Draining radiator system

[thingsweregood]

I think I need to bleed my radiators and replace the coolant/antifreeze as I’m not sure how long it’s been since it was last done and I’m getting some overheating errors on my Autoterm diesel heater. 
 

Maybe a very basic question, but I’ve searched and every answer I’ve found says “drain the system and replace with a 50/50 mix of coolant and water”… but how do I best drain the system? Do I just drain it out the same place you bleed a radiator (seems slow and inefficient as the hole is tiny)? How do you then fill it up and ensure no air in the system? Do you fill it up whilst rad bleed points are open? 
 

apologies if I’m not using the correct terminology I’ve never done this before!

 

I have 3 radiators in sequence linked to a small header tank and an Autoterm heater in the engine bay. 

[MartinC]

Somewhere on the system you should have a drain cock

 

[Tony Brooks]

58 minutes ago, thingsweregood said:

I think I need to bleed my radiators and replace the coolant/antifreeze as I’m not sure how long it’s been since it was last done and I’m getting some overheating errors on my Autoterm diesel heater. 
 

Maybe a very basic question, but I’ve searched and every answer I’ve found says “drain the system and replace with a 50/50 mix of coolant and water”… but how do I best drain the system? Do I just drain it out the same place you bleed a radiator (seems slow and inefficient as the hole is tiny)? How do you then fill it up and ensure no air in the system? Do you fill it up whilst rad bleed points are open? 
 

apologies if I’m not using the correct terminology I’ve never done this before!

 

I have 3 radiators in sequence linked to a small header tank and an Autoterm heater in the engine bay. 

 

Once draind it may be a good ides to take the radiators out of the boat and give them a good flush through with a hose to clear and build-up of rust etc. I take it  that you do not have TVRs, if you do that might be causing the overheat problem.

[nicknorman]

Once you have found the drain cock, open all the radiator air bleeds whilst draining it, otherwise the water will be retained in the radiator. Then drain and flush it. To fill, you just add coolant via the header tank which should be the highest point on the system. Close the radiator bleed valves when coolant starts coming out. It’s much better if there are 2 of you, one to add coolant and one to check for coolant coming out of the air bleeds. After you’ve run the system you will probably need to bleed the radiators again, making sure there is always coolant in the header tank. With a cold system, you just want a bit of coolant in the header tank because it will expand when it gets hot and you don’t want it to overflow.

 

As to the mix ratio, I would use 30% or so of antifreeze. Too much concentration of antifreeze reduces the ability of the coolant to transport heat, and is unnecessarily expensive.

[David Mack]

1 hour ago, MartinC said:

Somewhere on the system you should have a drain cock

 

If you don't have a drain cock fitted then the way to drain down the system involves cracking a joint on a radiator connection (between the rad and the valve) and catching the water that comes out in a bowl or other receptacle that will fit. Tighten the joint finger tight while you empty the bowl into a bucket. Repeat ad nauseum. And have plenty of old towels to hand to collect the spillage. Once the pipework is drained and water stops coming out, open the bleed valve of the radiator you are working on and repeat the drain down sequence. Then open the bleed valve of the next radiator and so on. And before you start refilling the system, fit a drain cock to the lowest point to make it easier next time!

[Tracy D'arth]

1. Do not add neat antifreeze, premix it with water first as otherwise it will sink to the bottom and you will have trouble getting circulation.

[thingsweregood]

Thanks all for these very helpful tips.

 

I have yet to locate the drain cock (I have all plastic push-fit pipes, so maybe there isn't one), but it might just involve me removing the elbow joint sitting at the bottom of the engine bay below the header tank and trying to drain it there. Coincindentally, I have a small leak somewhere in the system because I keep needing to top up the header tank/bleed the rads a little bit and I'm 99% sure it's this elbow joint that's the culprit with a slow drip. So will try and replace that at the same time I drain the system. 

 

Tony Brooks - flushing the rads is a great idea, but might need to wait till spring when I paint the inside of the cabin because I'll need to remove them then. Too hard at the moment as a cc'er as not necessarily near a water point to do it!

 

 

[Tracy D'arth]

Small leaks for push fit fitting are often caused by tiny bits of cutting frizz in the seal because the pipe was cut with a hacksaw. Chances are that the fitting is OK.

You could replace the elbow with a tee and a drain cock whilst you are at it.

A wet vac is great for draining down when you have no drain, you can vac it up as fast as it runs out.

[thingsweregood]

3 minutes ago, Tracy D'arth said:

Small leaks for push fit fitting are often caused by tiny bits of cutting frizz in the seal because the pipe was cut with a hacksaw. Chances are that the fitting is OK.

You could replace the elbow with a tee and a drain cock whilst you are at it.

A wet vac is great for draining down when you have no drain, you can vac it up as fast as it runs out.

Would sanding down the pipe with some fine grain sandpaper work to smooth out any burrs? I assume that would prevent future leaks once seal/elbow is replaced.

[blackrose]

2 hours ago, Tony Brooks said:

 

Once draind it may be a good ides to take the radiators out of the boat and give them a good flush through with a hose to clear and build-up of rust etc. I take it  that you do not have TVRs, if you do that might be causing the overheat problem.

 

No offense intended to anyone, but if the OP is having to ask how to drain and bleed a C/H system, and if the coolant can be drained out of the radiator bleed valves 😊 then I very much doubt they'd be capable of taking the rads off and then reassembling the system satisfactorily.

[Tracy D'arth]

6 minutes ago, blackrose said:

 

No offense intended to anyone, but if the OP is having to ask how to drain and bleed a C/H system, and if the coolant can be drained out of the radiator bleed valves 😊 then I very much doubt they'd be capable of taking the rads off and then reassembling the system satisfactorily.

Have faith, we all had to learn somewhere.

[PaulJ]

20 minutes ago, blackrose said:

 

No offense intended to anyone, but if the OP is having to ask how to drain and bleed a C/H system, and if the coolant can be drained out of the radiator bleed valves 😊 then I very much doubt they'd be capable of taking the rads off and then reassembling the system satisfactorily.

I took Thingsweregood on the first ever time through locks (Lapworth in morning, Hatton in afternoon) All I can say is very capable and quick learner...😀

[Tony Brooks]

Some builders run the lower central heating pipe back into the aft bilge  and put tap or drain on the end.

[ditchcrawler]

4 hours ago, MartinC said:

Somewhere on the system you should have a drain cock

 

If you are lucky, some boats dont even have a drain down for the domestic water system