63 409 overheating & other issues

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smd321

Active Member
Hey guys,

I'm new to this forum. I am working on a 63 Impala with the 340HP 409 ( rochester 4 barrel). Everything is stock as far as I know. This car was my Dad's, and has always had overheating issues since he rebuilt it in the early 80's. I know this is common on the 409's, but I decided to tackle the issue recently to see if I could find anything.

At the moment, it will get up to 210-220 F on an 80 degree day just sitting in the driveway idling. This is without running the front mount electric fan, which takes a few degrees off but the car still idles hot even with it on. I'm running Shell 93, highest I can get. No AC.

So far:
- Radiator boiled & flushed (it had a leak, which is what prompted this investigation). It's a 4 row Harrison
- I have the SBC fan shroud that goes 2-3 inches past the 7 blade fan. Plan to cut this down next time I have to pull the radiator, but as you will see further down, this is now a smaller concern
- New 160 deg F thermostat and new fan clutch.
-Newer Sun temperature gauge.

On cold start, engine warms up to 160 and then you can hear water flow and radiator gets hot very quickly. I haven't pulled the water pump, but it seems like the cooling system is working fine. The car comes back down to 190-200 at cruising speed.

Exhaust heat riser moves freely.

I went after the tuning next. I found that the vacuum advance and mechanical advance are working, but vacuum advance was not in effect at idle because I only had 5-6 inches vacuum. I sprayed around the carb and intake gaskets with WD40 but was unable to identify any leaks.

Then I found the PCV line was hooked up with no PCV valve. The air moving through that was noisier than the air going in the carb. If you pinched the PCV hose, the engine would stall. I put a new PCV valve in, readjusted the carburetor and my manifold vacuum is up to 8-10 inches. Still not very good.

I did a compression test. I have a range of 125 PSI to 150 PSI. Most are 130-140.

I'm planning to check valve lash next in the hopes I can get my compression evened out.

What would you advise? Is it time to get rebuild plans rolling?

Thanks!
Stephen
 
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Don Jacks

Well Seasoned Member
Supporting Member 3
Bump the timing up for now[add about 10 degrees] and see if it helps.With that low of vacuum,that timing chain is streched out considerably helping cause that low of compression reading.Yes,it's likely getting time to rebuild fairly soon. your cam timing is likely retarded due to the streached chain.Bumping the lead up will help cover it up a bit.:welcome2 Fix or replace that shroud,it's hurting you more than you think.
 
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smd321

Active Member
Thanks guys!

Timing chain is making sense... my readings in firing order: 130 140 150 130 135 125 120 130

Any suggestions on where to get a correct 409 shroud? I see some repro but they are pricey. Would rather cut mine down first to see what it does.
 
4speedman

4speedman

Well Known Member
Supporting Member 2
Are you checking the compression with all the spark plugs out and the carb proped open that makes a differance in the readings.I had a overheat problem at one time and advanceing the timing took care of the problem these 09s can take a little more timing than most other engines.And the shroud needs cutting down to the 409 size. And i don't think the 409s have a heating problem i drove one as a daily driver back in the day and it never overheated with the factory 3 core radiator its that we get away from the factory stuff and we have a problem i would think that gm would not have made a differant fan shroud for the 409s without a lot of testing than said it needed to be done
 
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427John

Well Known Member
I agree with Don on the ignition timing and checking for chain stretch,late timing will reject so much heat out the exhaust that your underhood temps will get high at slow or no speed and that never helps with coolant temps.If the timing chain does show signs of stretch,since it is doable with the engine in the car,I would change it then re-evaluate.If changing the timing chain and verifying proper adjustment of the valves improves the compression readings and your satisfied with power,economy,and other attributes of the engine ( no smoke,major leaks etc.),I would tend to believe that the engine is sound.If your underhood temps are excessive I would be looking at late ignition timing and/or excessively lean idle mixture.I consider underhood temps to be high if I shut the engine off get out and open the hood and stand in front of the car with my legs touching the bumper and leaning slightly towards the engine compartment,if you can feel heat radiating onto your face and arms not due to a breeze blowing it onto you to the point you want to step back,your engine compartment is too hot.Another visual clue would be is if at night you can see any glow from your exhaust manifolds with the engine idling you have late timing and/or excessively lean mixture.
 
4speedman

4speedman

Well Known Member
Supporting Member 2
When i did have the overheat problem that advancing the timing fixed the headers would glow red you could see this when the rpms were brought up this was easy to see a night
 
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smd321

Active Member
Thanks guys. Based on this advice, I will pull the radiator to cut the fan shroud down and replace the timing chain. I will let you know what I find!

While I'm in there, I will inspect the water pump. Does anyone know what the difference is between the various water pumps or how to identify them?
 
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Don Jacks

Well Seasoned Member
Supporting Member 3
Not a bad plan,but you may be getting ahead of your self.Slow down and test this thine one step at a time.First,with the engine warmed up and the vacuum gauge attached,advance the timing 10 degrees and note the amount of vac increase.Drive the car,does it ping?,does it run cooler? If no on the ping,yes on the cooling,advance it further by at little and see if it improves further.Let the engine cool down some,bring the timing mark to zero then rock the balancer back and forth just enough to feel it take up the slack in the chain.If the slack exceeds 4 degrees,the chain is dying.
 
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smd321

Active Member
Too late! I've got just over 1/2" slack. Seems pretty sloppy but not enough to cause the range of compression readings.

New chain and gaskets will be here tomorrow. I'll cut my shroud down tonight and then assemble it tomorrow. If this doesn't help, then I'll start coming up with a rebuild plan... I have an extra 409 short block and a dual quad setup for it, so maybe I will go that route. I don't have the 4690 heads tho.
 
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427John

Well Known Member
smd321 said:
Thanks guys. Based on this advice, I will pull the radiator to cut the fan shroud down and replace the timing chain. I will let you know what I find!

While I'm in there, I will inspect the water pump. Does anyone know what the difference is between the various water pumps or how to identify them?
Click to expand...
While some car makes did offer std and hi flow pumps for a given engine family I don't know if chevy did,there can also be variations on aftermarket rebuilds.The cheapest pumps will typically have a little stamped steel straight vane open faced impeller while the very best may have a large cast curved vane closed faced impeller.These attributes all contribute to higher and more consistent flow,unfortunately they will be hard to see without removing the back cover or using a borescope.If the supplier is really proud of their pump they may list these in their product description.External differences will be few,and the housing will usually be cast to accept a large impeller even if a small impeller is used.Even if a large cast impeller is not available,attention to detail on assembly of the pump can increase performance,keeping the clearances as tight as possible between the vanes and the volute surface and closing off the back or keeping clearance tight to the rear cover will increase flow.There used to be pumps and impeller kits marketed by an outfit called flow cooler that was a plate rivetted to the back of the impeller to close it.I don't know if they're still available but would be easy to fabricate if not.Keep in mind doing something like that may require balancing.
 
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Don Jacks

Well Seasoned Member
Supporting Member 3
When you replace the chain,before you button it up,do another compression test and notice how much higher the reading is.1/2 inch of slack means that your cam timing is going to be very retarded[likely more than 10 degrees] which will drop your cranking at least 20 psi,maybe as much 25 psi.If the cranking compression is still low,yank the "Bit@h" and prepare for a rebuild.
 
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smd321

Active Member
So I've got my shroud cut down to what Jim shows. I was cleaning up the gasket surfaces getting ready for when my parts arrive and I noticed that my water pump (casting 3850145) has outlets that are a lot smaller than the mating surface on the block. You can see the shadow in this picture. Is this correct?IMG_20200706_211432 (1).jpg
 
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smd321

Active Member
Well, the good news is that it will be fun to do a rebuild... The chain didn't make much difference. I'll go foraging in the garage to see what parts I can find and maybe start another thread. Thanks for all the help!
 
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Jerry B

Well Known Member
About 20 years ago I had a heating problem with a 409 - 409 with about 2000 miles on it after an overhaul. I replaced the 3 core with a 4 core reproduction radiator, rebuilt the water pump including a new impeller, blocked off the heat passages in the intake manifold and replaced the fan clutch with a spacer. Not much help. Changing from 10-40 oil to 10-30 and running distilled water, 15% antifreeze, and water wetter made a big difference.
 
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