Technical Chevy 327 overheating mystery

Seriously, Sailsman just try the 190* thermostat and advance the timing like I said and you will be OK.

 

My water pump is the original. I considered a new one, but the original does not leak and the vane inside is clean and functional, so I just put it back on the engine.

 

My new distributor springs should be in today. I am open to trying anything...I'll try to make sense out of this whole thermostat thing. I hope my brain does not overheat!

 

The best way to make sense of your troubleshooting results is to only make one change at a time.

 

I totally agree. I have been doing this and that over the past two years trying to solve this overheating problem. Now, I am going to start with some baseline measurements (radiator top and bottom hoses, radiator fins, under-hood temperature, dash gauge rise over time). I will make a plan to try things in sequence, and I think I will start by eliminating the radiator as the problem, then air flow issues, tuning issues, and finally pulling the heads off to clean the cooling passages. I will note any changes in measurements as I go along.

I have a feeling I will eventually be pulling the heads off, but I really hope the radiator proves to be my problem. As friend of mine once said while working on his car, "I am smarter than IT".

 

Does your car have electric temperature gauge or direct reading?



Bones

 

It's an electric

 

If is ain't steaming, it ain't overheating ! LOL

 

Well, Sailsman , I’ll tell you a story about what happen to me about 25 years ago.
I relplaced the short block in my slightly OT four wheel drive Ford 6 cylinder pick up.
It ran perfect, like yours it would push/suck out of the overflow tank, like it should. But, when I got out on the highway the farther I drove, the hotter it would get, stopping just short of “ Hot” on the notoriously inaccurate OEM electric gauges. Never blew its stack, never gave indication of overheating, but did worry me. Drove it that way for a spell.

One day I was checking things under the hood and spotted a ground wire that I had laid along a firewall seam and had missed hooking up!.... Hooked up my rather large ground wire from the firewall/body to the engine.. Never had any trouble with my lightes , charging, or starting system. After I hooked up that ground wire... my temperature gauge read in the normal range and never showed hot again.
I thought I had a possible heating problem for two years and all it was, was a bad ground, my fault during the overhaul!
I see some similarities between my truck and your problem.
Just thinking....



Bones

 

You bring up an EXCELLENT point, sir! I've found that what you think might be too many grounds, might just be enough.

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An excellent thing to double check...…...thanks!

 

That's a good way to get electrolysis of the coolant as well, as the coolant becomes the path for electrical currents to ground. Electrolysis destroys the coolant and creates corrosion problems within the cooling system.

 

caked up "hot tank" powder ?.....

 

+Just a little "helpful-hint"....When you DO get the radiator /block flushed out use..... DISTILLED WATER instead of tap water when refilling the radiator. It WON'T rust!
Warm climate/winter area .....just a splash or two of anti freeze to keep the water pump lubed.
Change it out every coupla years.
Sounds to me like rust-in-the-radiator is your problem.....spring in the lower hose to keep it from collapsing should fix you up.
6sally6

 

When you solve the problem let us know who gets the Gold Star !

 

I hope we can come up with a final, definite cause of the overheating. Yesterday I verified my electrical ground and it is fine. A complete re-wire was part of the rebuild and we added a ground strap from engine to the frame that was not there before.

Also, I made some cooling system measurements of the radiator and engine bay. Attached is a sheet of my notes with the measurements. Looks like the radiator gets a "pass", but I may want to pull it out anyway and invert it in order to get any stray rust particles out, and look inside with the borescope Top and bottom temps are in the ballpark of 10 degrees different, but I was hoping for a bigger difference.

The under-hood temperature was 140 degrees when the temp gauge was reading 220 at the end of my test. This was at rest, at idle at the end of my testing. I don't know the normal range for this temperature.

I checked the spark plugs for indications of a lean condition. What I found was more like carbon fouled and a little MMT fouling. I haven't been able to get the car out and really "drive" it, so I am going to have to say the richness of the mixture is unknown for the moment. The idle mixture screws are only out 1-1/4 turns on my Holley 4150 (2818) and I read that 1-1/2 is normal. I haven't yet been able to detect a vacuum leak. I will verify no blockage in the intake manifold later when I take off the carb.

I think my next step is going to be removing a block drain plug to see what I can see. They are stuck pretty tight, so I may have to work at it for awhile. If I see anything more than surface rust, I will remove the water pump and try some serious flushing-out from all available holes.

 

If your pcv valve is stuck it will make it lean enough to overheat. If you disconnect the pcv and plug the hose going to the carb you can see how she does without it.

Holley pcv port is full vaccum so without a pcv valve or with a faulty one it will run way lean. Plug examination when you're only idling doesn't tell the real story. With the engine running you should be able to make it struggle/die by pulling the pcv hose off the holley.

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That's very interesting. I have never seen a pvc valve on the car, so this could be the answer if it was removed by a previous owner. I looked it up in the factory (1965 Corvette) manual and see that they had a "metered orifice" on the carb crankcase ventilation port, replacing the ventilation valve. It says to clean it at each tune up, but I guess if it was completely clogged, that would be the opposite of what we are looking for (in a lean condition). However, I am going to remove it and clean it, to be sure it is there and in place. Thanks!

 

So maybe it's time to really clarify whether the system actually over heats or not, i.e. coolant is boiling out of the radiator? Or it's just getting to a temp that you're not comfortable with? What is that temp? And what conditions does it reach that temp?

 

OK, so I went back and read the OP:

OK, so that's not necessarily an overheating condition. Are you running 50/50 coolant/water mix with a pressurized cap?

Is it blowing past the cap and turning to steam? Have you pressure checked the cap?

 

It's a good question, to examine whether it is really overheating. Yes I feel uncomfortable with it's current temperature and would not feel confident to take off on a 50 mile ride because it just continues to rise with time. When I first started the break-in after rebuild, it was worse....going to 240 quickly and overflowing the coolant reservoir. The steps I have taken have improved it little by little.....particularly the discovery (and removal) of quite a few rust particles from the top of the radiator cores, adding the electric pusher fan, reducing exhaust backpressure. Currently, when it gets up to 220-225 or higher, the engine starts to bog down and die at stop lights, but it runs okay below that. This is what worries me a little bit about my cylinder # 5 temperature.....could it be overheating to the point of getting tight due to local blockage of the cooling passage? I think a view into the block through the block drain may be telling.

I am running 50/50 coolant and distilled water and a pressurized cap (13 lb). I have replaced but not tested the cap (good suggestion). It seems to be functioning properly (allows coolant out to the overflow starting about 200*) and allowing it back into the radiator after cooling. It is not turning to steam (anymore), but was earlier.

Thanks for your help

 

Reducing exhaust back pressure helps you say... Have you tried to whack the mufflers with your fist to see if there's any broken baffles blocking the flow? You should be able to hear something rattling around in there if something came loose.

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I haven't actually tried that. The baffles are new and I think if they failed, they wouldn't create a blockage. I copied them from the 1929fordhotrod website http://1929fordhotrod.com/johnsblog...-exhaust-baffles-hot-rod-external-side-pipes/. My original baffles were cut from a glass pack (too small) and for the new ones I copied these with a larger diameter "tunnel" for less back pressure. Thanks for the suggestion.

 

One more thing off the list.

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If your right rear freeze plug is easy to get to , take it out and clean inside it with a coat hanger and flush . You will be surprised at all the crud that comes out . You will then clean the others .

 

Thank you for the suggestion. I may take a look at the right rear.....it is really the only one that is accessible (after removing the starter). The others are blocked by motor mounts and steering box, so I would need to pull the engine out. Right now, I am fighting with my block drains to get them out and get a peek at the same area.

 

Success!
After finding that my radiator was functioning okay (see thermal camera photo), I next flushed out the block as well as I could. I made an air/water flusher to try and also tried a toilet style power plunger that pushes water in and out (see photos).
My block drains had obviously not been out, probably ever, so I coaxed them by running the engine to warm up the block, then held dry ice (minus 325 degrees) on the plugs and worked them back and forth until they loosed up. This was after trying just penetrating oil and an air impact and destroying the hex heads. I bought a new tool (Maximum Impact Bolt and Nut Remover) that screwed down over the rounded-off heads and backed them out.
The opened drains did not drain until I cleared the holes with an awl. I flushed from the thermostat housing to each block drain, then to the water pump intake, using my squirt/suck flusher then the air/water flusher. I captured the debris so I could measure it when I was done. It totalled up to only about 2 ounces of rust particles ranging from the size of sand grains up to 1/4 x 1/4 x 1/8. They were all attracted to a magnet, I am guessing it was all rust and no sand. When I drained the rinse water after my test drive, more particles came out. If I add it all together with the rust I have already fished out or the radiator, It's probably 3-4 ounces total. I left the Tefba colant filter in, so I expect to continue catching particles for awhile.
On my test drive of about a half hour, the dash gauge got up to 180* and stayed there until I returned to my driveway, where it got up to 210* at idle before the electric fan kicked on, then it stayed there.
I am going to be satisfied with the results for now, but still install my new mechanical advance springs and other things that people have suggested. Thanks to all for the advice and usefull comments! View attachment 4180324 View attachment 4180324 View attachment 4180325

 

Congratulations on your success! Now for the fun part, worry-free driving enjoyment!!!

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Thanks!

 

As mentioned a few pages back I don't see a fan shroud. My problem was not as bad as yours but my engine creeped up with a shroud and the fan wasn't where it belonged. Finally placed it correct and no more heating. I also see a clutch fan. Things work different when using them.