Exploding radiator bleed plug

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J

JoeClemson

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Bolton
I have a problem which I can't find anybody else having had. I have overheating problems with the vehicle and proably head gasket failings. Twice now, when the engine was overheating, the plastic radiator bleed plug has blown apart (presumably under massive pressure) and large amounts of coolant and steam have vented from the system. Both times this happened immediately the engine was switched off.

Some background. Some months ago I had coolant loss through the exhaust which I diagnosed as a head gasket problem. I treated the engine with Steel Weld and the problem went away. Recently I noticed coolant dripping under the engine and saw it was coming from around the expansion cap. The engine was also beginning to overheat. I replaced the cap (twice) but the overheating continues, though with minimal coolant loss. Overheating only seems to occur after a few miles of fast running. On both occasions I've been out on a fast run (20 miles or so, 5 on the motorway) the engine starts to overheat (I've not let it get as far as the red zone) and then when I stop the engine - steam and coolant explode from the bleed screw.

Having fitted a new radiator bleed plug I now notice that the coolant is again appearing at the exhast pipe, along with light white smoke.

The vehicle is fitted with an old LPG conversion so the coolant is also routed through the vapouriser, but that appears to be operating normally.

I'm pretty certain one or both head gaskets need doing, but I want to be reasonably sure that doing them will fix the issue and I can't get my head round what would cause the radiator bleed plug to explode with this precise timing, and this part rather than any other part of the coolant system.

The viscous unit, thermostat and drive belt have all been replaced.

Any Disco gurus out there with an insight on this?
 
I am surprised you still have those plastic bleed plugs - I thought everyone changed em for radiator valves as a first lo-cost mod?

You used Steel Weld? I reckon its blocked some of your coolant passages - strip the heads orf and clean out the water system thoroughly and rebuild, replacing anything that looks dodgy.
 
The Mad Hat Man said:
I am surprised you still have those plastic bleed plugs - I thought everyone changed em for radiator valves as a first lo-cost mod?

You used Steel Weld? I reckon its blocked some of your coolant passages - strip the heads orf and clean out the water system thoroughly and rebuild, replacing anything that looks dodgy.
Click to expand...

Being an ordinary motorist with a slight mechanical bent, I've never heard of radiator valves. Where can I find more info?

If the water passages are blocked up is cleaning them going to be feasible? I don't know much about them but I imagined they would be narrow, bendy and generally inaccessible - particularly in the engine block. Would pushing some wire through them work?

Forgivem me if the questions seem basic and stupid but I'm beyond my comfort zone here.
 
I am sure you have heard of a Domestic Radiator Bleed valve ;).
bleedvalve.jpg


You could try reverse flushing the engine and cooling system with a hosepipe - that might clear out lots of crud, before you strip the heads off, but if you have water in the exhaust - unless its condensation, you will need to take the heads off to check.
 
JoeClemson said:
Being an ordinary motorist with a slight mechanical bent, I've never heard of radiator valves. Where can I find more info?

Forgivem me if the questions seem basic and stupid but I'm beyond my comfort zone here.
Click to expand...

The V8 disco has coolent filliing plug on top of the radiator, diesel engines also have a plug in the thermostat housing.

If there is an air lock anywhere within the cooling system, (although V8's don't seem to suffer like the diesel with this problem) part of the method of removing the air it is is to remove the plug/s and "bleed" the air out of the system and then topup with coolent.
 
discool said:
Over pressure I would have thought would have been taken care of by the valve in the expansion bottle cap, so it's possible the threads on the plactic rad cap were a bit iffy.

:welcome2: to the FORUM JoeClemson
Click to expand...

This is what really mystifies me. I've tried two new expansion caps and I'm on to my third radiator bleed plug. It's possible the first bleed plug was old, overtightened and weak. The second was brand new. In both cases the pressure blew the top off the bleed plug, leaving the threaded part stuck in the hole.

If the problem was excess pressure in the cooling system as a whole I would expect a pipe to burst or the expansion cap seal to give way. Add to this the fact that on both occasions it happened precisely at the moment I switched off the overheating engine.
 
discool said:
The V8 disco has coolent filliing plug on top of the radiator, diesel engines also have a plug in the thermostat housing.

If there is an air lock anywhere within the cooling system, (although V8's don't seem to suffer like the diesel with this problem) part of the method of removing the air it is is to remove the plug/s and "bleed" the air out of the system and then topup with coolent.
Click to expand...

I've been careful to bleed the air out of the system at the radiator bleed plug when topping up and when refilling after the explosions I've described.
 
#You unscrew that crappy plastic plug and replace it with the domestic rad valve - if yu have a key then yu can crack em open whilst hot - to let any air escape too;).

9747d1239640618-exploding-radiator-bleed-plug-p4110036.jpg
 

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good question - dont know - but it fits.:D if in any doubt - take yo old placky one with ya. But be careful - they are prone to breaking.

They do come in different sizes, for example 1/4", 3/8" or 1/2" B.S.P etc. - here is one at B&Q.
 
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