Thanks for the info. Forgot to say earlier, I did retorque the heads and after these overheat episodes, the coolant looks clean with no contamination that I think you would get from an exhaust leak. Ditto clean oil too. I can work my way towards pulling the heads and replacing the head gaskets after checking out these other things. Thanks and I am hoping no rebuild too although I like wrenching. This was supposed to be an easy project ha!

 

To make steam in a 15 min idle is extremely severe:
We used to run cars for 60-90 sec with no water in the block whatsoever. Barely hot.
But to go from there ,to steam, a few minutes later makes me suspect drastic problems.
With no thermostat it should barely warm up in that time.
My suspects:

• severely retarded timing
• reverse rotation water pump
• blocked water jacket
• wrong or blown head gasket

I would check:

• 12* timing at idle is with no vac can attached, then hook it up to manifold, advance is counter clockwise before timing mark, not after. zero out an adjustable light and recheck. some adj lights do not play nice with some ignitions. light should be an inch before timing tab mark. If vac is attached it will jump to 2+ inches. If you are just idling that would be good enough. Run a slipped balancer check and check for true TDC mark on balancer with a piston stop.
• check for good water flow from rad core tubes by looking inside rad cap, or pulling upper rad hose
• open block drain plugs & check for flow, scan block for hot spots with IR gun
• check cylinder heads above all exhaust port for steaming hot temps with IR gun
• check rad for exhaust gas

 

Great advice and Thanks!

I set it for 4 BTDC with vac advance plugged per GM spec.

Will check out all of your suggestions. Balancer might have slipped. Can you check TDC on a BB with a regular dial indicator? Just remembered I do have an empty BB head so I can see how a dial indicator would align.

 

Hello again 20mercury!

I see that our friend LARS responded to you. He has a great paper on "How to set the timing on the engine" to make power. I would ask LARS for a copy and he is a great guy and usually responds right away. The fact your engine has the timing retarded will make the engine get red hot. This problem should be addressed as soon as you can. This might be a major cause of the heat you are experiencing with your engine. Fix the timing and your engine will make mucho Horsepower, the 427 is one of the best engines that Chevrolet ever made in my humble opinion. The stroke and bore are better in the 427 than the 454 for building a high revving engine.

My BB 427 ran very hot when after re-installing the rebuilt engine and it turned out to be a broken vacuum line going to the vacuum advance. While idling in traffic I saw as high as 260* with my cast iron heads and no damage occurred before I switched over to a electric cooling fan. Had I been using aluminum heads they would have been toast. After a new water pump from Stewart along with a pre-drilled thermostat and new aluminum radiator including all new seals around the radiator. I then switched my 427 to EVANS NPG coolant inside the cooling system. It is a water-less coolant and it doesn't turn acid and eat your radiator or engine parts. The boiling point is MUCH higher than water and it uses ZERO pressure inside the cooling loop to work properly. I put this stuff in my engine over 25 years ago and it still works great. I would hate to have to buy the 4 gallons again at the newer prices. The NPG may be excessive for some folks but if you have a heat issue it can save the day.

An electric fan is a great way to cool the engine IF you don't have the factory thermal clutch assembly. I have an assortment of Corvette fan blades, I have used a five blade and it would work pretty well as long as I was moving. The electric fan I am using was made by SPAL and is a dual 11" fan unit with a shroud made for them. It bolted right up on the back of the radiator and covers about 85% of the radiator. For a quiet electric fan system you want to use a PWM Electric fan controller like the one from DeRale that I use. It starts at whatever temp you choose and will start up the fans at 50% speed/power and then slowly ramp up the fan speed if the engine continues to get hot. The DeRale Electric Fan Controller is a good basic unit but now the prices have gone nuts.

I have never had to do anything different to replace the coolant in my 427, no burping or bleeding needed. I fill it to the top of the radiator and then let the engine decide how much coolant it needs by overflowing into a closed container so it can be pulled back into the engine as it cools. An Aluminum radiator is also a good thing to use but the sealing of the radiator is critical to force the air through the radiator. No radiator seals and the cooling will be marginal at best when moving down the road.

Keep up the good work you are doing and you should be driving the car soon!

 

Emissions

 

I do not know if you could use a dial indicator, they are delicate and I am afraid it would bend.
On an assembled block, a threaded stud works well, thru the spark plug hole, just smooth the end of sharp edges, and move the piston slowly.
Pick a spot 20-30* BTDC, then tighten the studs locknut. And reverse it to do the other side.
Two sharpie marks on the balancer and split the difference for TDC.

 

Thanks Leigh!

That is a slick method. Dial indicator worked well for me on outboard motors but i was afraid that the dial indicator might come in at an angle on a BB head
Have not checked yet. Your method is pretty slick. Much Thanks!!!

 

Dial indicator works great with no heads on, then you can go straight down on the piston.
Yes spark plug is at a pretty good angle, maybe 45*.

 

How about driving it so you get actual air through it. Your never going to be sitting in one place with your car idling for 15 minutes plus. Big blocks produce a ton of heat and just sitting there isn't getting rid of any of it.
My big block has 11:1 compression 525hp and running 36 degrees all in with zero issues. I run a 160 thermostat so it's flowing water early. Personally I wouldn't go higher than 180. That's the temp it's openning. At 190 it's starting to open so you are just 10 degrees from 200 all the time. A lower openning temp gets all that coolant flowing sooner. On really high heat and high humidity days when I drop off the highway into stop and go traffic it will go between 200 and 210. Once moving it stays around 185-200. Now that its staying below 70ºF ambient i may put in the 180 t stat so i can have a working heater.
I run twin puller fans with a Dakota digital controller, first fan on at 185, second at 195 if I remember correctly. I used to run a single 16 inch but it was loud and not as effective. I also have a stand-off shroud that covers the entire radiator and has wind flow pass through flaps.

 

I wanted to provide a followup update and say thanks again for all the helpful advice.

Increased timing with vac advance plugged to 8 to 10 BTDC. Still overheated.

I finally gave up looking for my IR gun and bought another and checked temp in and out radiator. Temp was the same....duh....So did a super flush, installed a new water pump and 180 thermostat with 2 1/8" holes. And problem solved. Still runs a little hot at idle IMHO but stabilizes.

So I had planned to install OEM ac with R12 but if i have to install the OEM condener I think I will add electric fans.

Much Thanks again for all the great advice!!!