Replacing coolant with heater above engine?

[N Coast Murray]

Our Yanmar 4JH2-UTE has a Red Dot heater about 2 feet higher and 3 feet away from the engine.

What's the trick for getting coolant up to the heater when replacing coolant in the engine?

Scoured that inter-webby thing, but found diddly-squat.

[rslifkin]

It'll depend a bit on the engine and how well it all self bleed.

Personally, I'd fill the system and start the engine with the cap off the heat exchanger. Top it off until the level stops dropping. Then throttle the engine up to 1500 rpm or so and top off again. Once the level stops dropping, install the cap and see if the heater is getting warm and whether it sounds like there's an air/water mix gurgling through it or not.

If you're lucky the engine will be able to push the air through and out without much trouble. If not, once The system warms up a little more and builds a little pressure, shut the engine down and crack a connection at the heater (be careful and shield yourself against any spray) until it stops spitting air and gives just coolant.

Once it's bled, monitor the coolant level in the overflow tank over the next few heat cycles. The level may drop a bit as any last bits of air work their way out.

[Stu Jackson]

Originally Posted by N Coast Murray

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What's the trick for getting coolant up to the heater when replacing coolant in the engine?

The "trick" is as it has always been: get the air out of the system.


You have to think of this backwards FROM your "...getting coolant up to the heater..." TO filling up the hoses between them.


Fill from the top and get the air out of both hoses.

[N Coast Murray]

Thanks for the replies.

Guess I didn't run the engine long enough or at high enough rpm for the level to keep dropping. Will take another stab at it tomorrow.

My plan was to 'fill from the top' at the heater, but...the previous owner of the boat must have had forearms as big as my thighs. Everything with a nut or clamp on it is tight, tight, tight! The hose clamps on the heater had buried themselves into the hoses so far that when I tried to loosen the clamp, the screw mechanism came out and the clamp stayed put.

If it's not blowing 30 knots tomorrow like it was today I'll go for a slow spin to put a load on the engine and watch for the coolant level to drop, then keep an eye on the overflow tank until things balance out.

[rslifkin]

There is a chance the heater is just too high up and the water pump on the engine isn't powerful enough to push the air out of it. If that's the case, you can either bleed the air out of the output side of the heater, or just fill from the top (with the pressure cap on the heat exchanger installed). If you fill from the top, you'll likely still have a little air somewhere that'll work its way out after a couple of heat cycles, so definitely watch the expansion tank level.


Assuming the heater is plumbed to bypass the thermostat (like the heater loop in a car), engine temperature, load, etc. shouldn't matter for bleeding. It's just a matter of bringing the RPM up enough to get more water pump output pressure and hopefully reach a point where it can force the air out of the heater.

[FPNC]

You have to install a 'header tank' with a pressurized venting cap at a point that will be the highest in the system. Use that tank to fill the system and it will provide pressurized ventilation for the system. Install a higher pressure cap on the engine so it will not vent. You want all venting to take place at the highest point in the system. Which is the header tank.

[N Coast Murray]

Bit of an update.

Shut off hoses to heater at engine, cut the super-duper tight hose clamps off at the heater, filled hoses and heater with coolant (there was already coolant in there, so just topped it up) and reattached hoses to heater.

We are into day three of 25 to 35 Knot northerly outflow winds, so can't really go for a romp to get the engine hot enough for the thermostat to open. Tried running engine in slip, but the north coast BC waters wouldn't let the engine get past about 70 Celsius, which is frustrating because the thermostat opens at 75 to 78 Celsius.

Maybe tomorrow...