Overheating and hard starting issues on my 69

[C500]

Keen on anyone's thoughts why this is overheating.

Freshly rebuilt 440, 10.2 CR, mild Crower Cam HDP 271, alluminium stealth heads, cast iron exhaust manifolds, Proform 750, CH4B ally intake manifold, brand new Coolcraft 22 inch radiator - 4 core high efficiency, but starts overheating when driving around town, and hot still hot when around 60mph+. Scratching my head. Water in radiator is starting to boil. New thermostat (not sure of the temp... maybe 180).... also leading to vapor lock and hard starting even when only mildy warmed up. Starts real well when cold. All new radiator hoses, not squashed. I notice the bottom radiator outlet is not very round, kinda oval. I'm thinking theres another problem.... 

[Dino]

What water pump, fan, and shroud do you have?

[C500]

What water pump, fan, and shroud do you have?

Factory water pump, stock fan, new shroud.

[Dino]

Just making sure you don't have the pump mentioned in the overheating thread sticky.

[C500]

Just making sure you don't have the pump mentioned in the overheating thread sticky.

Just read that thread, no - don't have the 440 source pump.

[metallicareload99]

What water pump, fan, and shroud do you have?

Factory water pump, stock fan, new shroud.

What's the timing set @ and are you using vacuum advance? Ported or manifold?

[C500]

What water pump, fan, and shroud do you have?

Factory water pump, stock fan, new shroud.

What's the timing set @ and are you using vacuum advance? Ported or manifold?

Not sure on timing... yes vacuum advance. What do you mean by 'ported or manifold'?

[b5blue]

Sounds lean, enlarge primarys any on that 750? 

[metallicareload99]

Ported vacuum source doesn't supply vacuum @ idle. Manifold vacuum supplies vacuum all the time there is vacuum

[John_Kunkel]

What water pump, fan, and shroud do you have?

Factory water pump, stock fan, new shroud.

Clutch fan or direct drive? I know I'll get flak for this, but a weak fan clutch will give your symptoms, yes, even at road sped.

[C500]

hey guys, thanks for the replies. I have a new Edelbrock AVS2 750 thats going on to replace the proform. In terms of clutch fan or direct drive, ported or manifold, water pump... everything there is bone stock from the factory in '69.

[justcruisin]

So many factors in keeping one of these engines cool, here's a few considerations - fresh engine, what are your bearing clearances, was the block cleaned properly, removing all crud in the water passages, timing and fuel correct, clear exhaust. As far as the cooling system goes - those 4 core radiators are thick and require good air flow at idle to remove the heat, ensure you have the correct rotation fan, if running a clutch fan - is it functioning correctly, (bit hard to be sure) pump in good order, non restrictive pump housing, ensure operation of thermostat by testing it out of the engine, no collapsing hoses, well fitting shroud with minimal gap to fan tips.
Mostly, people have issues at idle in traffic, once your moving at speed there should be plenty of air through the radiator, if you are still hot at 60 then there may be an engine issue or water restriction of some sort.
Here is my set up - 26" cheap alloy 3 x 3/4" row radiator, 19" fixed flex fan, tight fitting shroud and a 17" electric on the front of the radiator with a 190 degree thermo switch in the water pump housing.

[Dano 1]

I'll echo some of what the others have said and add my $0.02 since I have a similar setup.

Timing/fuel mixture - If it's running OK I kinda doubt you're so far out to cause a major problem but definitely worth a look. Disconnect vacuum advance and check base/max timing and see where you are. Pull a couple plugs and look to see how they're burning to give a seat of the pants fuel mixture feel. If it's too hard to tell or they're old plugs, throw a fresh set in and check after a healthy ride to see.

Fan - I run a stock style fan and clutch with no issues so it can be done. I agree with John Kunkel, a bad/weak fan clutch can absolutely cause these issues since you need to be moving a LOT of air. The old dollar bill trick would be worth a try, even at idle a dollar bill should be sucked hard against the front of the radiator, if it falls off or just barely holds on, you're not moving enough air. Might be worth the $20 on a new clutch just to be sure.

Thermostat - I would verify function and/or replace. I just had one go bad in my daily driver after 25k miles so they do fail, even today. 180 also seems a bit low, my '69 runs at 190-195 under pretty much all conditions. A thermostat that opens too early allows too MUCH flow through the radiator resulting in not enough heat being extracted because the coolant is just flying through the radiator. Drilling an 1/8" hole can also help with bleeding air, it's possible you have an air pocket somewhere but again, seems unlikely to cause such a severe issue.

Since you said it is a fresh rebuild I kinda doubt there are any major internal restrictions or flow problems. You could disconnect the radiator hoses, remove the thermostat and use a garden hose etc. to run water through the block and verify that you're getting good flow. It's possible someone dropped something in the block when it was being rebuilt or there's excess gasket material or RTV blocking a coolant passage but that seems unlikely.

[C500]

Gents... thanks again for your replies.... the block has been hot dipped, and rebuilt by a reputable engine builder. Thermostat is new, and with small hole to bleed air. The new AVS2 is installed and set up correctly. The engine shop has made a pretty simple diagnosis in the last 5 mins... the engine was overheating due to a faulty radiator cap! the Stant Lev-r-vent .... Glad thats all it was....I'm about to go pick her up, and trial this new AVS2

[b5blue]

Good luck I hope it's 100% now! 

[C500]

Well, just come back after picking it up, and the temp stayed nice and cool, around 170. Radiator cap was the issue. The AVS2 ran like a champ too, very impressed....

[b5blue]

Great news! Congratulations! 

[Dano 1]

That's awesome to hear, glad you got it sorted without too much hair-pulling!