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E34 (1989 - 1995)

 
 
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Old 10-31-2012, 09:34 PM
robertobaggio20 robertobaggio20 is offline
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Join Date: Oct 2009
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Useful fix if you have bleed screw problems

Hi Everyone,

I recently had a problem with my old radiator. The bleed screw would not screw itself in nicely. It kept turning and turning and would not tighten and stop. Now please bear in mind that the bleed screw can be tightened ad infinitum with increasing force, but that should not be done at all. As long as it reaches a point where it feels normally tight, you can stop there. That's usually where I stopped, but this time it kept turning and turning.

Upon close inspection, it became clear that the thread in the bleed socket had faded out. There were no cracks.

This is how I solved the problem :

1. I wound pvc tape ('pipe tape ') around the bleed screw several times and screwed it in.

2. It still kept turning and turning without tightening.

3. I then wound even more pvc tape. This time, it was too much and I could not screw it in properly.

4. So, I used an intermediate length of tape intermediate between the two steps earlier. It still kept on turning in the socket, but I decided to leave it. Ran the engine at idle for 15 minutes. No problems, no leaks, escaping coolant, or steam (you must check for steam). Drove the car off. 25 minutes later, reached home and double checked. No leaks or steam.

5. Subseqently, I removed the old pvc tape, used some new one, and then applied a large dollop of white high temp silicone window sealant. Then I screwed this in. Again, unfortunately, the bleed screw kept turning and turning, but I stopped it as I pressed it down and it seem to reach near the correct height it should be.

6. A large amount of the sealant had splayed out of the socket during the tightening process. This is normal.

7. Left it for 30 minutes to set. Then drove off. Checked for steam at the socket on several occasions after that. No problems. Drove the car damn hard as well, and checked. No problems.

While using both of the methods above, the engine's temperature was perfectly normal.

The more permanent fix for this problem is to use a rethreading die to cut a fresh thread into the bleed socket, then wind the white pipe tap around the bleed screw, and then finally screw it in decently. This will avoid the need to repeat the sealant procedure each time you remove the bleed screw to bleed the radiator.

These procedures were actually more successful than I expected, considering that in both occasions, the bleed screw could be kept turning on and on. Was quite concerned that it wouldn't last under pressure. No problems whatsoever. God did not have to be great this time, the sealant and pipe tape sufficed.



rgds,
Roberto

p.s. White pipe tape can be wound around to form an O ring effectively for anything. I wound a little bit extra near the top of the bleed screw where the existing O ring was, before winding it around the thread itself, in both of the procedures listed above.
p.p.s. If you ever need to do this, let the engine reach operating temperature and check to see that there are no leaks and no steam (hold your hands or a place a cup over the bleed screw, or shine an led flashlight close to the area) before you drive off. Check this every day for 3-4 days right after you've finished driving for the day, while keeping the engine running at idle. If there are no problems and no hints of a problem, then its a solid fix.
p.p.p.s. Retreading is the only long term fuss free solution.
p.p.p.p.s. Changing the radiator is the only worry-free solution. You may ultimately elect to do this - radiators are fairly cheap these days and if you know how to remove your clutch fan, its not hard to change the radiator at all and kinda fun (remember to tie up the transmission cooling lines to prevent excess oil spillage, and remember to use carb cleaner and simple green to clean the ac condensor that becomes exposed when the old radiator is removed). However, with this fix, you do not need to have your show stopped right on the spot, and you'll have time to decide your schedules and workshops etc. If you don't change the radiator, no problem. Whenever you bleed the radiator (flush the coolant once a year) then you'll just have to reapply the high temp clear/white silicone window sealant again. Removing the bleed screw ruptures the old sealant.
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