Originally Posted by rich weyand (Post 7582507)

OK, here's my take.

I think the guy with post #2 is the most correct.

Basically, if you have a system that is a loop, and you put a valve in it (in this case, the thermostat), then when the valve is closed, nothing circulates in the loop.

With me so far?

OK, so that's not a good thing. So the General built a second loop into the system, by installing a bypass that runs from the output of the water pump back to the engine, circulating coolant in that loop even if the valve is closed. So all the valve controls now is shutting off the radiator. But coolant still circulates, avoiding hot spots.

They didn't build this bypass into the Vortec heads for some reason (weight? the location already in the block inconvenient?), so you add it externally.

Now, lots of SBCs run pretty cold, like mine. Low compression, torquer cam, runs cold as a witch's heart. So I took out the always-on mechanical fan, and added an electrical fan which hardly ever runs except at sitting (no air flow from movement) on a hot day.

So a guy like me, with that setup, doesn't know about the bypass line, say, so he doesn't put it on. No problem, because his heater circuit sort of acts like a bypass, per the later posts in the thread.

But then some guy comes along who puts in the Vortec heads, and doesn't know about the bypass line, and cuts the heater out because he lives in Cali, and all of a sudden he is trying to diagnosis overheating issues.

BTW, another thread I found, one poster said the reason for needing circulation when the thermostat is closed is avoiding local hot spots, especially where the exhaust ports are adjacent to each other, to avoid (ta-da!) cracking the heads.

So that's my take.

Originally Posted by rich weyand (Post 7582553)

One other thing you could do. Run the bypass hose with a selector switch in it that can select the heater core OR the bypass. So one selector valve and a T. Then you can have the heater core for the winter, and bypass it in the summer. The one thing you can't do is just shut it off.

What you need is a 1/2" NPT 3-way valve. Search that on Amazon or google. Looks like 30 bucks for a competent one. Here's an example: Industrial Grade 1PZA1 Three Way Ball Valve, 1/2 In NPT, Brass: Amazon.com: Industrial & Scientific

Originally Posted by Valarius_Starchaser (Post 7582555)

We get guys doing that up here and they are also the guys coming in to get their heater core flushed every winter because the lack of flow forms a sludge and makes it work poorly just my .02

Originally Posted by enaberif (Post 7581897)

1) Quit running water! Your truck needs either antifreeze or something like "water wetter" (http://www.redlineoil.com/Products.aspx?pcid=10) if you want to keep using water.

Originally Posted by chevybuldr (Post 7581946)

... Over heat issue might be an air pocket in the cooling system. You need to put the truck on the driveway, make the radiator higher point then the back of the block. Just because water comes to the top of the intake doesn't mean there is not a pocket.

Originally Posted by enaberif (Post 7582963)

Without knowing what those ticks reference in regards to numbers who knows what you are reading.

Originally Posted by SkinnyG (Post 7583056)

I have a 195° thermostat in my truck, and the operating temp is a tick below the first line (1/4 of the gauge).

I have an electric fan, which is switched on at 212°, and off at 192°, and the needle never passes the first line.

My truck is a '77, with original gauge and presumably sender.

Originally Posted by Jake Wade (Post 7582768)

Try bumping your initial timing up to 14º-16º. You have a larger camshaft now and this is a good number.

Your vacuum reading at idle most likely will not be over 16-17 with that camshaft, and that's well tuned.

Originally Posted by Gregski (Post 7583096)

bumped the initial timing to 16* and with manifold vacuum hooked up to the canister on the distributor the engine is set to idle at 850 RPM and it pulls a perfect (steady) 20 inches of Mercury (that is as close to perfect as you can get) I honestly don't see my camshaft as much of a performance cam, its moderate at best

I don't think this will impact my engine running hot (notice I did not call it overheating) but only a test drive or two will tell, and for that we will have to wait until tomorrow

Originally Posted by rich weyand (Post 7583109)

... My gauge now reads just shy of straight up when everything is operating normally.

Originally Posted by Gregski (Post 7583273)

Thank you very much Rich, so we are aiming at West of middle.

Originally Posted by enaberif (Post 7582963)

Without knowing what those ticks reference in regards to numbers who knows what you are reading.