex head...if corrosion has reduced head size (not uncommon) so that a smaller six-point socket will fit or can even be "driven on" with minor hammer work, do it 2 it.
Last edited by redrose; Aug 23, 2008 at 01:54 PM.
