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Set up is as attached. Fiat thermostat, which like some late model Fords, relies on "dead heading" of the radiator core to stop flow.
All season street use in Canada (so not just including heater, *especially* heater, ha!)

Pair of blue-ish upward arrows at front of motor are meant to mean inside the block, pressured by the pump.

Small red "hook" at back is flow from head to heater core.
Long slim perfectly straight orange line would be heater core outflow. Not sure- assuming you guys see everything else as workable- where the best point of return back into the system, should be.

Should work? Y/N?

Whats the best way to hook up a heater core circuit?

My only concern is, you need something in there to eliminate the flow from the head back into the WP when the radiator is open. ..
Otherwise the water will take the path of least resistance and bypass the radiator, going back into the suction side of the pump.
IIRC Ford uses a spring loaded valve on the head to WP hose. Lotta brain fade lately. ..........

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"There are times when a broken tool is better than a sound one, or a twisted personality more useful than a whole one.
For instance, a whole beer bottle isn't half the weapon that half a beer bottle is ..." Randall Garrett

Some fiats have the heater hose connection directly on the stat housing.

Well, thank you MiataV8... You put a lot of effort into that.
Was the entire revision of the pic due to my set up having a "fatal flaw"? or maybe starting fresh helped you sort it out?

I have to admit a couple minutes looking haven't turned up the critical difference, between my illustration and yours.

Actually, a detail (?) to confirm: in my mind, the rear light blue arrow I would have expressed as reversed- as an output to the heater core. Agree?
My concern for a return is: the upper "option" at the front in your light blue "two options" is under (dynamic, pumping) pressure. aka Highside. Therefore, flow in the heater core would stagnate. Now the lower option is, I think close to what I was thinking.
Let me run this by you, as it has one critical difference from yours, which is: it's to the right of the thermostat in the pic.
My thought- see where the black water pump inlet is? Three fairly widely spaced bolts, looks like a thermostat housing. In fact, in your version, you left a small square of my light purpley blue (lavender?). What if I was able to make- right exactly there at that accidental mark- enough of a boss for an appropriately sized ORB fitting, and return post heater core coolant right there. Ideal, no?


What about the above posters concern for "short circuiting"?

The light blue arrows are tap points, not flow direction but I did make a mistake. The way I drew it, the heater would shut off once the thermstat opened, blocking the flow from the head to the waterpump inlet.
The tap points at near the stat must be able to bypass the stat when the stat is in either position.

A heater flow is parallel and essentially a "short circuit", so we restrict the flow to force most of it through the block and head. The greater the restriction, the more flow will circulate through the block and head when cold and the radiator when hot. Warm up will also be faster. I use a nut in the hose or a washer over the end of the fitting inside the hose.

Why not use the thermostat housing designed for this engine.
What is this 4 cylinder pushrod motor from, anyway?

Mercruiser marine inboard. This is the 3.7L based around the Ford 460 head, pistons & connecting rods. Or in this case, Diamond racing pistons, Manley connecting rods for the offset ground crank, and a Kaase Boss429 semi-hemi repro head. 253 Cid.

So, no heater core OE.

The OE intake had a thermosat housing, but that intake wasn't one I wanted to use, The original picture shows me laying out a showy long tube intake runner set, with Chrysler Intrepid 3.5L throttle bodies for each cylinder.
Anyway, the OE coolant flow was... complex. I have technical drawings on another computer- they will raise eyebrows. It makes the Audi Biturbo cooling system, regarded as the most technical of automotive systems, look simple. In this case it involved cooling the exhaust manifold, heating the intake, and running a heat exchanger so that "raw" water is not used into the engine.

Plus this head isn't native to the block, so the coolant passages I'm thinking of using are a little DIY anyway...

OH!! I read an article on a similiar buildup, oughtta be pretty mean Are you keeping the stock water pump and charging system?
The article I read used a remote WP (maybe a Toyota?) and a basic delco alternator, according to the article there can be rectifier overheat problems and seal leaks dumping coolant into the oil sump with the stock system.
?? Got a build sheet with some pricing info?
One of these in a fenderless T three window would be interesting. .. and my youngest turns 30 in four years. hmmmmm.........
Naturally I'd be more comfortable doing one of these engines if I knew someone that had already done one.

_________________
"There are times when a broken tool is better than a sound one, or a twisted personality more useful than a whole one.
For instance, a whole beer bottle isn't half the weapon that half a beer bottle is ..." Randall Garrett

stock OE Mercruiser internal water pump, basic compact Denso alternator.

Pricing is... I'm single, making good enough money, turning 41 next few weeks. I bought nice stuff. New aluminum flywheel, brand name internal parts, etc, etc, etc. I could make almost to the exact HP number, the same power with a low mile 4.8L LS truck motor from a wrecker at around 20cents on the dollar.
I hate the sound of V8's, and I wanted something sort of vintage.
My end result when at some point the veh this is going in gets too rusty or get into an accident, is a scratch built small sedan. I did a 1/25th clay of it when I was 14...27 years later that clay still looks good to me. A feel of it being an evolution of a early 60's Brit design, perhaps something that could be mistaken as an experimental Ferguson roadcar (being AWD).
It needed to not have an LS engine, period.

Please excuse a dumb question from a cooling system simpleton, but isn't the thermostat the actual "warm up circuit" mechanism? That is, when it's closed, no water (or maybe very little water) flows through the radiator and when it warms up (180 degrees?) the thermostat opens substantially and the full cooling circuit is then working.

With my donor, the heater core in and out connections are just two hose connections without valves at the back of the intake manifolds. It looks like water circulates through the heater core all the time and it's doors on the heat/AC ducting that controls whether air passes through to heat the cabin or not.

What will your second warm up circuit do for you?

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886

There should always be some water circulating to prevent hot spots and pump cavitation. That is why an engine will have a bypass hose or a small hole in the stat where the heater core is controlled by a valve that shuts off all flow through the heater core OR a heater circuit without a control valve but with restricted flow.

As a side note- it should also be noted that there are two ways to modulate heater output- up until the early 80's it was typical to control water flow. After that, manufacturers found it better to design the heater core to have flow through at all times, and route the air to bypass the heater core for the cool air requirement. My vehicle has the latter.
Also as an aside, Volvo b18/b20 have no pump through of coolant in the block- only the head, and they had very low rates of bore wear and very effective cooling systems.


Miatav8- so by your diagram, you agree anywhere on the water pump inlet housing (I got used to a hayseed term of "waterneck"), would be fine to return from the heater core? I have bought a Fiat thermostat and some hoses to fit it already, so want to concentrate on where I can have a boss TIG'd on.

Yes, I agree. You could also just use a short piece of exhaust tubing spliced into the hose between the stat T and the pump inlet, then weld a piece of 3/4 tubing to it to use as the fitting. Antifreeze in the correct ratio keeps the exhaust tubing from rusting but you need to paint the outside.