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Changing antifreeze - engine overheating


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Its unlikely but I have heard of car coolant pumps with plastic impellers that fall off but not yet on a boat engine. I think I may be tempted to take that elbow pipe off the header tank and turn it so the header tank end points upwards. Plug the hole in the header tank and fill coolant and then start and rev the engine. If the hose fills up and overflows, probably slowly because of the closed thermostat, then you know the water pump is working.

 

When you took the thermostat out did you notice if it had a small hole in the flange, maybe with a jiggle pin in it.  If not I would be very tempted to drill one before refitting it. Say about 4mm or so. That way you will get some coolant flow that might help displace any air and should also allow air to work its way into the header tank when the thermostat is closed.

 

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43 minutes ago, Tony Brooks said:

Its unlikely but I have heard of car coolant pumps with plastic impellers that fall off but not yet on a boat engine. I think I may be tempted to take that elbow pipe off the header tank and turn it so the header tank end points upwards. Plug the hole in the header tank and fill coolant and then start and rev the engine. If the hose fills up and overflows, probably slowly because of the closed thermostat, then you know the water pump is working.

 

When you took the thermostat out did you notice if it had a small hole in the flange, maybe with a jiggle pin in it.  If not I would be very tempted to drill one before refitting it. Say about 4mm or so. That way you will get some coolant flow that might help displace any air and should also allow air to work its way into the header tank when the thermostat is closed.

 

I think I already made the mod to the stat several years ago if my memory serves me correctly? Anyway I'll have a go with these suggestions tomorrow once I get some more antifreeze and report back.

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1 hour ago, john6767 said:

As you have already opened up the thermostat housing, would it be worthwhile leaving the thermostat out temporarily so that you get good water flow through the skin tanks at lower temp.

It's back in and the housing is reassembled now but it's easy enough to take it out again

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Update: I got some more antifreeze this morning. Put about 3 litres more in and filled the coolant reservoir almost to the top, squeezed a few hoses but didn't notice any air coming out, put the pressure cap back on and ran the engine for about 20 mins in gear to get the temp up. 

 

It sat on about 80C and didn't go any higher so all is well. Although I'd already put 40 litres of antifreeze in before I guess it hadn't got to the level of the pump, even though I could see coolant at the bottom of the reservoir. I've never had to fill the reservoir all the way to the top before, but anyway it's working fine now. The pipes to/from the calorifier are hot and the first skin tank is getting warm. The second skin tank is still cold. It takes a good long run to warm that one up.

 

Thanks everyone for the help

Edited by blackrose
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2 hours ago, blackrose said:

Yes, a tad embarrassing, but after putting 40 litres in and seeing coolant in the tank I thought it was full. Hope the water pump has suffered no damage.

Exceptionally unlikely to have even noticed. The only parts that make contact MIGHT be a lip seal or a carbon face seal. Neither of which demand water to lubricate. Usually the clearance between impeller and housing is measured in excess of 5mm, its when they touch you get problems. (Bearing failed and seal leaking.

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13 minutes ago, Cheshire cat said:

Glad you are OK again. You need to set the level correctly now so that the expansion tank doesnt overflow.

I tend to fill close to the top and the excess (as it warms up) gets expelled down a bit of pipe pushed on to the overflow spigot by the rad cap in to an old 5 litre coolant container.  This can then be used from topping up if ever required.

 

As an aside I used to loose a bit of coolant, could never work out where from so I put some (about half a teaspoon) Drain Tracing Dye Fluorescein into the coolant when I mixed it with DI water and poured it all in.  After a couple of short trips a bit had leaked out and using my uv torch (few quid from ebay) in the dark (it needs to be pretty dark as it is a dim glow) I found the source of the leak.

Edited by Chewbacka
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6 hours ago, Mike Tee said:

I know I'm working with hindsight here, but did you measure how much you took out?

No I didn't. I'm not sure how that would have been possible as it was all over the engine room floor. It's pretty difficult to collect what comes out of the engine. I suppose I could have measured what I managed to wetvac up, but to be honest it was all a bit of a mess at the time and I wouldn't have been able to measure it to the litre because some of it was soaked up with old towels. I was only 3 litres out with what I put back in. Anyway, now I know it's exactly 43 litres.

5 hours ago, Cheshire cat said:

Glad you are OK again. You need to set the level correctly now so that the expansion tank doesnt overflow.

 

Thanks. I have an overflow header tank connected to accommodate any expanding antifreeze that spills out.

Edited by blackrose
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6 hours ago, Tony Brooks said:

Exceptionally unlikely to have even noticed. The only parts that make contact MIGHT be a lip seal or a carbon face seal. Neither of which demand water to lubricate. Usually the clearance between impeller and housing is measured in excess of 5mm, its when they touch you get problems. (Bearing failed and seal leaking.

Ok thanks, that's good to know.

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