Reproduction Parts for 1916-1964 Chevrolet Passenger Cars & 1918-1987 Chevrolet & GMC Trucks


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well too the 1929 for another shakedown run, keeping them to under 30 minutes and 10 miles. this one was 15 minutes and around 7 miles round trip. Flat land, one small overpass.

today was a beautiful day, cool temps around 75, nice breeze blowing, low humidity. A near perfect day.

took the car out for a run, and about 5 minutes down the road there is air in the Gano, i can see it clearly while cruising steady at any speed. 15, 25, 30 !! then when i stop i can see it burping up. a wave of air bubbles, break air bubbles, etc... over and over while sitting only for a minute. take off and can see the air bubbles in the coolant, does not matter that i am slowly accelerating or not. coolant level was just above core in radiator. stopped and check temps, return line is about 170. top of radiator is around 180-190 bottom is around 150-160. cylinder walls read around 200-215.

get back home and park in driveway, and air ensues, same as when i was driving.

1929 Chevrolet International AC - Engine Shakedown 3 19 Jun 22


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May be a dumb question but...

Are you sure they are AIR bubbles?
Could they be STEAM bubbles from a small hot spot somewhere?

You wouldn't think you would have that much air going into the coolant after you shut it down.


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90+% of the time bubbles in the coolant are air in that gets sucked past the water pump shaft. It is much more common on non pressurized cooling systems. Combustion gases make up almost all the remaining percentage of bubbles. Any steam that might be produced on a hot surface fairly quickly gets mixed into the coolant and condenses back to liquid as long as the bulk coolant temperature is lower than the boiling point of water.

As I have written numerous times the water pump produces pressure in the coolant passages from the pump to the radiator. Once that pressure is reduced by a reduction in engine speed the size of the bubbles is increased resulting in expulsion of coolant. Also the bubbles tend to rise to the highest places in the cooling system so more likely to pass by the Gano filter.

In this case tightening the water pump packing or replacing some of all of the packing should stop or at least reduce coolant loss.


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I may be wrong but I think I remember Jerry posting somewhere that he has the FS sealed non greasable water pump.

Last edited by m006840; 06/19/22 09:43 PM.

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Just because you have a sealed water pump doesn't mean it can't leak air. The seal is primarily designed to prevent water leaking. Also the hose connection, particularly the lower hose can leak air even if it doesn't leak water.


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yes it is the newer style TFS water pump with seals. i will go back over and retighten the screws on all clamps, and check all connections.

checking the coolant after i parked, showed the coolant was down 1/2 gallon. was full when i pulled out. always check it on they way out and when i return (hot & cold)

the car runs great, fires up, idles, accelerates, etc... even after driving it i can shut it off, and fire right back up, or wait 5-10 minutes, and fires right back up.

was wondering could the timing cause it to run hotter than it should ?
Points: .018"
Spark Plug Gap: .040"
Timing: around 15-18 DEG BTDC (tweaked by ear and engine smooth idle no sputter from tail pipe)
Float Level: .75"


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Losing 1/2 gallon of coolant should be of concern. My guess is that exhaust is getting into the coolant.


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Any steaming at the tail pipe? Try overfilling the radiator and start the motor. Look for the bubbles. If you don’t get any at idle, keep increasing the rpm’s until you get bubbles. Keep checking the radiator to keep it full to the top. Just make sure your not pulling air from the radiator. I know my 31’s happy water level after driving a lot is down quite a bit and might be close to a half gallon from completely full but I’m not sure. I do know that I add water and when I do,it seems like a fair amount. Try putting a temporary overflow tank on your overflow pipe to see how much coolant is getting pushed out. If it corresponds to what you need to put in then you’ll know that it’s not going out the exhaust. You can also buy an additive for the radiator water that will show combustion in the water. A combustion leak will push water out, cause bubbles, and overheating. You can also pull the plugs again, look at the electrodes and do another compression test. Things like this abs suck and really get my mad. Do everything by the book with the best parts, sealants, etc., and still the BS. Good luck.

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well ran out to lunch today for work, and made a trip to Harbor Freight ;!

picked up a few items i needed, also picked up their Maddox Combustion Leak Detector and BLOCK-TESTER Combustion Leak Detector Fluid will see what it shows on the 1929. read reviews on it plus videos. seems to be a good viable test system.

last night i went out and checked all the hardware on the coolant lines and water pump, made sure everything was tight. did not go out and wrench down everything to break off screw & nuts :)

also plan to run the test as Noted by Ted above. i am will to spend the time and check and recheck before tearing down and breaking down. been there done that once already!!


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Just an FYI regarding hose clamps. The original style wire type would not seal on the reinforced hose that I used on my 32. It did not leak but did allow air to enter and I ended up using modern worm gear clamps. I never gave it any thought as working in a heavy truck dealership I used what we sold for the trucks which is way thicker and heavier than the original automotive hose.


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ok so i ran a few test last night... mainly with the Combustion Leak Detector.

Fluid is Blue and if exposed to combustion gases it turns Yellow (for Gasoline Engines)

First Test was to see if the Fluid Changed Colors in Ambient Air, only sucking in air around me. car is not running, nothing is going on or anything else running.

https://youtu.be/igtbAa7MsNA 

Nothing happened fluid stayed blue


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Next was a test to see IF the fluid would actually turn yellow if exposed to exhaust gases, so started up car and ran the test so it would suck in the air from the tail pipe. 



fluid quickly turns yellow, so we know the fluid works


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So next up was true car test. fired up car, let it get up to around 140-150 coolant temp and them ran the test, i used aa silicone funnel to seal around the radiator fill neck and the base of the tester. not 100% fool proof but the silicone funnel was snug around both.

https://youtu.be/5FgXPSr62JY 

fluid stayed blue. had a slight green tint, but i pumped air for over a minute and never changed.


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seems like no exhaust gases are getting into the coolant, but no guarantees.


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I ran the test on the car twice, once after idle warm up and then about an hour later after another warm up.

same results


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Took car out for a test drive today, was a short trip about 1.5 miles nothing over 30 mph maybe 10 minutes. Clear Sunny afternoon, temps around 85F 50% humidity. coolant level was just over the core. car fired right up, let it idle for about 10 minutes.

about half mile or so in, started seeing the bubbles in the coolant via the Gano. as i drove more more bubbles arose. pulled back in driveway, ran the combustion check (engine still running bubbles running as well) fluid stayed blue.

When i cut the engine off bubbles erupted and puked coolant out the overflow. dumped about 1/2 - 3/4 gallon on the driveway. laser temp on radiator was around 200F at the top. 

seems to tell me it is overheating, and should not on a short trip like this one. 


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What was the temp at the bottom of the radiator? If it is dropping 40 degrees or so it tells me the radiator is doing its job. My next step would be to advance the timing until it pings and then back off until it does not.


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I doubt if a low compression ratio 1929 could get close to pinging with todays gas.


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figured i would go back check everything... start at square 1

pulled all the plugs, and checked gap & coloration, they all were set to the .040" i set them to per VCCA recommendation, and they all looked really clean 

did a compression test on all 6 cylinders, and got around 65-70 on all cylinders.
​​​​​​​

Attached Images
20220626_103607 Spark Plug 02b.jpg 20220626_111833 Compression Cyl 04.jpg

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pulled distributor cap, checked point gap, .018" 

spun engine around to cylinder 1 TDC

checked where rotor button was pointing, looked to be a tad off, put it back together and ran engine, and looks like it was sitting right around 5-7 deg of timing !?!? 

so pulled distributor, spun it one tooth, reset oil pump to mate up, and put it all back together.

connected power and fired up car, it sputtered and stuttered. went around and slowly advanced timing, adjusted it till it ran smooth, and check on exhaust. I put my hand near exhaust to feel the output, feeling mainly for the sputter or puff out hte pipe. after about 10 minutes got it idling smoothly. pushed the throttle a few times, revved right up. 

decided to take it for a quick block spin, same 1.5 mile trek nothing over 25 mph. outdoor temps were around 85F and humid.

car ran fine, accelerated smoothly and pulled nicely. I did not see any bubbles, pulled in driveway and cut it off, no burping or puking. ran temps. top of radiator was around 180-185 bottom around 150-155. cylinders walls were around 210-220. fired it back up no issues, and pulled it into garage for the night.

seems to be a little bit happier, and will take it back out for another short trip and run the same tests, then maybe go out for a little longer ride and see how it does. 


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That is good news. I think you have solved your issue.


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while testing and playing with the sideview mirror, i did my second test drive after timing. car started right up, ran strong, good acceleration, etc... temp was 80F low humidity, and at dusk. drove the same 1.5 mile 5 minute trip. when i parked in driveway temp on radiator was around 180F at the top 150F at the bottom. no puking when i shut it off. there is still air bubbles when not at idle, not as bad and only when it warms up.


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