A couple of, embarrassingly elementary, questions about heat exchangers.

[NealB]

Our lovely old Seamaster 34 has twin Thorneycroft/ BMC Commander diesels. Both engines are in very fine fettle, and were fitted with new Bowman heat exchangers about 5 years ago (which have '250' cast into the body).

I feel rather nervous at revealing the profound depths of my ignorance to such an august audience, but here goes:

1) opening the drain tap in an engine block will drain the anti-freeze from the 'closed' side of the system, but will leave a little in the rear part of the heat exchanger (as the engines are installed with a slope, downwards towards the stern, of around 10 degrees). Therefore, to drain a heat exchanger completely, I'll also need to remove the plug situated near the exhaust manifold. Is that correct, please?

2) due to the aforementioned slope, no coolant is visible when the car radiator-type cap is removed. I'm therefore a bit nervous of refilling the heat exchanger: could adding too much coolant cause any damage to anything?

Thank you for your thoughts.

 

[jwfrary]

As to removing coolant I wouldn't worry unless your changing coolant types. If you want to be super keen then flush it with fresh water first.

Level wise the overfilling will simply result in a bilge full of coolant no damage will be done

 

[pvb]

Similarly, I wouldn't worry too much about draining the antifreeze completely. You won't damage anything by adding too much coolant.

 

[oldgit]

On the header/expansion tank on my Volvos when the engine cold can just about detect the water at bottom of tank with finger .

 

[NealB]

The reason for my caution with topping up the coolant, is that I have very vague memories of reading a warning, long, long, ago, that overfilling could possibly lead to coolant getting into the cylinders.

I didn't really understand how that could happen ...... something to do with the exhaust manifold, maybe?

Or could it be a false memory?

 

[duncan99210]

I’d say that the tale about coolant in the cylinders is a false memory. Fill the coolant side of the heat exchanger following the quantities given in the engine manuals: any excess will be vented through the filler cap.
That said, you can get raw water in the cylinders if you don’t have a functioning siphoned break in the system or if you turn the engines over for too long trying to start them.

 

[VicS]

The reason for my caution with topping up the coolant, is that I have very vague memories of reading a warning, long, long, ago, that overfilling could possibly lead to coolant getting into the cylinders.

I didn't really understand how that could happen ...... something to do with the exhaust manifold, maybe?

Or could it be a false memory?

Nor do I, but only fill it to an inch or so below the filler neck
Any excess will be expelled via the car type pressure cap. Direct the overflow to a suitable vessel to avoid it going into the bilges