The Stovebolt Site Forums The Shop Area Engine Shop 1957 GMC 347 heater hose and over heat help

Couple things needed help with.
1. Looking for a hand drawn or OEM schematic of the heater hose connection and routing for 57 GMC with 347 engine. Rebuilt original heater box and will be ready to install soon.
2. Over heating. Fresh rebuilt 347, new champion radiator, rebuilt OEM water pump, no heater core connected yet, new180 deg thermostat (verified it opens on stove heat), new hoses. Truck hasn't been on the road yet. Over heats at after 10-15 idling. Tried burping system. Coolant doesn't go down from burping funnel, just rises a couple inches. Drilled hole in thermostat. Tried rubber glove expansion for head gasket issue. Checks ok.

Next step I guess before removing water pump is to hook up manifold heater hose to see if coolant shoots out. Anyone have some advice? Thanks

The heater circuit is not required for proper cooling of the system. I ran an in-line shut off valve in my '57 347 for years. Always left it turned off in the summer. And the heater was an option. If you didn't have one the connections at the engine were just filled with pipe plugs.

Don't be offended by the following questions.

Is coolant actually circulating when the engine is hot? Does the upper radiator hose get hot?

Is the engine fan on backwards? Some dummy that looks a lot like me spent many hours troubleshooting that problem.

Is the engine fan either reasonably close to the radiator or installed properly in a shroud to make sure that it actually pulls air through the radiator?

Were the cylinder head water tubes (either brass or stainless) put back in the heads after the rebuild? Larry Gorden (a knowledgeble tech advisor for early Pontiac V8s like your 347) has posted a short article here about the cooling systems on these engines.

Thanks for the reply Bill. No offense taken. Thats why Im here asking for something Im missing. Understood on the heater. I wont hook it up anytime soon.
I couldn't tell if water was circulating so I just removed the intake plug and installed a heater hose off the intake next to the thermostat and do not get any coolant pushing out in quantity. Small to no stream coming out. Removed water pump, looks to be in great shape (rebuilt OEM) with correct rotation impeller installed. Good fins.
I believe the OEM fan can only fit one way to sit flush on the water pump flange.. Fan is about 4 in from radiator using the OEM shroud.
Brass tunes were reinstalled back into the heads.
Thanks for the link. I do have that sight saved to my favs.

I'm getting concerned I may have a clogged passage in the block.....freshly built. If I try to flush with hose to verify no clogs, I'm trying to figure out where I would connect water feed and where to check output flow that it circulates the entire system

The 4 bolt water pump impeller had at least 3 designs (not counting the one with shorter fins for the 61-63 Tempest), all designed to rotate the same way. I've never seen an actual reverse rotation early water pump and I don't believe there is such a beast. I think this rumor was fueled by the fact that one of the national FLAPS (I think it was NAPA) had the stamped impeller water pump marked as "reverse rotation" in their computer system. I ran one of the pumps with a stamped steel impeller for many years on my '57 347 with no adverse effects. I can back this up with a bunch more data and opinion if you need it.

As shown in the diagram on the link to Larry Gorden's web site above, all coolant is pushed from two different outlets on the water pump into BOTH heads, then down through the block (assuming the thermostat isn't open yet) and into two small (1/2" or so) outlets from the front of the block and back into the water pump intake on the timing gear cover.

Once the thermostat gets warm enough and opens, the majority of the coolant in the heads exits through the upper radiator hose while a smaller amount continues to return to the water pump through the two 1/2" holes on the front of the block, cooling the block. The coolant that exited through the upper radiator hose goes down through the radiator, gets cooled and returns to the large inlet port on the timing gear cover to start the cycle all over again.

I've never seen a 4 bolt Pontiac (GMC V8) water pump that didn't have the impeller pressed on to the proper height (later Pontiac 8 and 11 bolt pumps were notorious for it being wrong), but if the impellor is too far from the hole in the middle of the chamber the pump mounts into the pump will become very inefficient and produce little coolant movement. I'll look up the dimensions later when it cools down in the garage.


Seems strange to me that this engine's system is designed as two parallel systems except for the water pump, radiator and radiator hoses. So a single clog preventing coolant flow would need to be in one of those places.

If I wanted to check for clogs I would:
1. Remove the thermostat and re-install the upper radiator hose.
2. Remove the radiator end of the upper radiator hose and point it somewhere harmless.
3. Remove the radiator end of the lower radiator hose and attach your garden hose to it with duct tape or something similar.
4. Turn on the hose.

You should get a strong flow of water out of the upper radiator hose.

.. and just in case you have to take the timing cover back off again AND you already haven't done the modification check here for a needed modification that will keep your garage floor happier.

I'll be glad to loan you the alignment tool. If you use it you will be around the 14th or 15th to do so.

I had an Econoline van in the shop with an overheating problem that I scratched my head over for days. It turned out to be the rubber bond in the crank pulley had failed so the fan, pump etc turned enough to make me think all was well but not fast enough to cool the engine. Don't know it Pontiacs of old could suffer a similar fate but I've seen it on Chevrolets.

Dimensions on how far to press the impeller (and fan mounting flange) onto the water pump shaft can be found here.

Happened to me a few months ago on the '66 Mustang. Didn't overheat but created hot spots that cooked oil in certain places in the engine causing crusty deposits to circulate around the block and clog the oil pump.

fly4,

Adding a bit of "non-ferd related" info I could find online referring to your 347 and possible water pump question/concerns.

Check out this older discussion with some excellent pictures about potential water pump concerns as this info seems to be directly related to your reported overheating problem. Understand that is old, being from 2012, but thinking maybe still relevant to your problem.

Just my $.02 worth, but in reading that discussion and looking at the pictures, it would appear there is a big difference in potential water circulation capacity between the 2 displayed pumps.

Maybe compare your current pump to those pictured to see if you may have the one with very minimal pump vanes.

I also read several comments in various places about having "Proper clearance between the water pump divider plate and impeller is probably the #1 culprit of hot running Pontiacs. Locating a proper pump with the cast-iron impeller and ensuring the plates run tight without touching (experts can supply the clearance, .040 seems right though) maintains the pressure and the flow through the engine.".

Am interested to hear back on details of your water pump and any resolution you may figure out.

Dan

The pump on the right in the Jalopy Journal thread above is for a 4 cylinder (half a Pontiac V8) 61-63 Tempest.


The "divider plate" was never used on the 4 bolt (pre-1964) water pump design. It was used on the later 8 and 11 bolt water pumps.

I ran across a really good explanation of fans titled "Improving Fan Systems Performance" by the US Department of Energy while doing some research at work years ago. I realize that this article is speaking to fans and air, but a fluid is a fluid and I see no reason it doesn't apply to water pumps as well. It discusses four types of Centrifugal Fans, which is how a water pump operates. They are Airfoil, Backward-inclined, Radial and Forward-curved. Some of them look "backwards" to dummies like me, but they all have advantages and disadvantages explained here starting on page 23. Fan types

Finally back on the project. Thanks for all the input. Great info!

I'll provide an update after more troubleshooting today.

After capping off different ports and using a garden hose, I'm pretty sure I have flow thru my heads and engine block. Water comes out the two block drains and thru the heads. I removed the water pump and it also comes thru the ports. What's difficult to tell is if the water pump is moving enough water. After reinstalling the pump, I look in the thermostat opening and see some movement back and forth. I think that is due to the water coming from both heads and converging there, as the diagram depicts. I reconnected everything and did a test at my radiator for exhaust gas in coolant. The liquid turned green indicating exhaust gas is in coolant. So now I guess I'll do a compression check to see if there is something going on. This is a fresh overhaul with rebuilt heads and new gaskets. Could be an issue but I don't know how thats possible. I'm still not convinced the pump is moving enough water. I don't know how to determine the right flow. The overhauled pump is correct by comparing to the old one I removed and the pics you provided.

Thanks. I did take a look. Seems ok

Interesting read. I have also noticed differences in pump impellers for sale for the 347. I believe I have the right one after comparing to my old one and reading articles and comparing to the pics / info I have from Bill Hanlon. My test kit turned green when checking for exhaust gas in coolant so I'll do a compression check next.