The Stovebolt Site Forums The Shop Area Engine Shop Cooling the GMC inline

I need a little help on the cooling system for the GMC inline engines. I am putting a 302 in a 52 1/2 ton P/U and want to use the original AIR FLOW heater (with the temp control valve on the firewall). The 302 that I have came with the special fittings that come off the thermostat housing and the waterpump for coolant bypass (connected together with the short section of hose). My question is this:
If I leave the special fittings installed and connect the heater hoses to them, will my heater ever get warm? If I do not install the special fittings and connect the heater hoses directly to the thermostat and water pump (I think this is the most commonly found setup), will the engine still warm up properly or will I have hot spots and head warpage?
This is assuming that the heater control valve is off and not letting any water into the heater core to recirculate to the waterpump(summertime). During the wintertime water would be allowed to recirculate because the valve is open.
I don't remember seeing the special fittings on any of the 228 or 248 engines. Does the 302 need these fittings for recirculation because of the bigger c.i.d?
Any ideas or thoughts on this would be great and if the question needs more clarification let me know.

There are a few 302 experts on here, but the one that comes to mind is Proffit, and he is away on vacation in Italy or someplace. Somebody should be able to answer your question- it just may take a bit. Good Luck.

I'm not sure I understand the question entirely, but the fitting on the side of the water pump, and the fitting on the side of the thermostat housing base are the pressure and return line connections respectively.

If your question is will the heater warm up if you leave the by-pass in place, the answer is "some", but not much.

The bypass you describe is just a routine by-pass for a truck that doesn't have a heater. If you can snap a photo and email it to me, as the old saying goes a picture is worth a thousand words.

Sounds like you have a normal setup for no heater. The by-pass, in my opinion, would have zero effect on cooling because it is all under the thermostat itself. Whether you are by passing 6" or 6' through a heater core is immaterial to my thinking.

I have the bypass and intend to dispense with it when I replace the water pump. One point to note is that the original heater thermostat is fairly restrictive compared to the aftermarket on/off ball valve so if you use the bypass you may be further limiting flow through the heater. The gmc parts manual lists a fitting to block the bypass when installing a heater so I would venture a guess that it isn't all that important.

Good info! I think I'll just dispose of the bypass idea. I have the fitting that GMC made to block off the bypass when you added a heater. I assume that this was the fix instead of just removing the bypass all together and connecting the heater hoses directly to the water pump and thermostat housing. On a cold winter day I'll want the heater to work to it's max capacity. I'll try the engine setup without the bypass and if it don't work I'll put it in. As always, thanks for the info and any more tips are appeciated.