Bleed Coolant System (?)

[JonnyT]

Hey Yall,
I have just passed the first start on my Mk II Roadster build, and I am trying to bleed the coolant. However, I am having an issue i am unfamiliar with.. I topped off the radiator, put in my fill funnel, and start the roadster. The coolant level stays pretty even until the temp gauge hits 200, and then the funnel starts filling and filling until it overflows while the temp continues to climb. My first thought was a faulty thermostat, but i've replaced it with a new thermo and the issue persists. Could it be an issue with the water pump? Something else i havent thought of? Any tip or advice would be helpful.

See photos of the setup below.187187187188

[Its Bruce]

I can't tell how your coolant is routed and elevated in the photos, but it sounds like it's doing what you'd expect. The thermostat is opening and allowing coolant to flow through fill device. The path of least resistance is out your funnel.

Is there something that makes you think there's air in the system? Is the fill point at the highest elevation?

[MB750]

Where's the coolant fill? I can't make heads or tails with what you got going on at the front of your engine.

[rich grsc]

Thats a very weird cooling set up. I see the coolant bypass at the thermostat housing is blocked off, which means no coolant moving through the block till the thermostat opens? You don't have a fill point at the highest location in the system that I can see? Your over flow tank isn't going to work laying on it's side, and I don't think you can move enough water through those two small hoses to keep the engine cool.

[steno]

Perhaps your desire to build a better mousetrap has come to haunt you. There seem to be many places to hold air and restrict water flow.

[MB750]

Perhaps your desire to build a better mousetrap has come to haunt you. There seem to be many places to hold air and restrict water flow.

Is that what's going on here?

So, apparently 100 years of automotive cooling system design isn't refined enough for him.

[Mastertech5]

Is that your coolant fill on the upper hose just behind the fan shroud? If so, move it to the thermostat housing end.

[JonnyT]

Thank you all for your suggestions! For context - i inherited this build from a family member and I'm trying to finish the build. This cooling setup was already assembled and i'm just tying to get it to work :) Luckily i was able to trouble shoot, the water pump had a lousy ground and wasn't running consistently, causing the radiator to overfill when the thermostat opened up. With the water pump running as it should, the issue has resolved.

[Its Bruce]

I'm glad the issue is resolved, but being very candid, I still don't even understand your explanation of what happened. Come on back if the issues reappears.

[Norm B]

For some reason the original builder spent a lot of time, effort and money to remove the belt driven water pump. As Rich pointed out there is no coolant bypass and I don’t see a way to set one up with easily with your current setup. The coolant bypass is very important during initial engine warm up after start. Without it you could get very hot spots in the engine, especially in the heads around the exhaust ports, that could result in warped or cracked heads and blown head gaskets.
The other thing I noticed is the flow divider you have installed, to feed coolant to the left and right banks of the engine, looks like it is supposed to be fed from both ends. With the way it is hooked up now, it is very unlikely that both sides will receive equal coolant flow.
Will be interesting to see how this works out.

[MB750]

This is full of cringe. Saying something can cause the "radiator to overfill" implies it's supposed to only be partially filled by design. That's a great way to cut down heat transfer from the engine. I'd really like a closer look on this system.

I'm also wondering what's so bad about the OEM system that someone thought this mess would be a good idea?

[Mastertech5]

Maybe you should just start from scratch.