Rather then epoxying the end of the T shut, I'd recommend a small length of hose with a metal plug and 2 hose clamps. With all the thermal cycling the thing will see, I wouldn't trust a blob of epoxy not to blow out at the worst possible time.

Good advice mrmad. I should do that.

My advice to get it working.

(1) Be careful, if it boils or you get an air-lock, then it might burn out.
(2) You must have the heater control on *full heat* or it blocks off the flow :) This is what happened to mine, luckily a fuse went rather than the
whole thing.
(3) Consider getting a small pump. A 12v one would do, together with a low-power 12v transformer. Get an impeller type pump that doesn't impede normal water flow. Use this to circulate the water around the engine for a much better coolant heating effect.

Without (3) above, it will not be very good at all, as, the water flow to/from the heater matrix is horizontal so convection will not work very well.

Finally, even my 3kw engine heater (currently needing to be serviced so my MPG is dropping) doesn't get my engine up to temp, but about half-way (which is well over the amount to avoid enrichment, and makes the engine run very smooth from the start).

Edit - maybe the reason for the temperature readings are as follows:

(1) It heats up due to convection
(2) It only heats up a bit more, as convection is inefficient
(3) Thermal cutout as the heater temperature gets too hot

It's got a thermostat... but I wonder if it would work if there's air in the tank - it might not transmit heat to the t-stat.

check!

The instructions were to place the tank several inches below the water pump return line, which I did. Also it's got check valves, so theoretically, once coolant starts moving "up-hill", it should draw flow from the heater core and start a loop going.

Anyway, I'll get a chance to have a second look at it this weekend.

I agree a pump would be best. Yet another reason to convert my water pump to electric (rather than adding an additional one).

Thanks for the tips.

would get more complicated but how about a one way clutch under drive pulley and an electic motor so that the electric motor could drive it when you want more capacity flow or engine off flow and the clutch pulley would drive it the rest of the time more slowly under light load. This way you will not have to worry about wearing out the electic motor - unless you are going brushless. You could also run a fan blade on the water pump to turn it by the wind flowing through the radiator at high speeds but I think it will require faster spinning than that.

The car is already close to being overly complicated from my mods! I certainly couldn't let anyone else drive it the way it is. I'd have to give them warnings & instructions about all the things I've disabled/modded - what switches work, what gauges to watch closely, etc.

Holy hot sauce Batman! 3kw coolant heater. How the heck do you plug it in, 240vac?

Anyway I have noticed mine not warming up as much as it used to. I believe though what is really happening is the thermostat opens sooner and starts to heat up the radiator, it never used to do that, maybe I blew the thermostat out? On the plus side it actually warms more coolant. It used to be I would start after 2 hours (1000 watt) and I would see coolant at 200F, then it would drop to 140F or so after a minute then slow climb again. Now it starts at 160 or so and stays there never dropping.