Good afternoon

my 66 327/300 has been running hot at idle. I've been through everything on the board (timing, fan clutch, engine/radiator flush). Only things I haven't touched are water pump and radiator. It's fine at speed so I'm thinking not the radiator.

I was looking at water pumps at Advance Auto - they have everything from a $40 to a $200 one. I'm sure the higher $$$ ones push more coolant but I'm not sure they're worth the cost difference. I'm not worried about originality for judging.

What do y'all use? Anything to know? My car has had a little bit of work done (heads, intake, carb, cam and headers) but it's not drastically modified.

I'd appreciate your input.

Thanks
Bryan

 

There's absolutely no need for any of the "whizbang" water pumps - the stock water pump will work just fine, and the water pump is hardly ever the cause of a cooling problem (unless the fins on the impeller are corroded away).

Can you define "running hot at idle"? Have you checked it at the thermostat housing with an I.R. gun so you know what the temp gauge is really telling you? Does it "puke" coolant out of the overflow hose when idling?

"Running hot" at idle is almost always either an airflow issue (radiator not sealed to the support, shroud not sealed to the radiator, fan clutch worn out) or an ignition timing issue (initial timing retarded, vacuum advance not working or connected to the wrong vacuum source). Check these basics before tearing into the water pump. See my feature article on cooling in the current (August) issue of "Corvette Enthusiast" magazine.

 

Usually pumps are replaced when they start leaking ( overflow hole) Try previous suggestions. NAPA has replacement in cast iron at about $80. I replaced my original on 63 swc (340 hp) with one from them works perfectly. painted it corvette orange. good luck Abe G

 

Brand new pumps from GM aren't much different in price, and last much longer than aftermarket. Price one from a Chevy dealer.

Good Luck!

 

Hey, I'm Bryan's brother and have been working with him on this as well.

My initial thought was same as yours that it should be an airflow issue. Fan clutch is working fine and I can assure you that it is pulling air BUT I'm not sure about "sealing" the shroud. Does anyone have pictues of what you're talking about here? There does seem to be more space than I would expect between the fan blades and shroud.

Regarding what actual temp is, that's something that needs to be checked but the temp gauge should still be good for measuring a "trend". Driving it is stable around 180.. at idle it just keeps going up (I turned it off when it hit around 220 or so).

Timing/vacuum has been set. We did put a new vacuum advance module on the distributor as the old one was done for. We also found that the car was running about 2degrees retarded at idle. It is now I think right at 10 advance. Also adjusted the carburetor idle mixture to be sure it wasn't too lean. After all this the car did run much better, but temperature trends were the same.

The only thing left I could think of was the water pump. Dad and I rebuilt a 1955 Jag and chased overheating issues in it forever. Finally got around to the waterpump, pulled the old one out and the housing was internally corroded so that the impeller/housing clearance wasn't in spec. This just seems possible in Bryan's case since at highway engine rpm (2000+) the impeller clearance isn't too critical, but at idle (800rpm) it may struggle. I'm taking a class in automotive engines right now and asked my professor what he thought could be a likely cause and he thought based on what I told him that water pump sounded the most likely as well. Plus it's one of the cheaper things to replace and hasn't been done in at least 25 years anyway.

That said I would like to see pictures of an in-spec shroud and fan on a 327.

 

If the water pump is that old, I would replace it regardless. it will be the next thing to go out on you. New Napa or GM, stay away from cheap rebuilds.

You should have about 1/2" clearance, maybe 3/4" between fan tip and shroud, fan should be half in and half out of shround.

Sealing around shroud: Visually look for gap at sides especially where air can bypass radiator, top and bottom also. I used round pipe insualtion dropped along the sides for my C1 sealing, I am sure you can come up with something, 1/8" thick rubber strips and pop rivets would work.

Doug

 

you mentioned you replaced the vacuum advance cannister, are you sure it's the correct one for your motor based on the vacuum level your motor makes at idle? Is it hooked up to full manifold vacuum source rather than a ported vacuum source?

You also say the fanclutch is pulling air but have you tested it by letting the motor get up to operating temp and than shutting the motor down? If the fanclutch is good it should stop between 1-3 revolutions. It it takes longer than that or just freespins it's bad and needs to be replaced.

The waterpump in my '65 is the original unit and it still works great.
I don't pretend to know a lot about waterpumps but IF there was an issue with the waterpump wouldn't it show up more at highway speeds rather than idle? At idle it wouldn't have to pump as much compared to higher RPM's so I would think (but could easily be wrong) that if there was an issue with the unit it would show the symptoms in reverse than they are in your case.

 

Couple of quick pictures of the fan & shroud. Far as I know it's all original. My dad bought it in '79 from the original owner. he didn't replace it.

We did test fan clutch. It stopped shortly after cutting off hot engine (2 rotations and was tight to spin). Vacuum cannister was from Advance and for '66 Corvette. It is connected to carb. It is pulling vacuum. It was not, we replaced it. Fan clutch was replaced about six months ago as well.

Thanks for the suggestions. My brother was more involved than me with timing and vacuum work. I'm not quite sure what they were doing with that. I'm sure he'll chime in again.

 

That definitely looks like more than 1/2-3/4" clearance between the tip of the fan blades and shroud. Perhaps that is part of the problem.
Maybe DPO did something before dad got it??

Re: vacuum advance module. It should be the correct one for the car per advance auto computer, however as far as full manifold vacuum vs ported, we didn't have a vacuum gauge to check this. There was suction on the vacuum hose coming off of the carburettor, but the engine did not stall if it was disconnected. Did get a tiny bit more advance with the module hooked up though.

water pumps are more efficient at higher speeds in this case. The example is that if there is a small clearance problem at a low flow right (low rpm) this could be a large percentage of the total flow. As the flow goes up the percentage of water NOT pumped gets smaller. Plus, i'm a little fuzzy on the exact math here, but i'm pretty sure that centrifugal pumps aren't neccissarily linear with speed.

 

Doesn't look like you have any shroud/radiator gaps.

What is the fan diameter? The correct fan should be about 17.5" diameter

Do you have the same clearance, on bottom as on top?

If you can connect to manifold vacuum via a manifold port, that would guarantee manifold vacuum. Not sure of your carb, some carbs had ported and manifold vacuum ports. I cannot tell you which is which. You need a vacuum gauge. Go buy one, they are invaluable tuning tools for setting idle mixtures, diagnosing engine problems like leaky valves, bad rings, etc.

Doug

 

Also looks like the wrong fan clutch, too short, fan not far enuf forward.

Doug

 

Doug is right. The fan blades need to be half in-half out of the shroud. You can buy a spacer to move the fan closer to the radiator and that will make a huge difference.

I bet if you put a piece of paper in front of the radiator it won't stick, and it should.

 

We could not find any vacuum fittings on the manifold. It is a GM manifold I believe from a 365HP 327, although it may have been from an early LT1 350?

 

it has the oil fill tube in the front of it so it's a 327ci intake, not one from a 350ci.
vacuum fitting would be on the carb. if it pulls vacuum at idle it's a full manifold vacuum source fitting, it it doesn't pull vacuum at idle but does ABOVE idle speed it's a ported vacuum source.
If the carb only has a ported vacuum source you can drill and tap the intake for a fitting, available from most of the major parts vendors such as Paragon, to get full manifold vacuum.

also, you mention that the new vacuum can you bought was listed for a '66 Corvette but there were different motor configurations in '66 and took different vacuum cans. Again, are you SURE you have the correct one for your motor. forget what the auto parts store computer says, get a vacuum gauge and measure your vacuum at idle to get the correct vacuum can.

BTW, you say it's a '66 327/300 but the valve cover in your picture shows a breather on it. is that simply a wrong valve cover or is the motor really a 350ci? The 327ci motors didn't have holes in the valve covers for the PCV system like a 350ci motor did.
It's a bit confusing since you have later valve covers with a breather in one which would be correct for a 350ci but also an oil fill tube in the front of the intake which is correct for a 327ci.

 

It is the numbers matching 327 engine. The valve covers are aftermarket mickey thompsons. Dougs headers, holley 650CFM double pump carb, camaro z28 heads, and comp-cam. I think that's all that's non-stock about the engine.

 

i am a newbie at this but what i see, is that fan is to small for the shroud
or vice versus. also it looks (could be photo angle) the fan needs to go farther into the shroud. if your carb has two vacuum ports use the lowest
one close to the manifold. hope i am right jim

 

i agree wit the above posts.

fan may be too small in diameter.
fan is definately too far back
holley 650 DP should have a vac advance port on the throttle plate under the front metering block/bowl pointing towards the pass side at an angle.

 

What's the total measured timing at idle? Also, what kind of vacuum readings are you seeing on the hose that goes to the advance can at idle?

Thanks,
Brian

 

Chances are you have the wrong vacuum can if you bought one for a 327,300hp. If you have a after market camshaft,it could reduce your vacuum considerably. You MUST know how much vacuum you have at idle,then post your results along with your vacuum can number.

 

Total adv. at idle was 10 degrees I believe, maybe 12 with vacuum attached.