Technical Chevy 327 overheating mystery

This is the original radiator, rebuilt and rodded out. That said, it was, no doubt, a custom made radiator to fit the space under the hood. I did check it with an IR thermometer and it was pretty uniformly 185* in all areas.

 

I like this as something to try before pulling the heads off. Also taking out the freeze plugs. Thanks!

 

I searched this online and found one. I can see how it would do a better job combining the air with the water. Thanks!

 

I hear you on this. If only I had suspected the rust problem before I started it for the first time, I would have installed my Tefba coolant filter first. As it is, rust particles sprayed into a nice clean radiator and some are too large to flow down through the cores, so they just sit there, probably blocking up some of the cores. I extracted many of them with a string of small magnets pushed into the filler neck, but I am sure there are some remaining.

 

You are right, there is no fan shroud, and no practical way to install one. Later Excaliburs had one and I entertained the idea of making a custom fiberglass one. The designers of my car used the shape of the hood panels to direct the airflow like a true shroud, but it is much less efficient. However.....prior to my rebuild/restoration there was never an overheating problem, even in the Arizona heat.

Originally the vacuum was connected to a ported source on the carb. I redirected it to the manifold and it did not seem to make a difference, so I put it back. As I read about that on the Internet, there seems to be a difference of opinion, so it is hard to know what is "right"

 

Does this car have a heater core plumbed into the cooling system? Is it possible that the heater core is mounted higher than the top of the radiator? This might might make it difficult to bleed all the air out of the cooling system.

 

Crap in the bottom of the block won't cause overheating [ I've seen engines with block filler grout in the lower half run safely on the street]
Crap in the radiator will cause overheating.

It is highly likely the cooling system was borderline when new! and now with more hp it will progressively get hot [more hp= more heat]

Pull off the bottom panel and try it.
Air doesn't***** up from the road, just the opposite.
There is a lot of turbulence under a car, but also a huge low pressure "vacuum" area. This is why pre "PCV valve" era cars ran a draft tube under the car.
And modern flat bottom racing cars now use this low pressure area for down force

Also look at making a shroud [from a "roasting tray"] and have the fan 2/3 in and 1/3 out to prevent air cavitation.

A fan shroud is only needed if Idling or low speed driving.
You could also make an aluminium "false firewall" type shroud that goes from one side of the engine bay to the other

The hot air still has to dissipate out of the engine bay

 

Yes, it does have a heater core, but it is more about mid height to the radiator. My method of getting all the air out has been to squeeze the top radiator hose until I get no more air bubbling out, then just keep filling the overflow tank after a run until the level remains constant.

 

When stored, did the inlet, outlet and filler neck get covered? I have seen mice do their thing here also. I wonder if a borescope could be a useful tool here? Digging the early Excalibur, pretty cool.

 

I appreciate your comments. I had a great plan to build a shroud from fiberglass, but I decided to add an electric pusher fan (2500 cfm) in front of the radiator and give that a try first. Especially after I learned of the designer's efforts to channel the ram air by putting a small panel (2 ft wide x 1 ft long) just aft of the radiator and just forward of the fan. So I have two fans now....the stock one and the electric. The electric one makes a big difference, and lowers the temp in traffic, but does not stop the overheating on the freeway. I have to keep remembering that the car ran fine in the Arizona heat before my rebuild/restoration, and without the electric fan or coolant overflow tank, or a shroud. The engine was rebuilt as stock. I still have the shroud in mind, but want to make sure that I am not fighting any rust or other blockages.

I am curious about your comment about block filler grout. I will learn more as I go along, but I thought I was trying to chase down a blockage in one or more fairly narrow coolant passages, as opposed to a larger void with coolant surrounding the cylinders.

 

The inlet and outlet were stuffed with rags and the radiator was put into a cabinet with doors, so it is not likely that anything got to it. I did look inside with a bore scope when I was fishing out rust particles in the top tank with magnets. I am pretty sure there are some particles left in there, but I ran the exhaust of at shop vac into the radiator and the outflow was pretty strong, so it is "mostly" clear.

Thanks for the compliment on my car...….she is a joy.

 

Have you pulled the plugs to see if #5 is running lean? Could a yellow jacket or something else left a restriction to intake flow to #5? When you used the pyrometer was it just running the engine in the shop or after the car was up into the upper ranges of over heating?

 

That is a good thought. I have pulled the plugs a few times and seen no remarkable differences between any of them. I will pull them again and take a look. I wondered as well about possibly a lean condition at #5 due to a vacuum leak, but I was unable to detect a vacuum leak with a propane bottle. To check restriction to intake at #5, I guess I could take the carb off and see if I can stick my borescope in the direction of #5. The last time I used the pyrometer, when I found #5 hotter than the rest, the car was idling in the driveway and had gotten up to about 170* on the gauge...….still not fully up to temperature. You give me the thought that I should repeat the test and get right on the #5 area when it is cold and see how quickly it warms up compared to the other cylinders

I am making a list of all the things I am going to try...…...Thanks

 

That's not an indication f overheating, it is a normal function, that is the purpose of the catch tank. But, 245* is too hot anyway. Question, what is the temperature differential between the radiator inlet and outlet?

 

I had an overheating problem when I had an electric fan in running all the time front of the radiator along with the mechanical fan at highway speed. The electric fan helped when I was stuck in traffic but I removed it and only use the mechanical fan now. My thought was that the electric fan was disturbing the air and blocking the air flow at highway speeds.

 

That is a good question. I am going to check it and report back.

 

That could be an issue for me as well. It is a big fan and covers almost the whole radiator. The grill that the radiator mounts in is somewhat restricted as well...…..1/4" square holes at 3/8" centers, so 67% perforated. So I think the fan "overpowers" the restriction in the grill, at least when I am in traffic. The grill is kind of a signature feature of the car, so modifying it will be a last choice option. I will be happy to remove that fan when I can find the cause of this overheating and fix it!

 

You should see about a 10* difference between them if the radiator is doing it's job.

 

I would be curious about the under hood temps in your car!

Firstly the designers didn't put ram air system for the radiator . An air dam in front of the radiator would be more efficient [diverting incoming air into the radiator]

I was once shown a test by an old race car guy , where he used a tuft of wool to show the flow of air
In his case the fan was just recirculating hot air around the engine bay when idling. ["forwards at the sides, and rearward in the centre at the fan"]

The idea of a shroud is to get the fan to pull air from all 4 corners of the radiator at slower air speeds than the fan
Even electric fans on modern cars have shrouds.

And I will be fitting a shroud to my 57 Chevy [a car notorious for getting hot in traffic]

If the car ran fine before the rebuild.......then what has changed.
Is the cam retarded ? Ignition retarded? Compression raised? More hp?

You need to stand beside a car that is hot and idling and feel the heat coming out from underneath. then do the same with your car with it's bellypan.


I've seen many [race] cars with healthy cooling systems and mysterious overheating issues that were cured by using 1" spacers under the rear hood hinges [a practice now banned for fire safety reasons]

 

I remember when the '68 Vettes came out the had an overheating problem. The cure was an air dam a little over one inch deep across the bottom of the air inlet for the radiator.

 

Has the timing cover pointer or dampener been changed? Might want to check true T.D.C. with a piston stop and degree wheel,. All in at 2350 r.p.m. should be good but I always check it at 3000 and 4000 to make sure its peaked.

 

After reading thru the thread, your overheating is a highway speeds-primarily? I think that pusher fan is an issue, blocking flow. Agree with all statements on radiator shroud is needed.

Got nothing on #5 running hotter than has already been discussed, interested to see the outcome on it.

 

I'm thinking about 2 things:
1. Pusher fan blocking airflow at speed....you said you installed at the rebuild and didn't have it before
2. Underhood temps....one of the signature features is the way the exhaust is run. That is a lot of surface to give off heat in a confined space. I know it didn't do it before the build, but you changed some of the engine specs "made it hotter" so to speak

Edit: I looked at the engine pic again and saw the heat insulation wrap on the pipes under the hood. Probably not that issue then

 

I have run into this before are you sure your pusher fan is pushing if you swap the leeds on a DC motor it will run in the opposite direction.

 

If it’s running hot on the highway it is not a fan or shroud issue....don’t need either at speed. The electric fan could be blocking airflow. The key here is it didn’t run hot before the rebuild so no need to redesign the car. Need to look at what’s changed since then. It doesn’t sound like it’s enough of a horsepower increase to make a difference so tune? Start simple.


Sent from my iPhone using H.A.M.B.

 

I noticed in your engine pic that you have a clutch-type fan. Is it operating correctly?

Sent from my SM-G892A using The H.A.M.B. mobile app

 

I will check the under hood temperature. I know there is a lot of hot air blowing back over the engine when I have a side of the hood open, but I have never measured it. With the hood closed, there is a lot of hot air coming out the
top and side louvers cut into the hood panels.

The only new (or different) parts used in the rebuild were a heavy duty oil pump, chrome moly rings, hardened valve seats . No changes to the cam, compression or carburation. Other than that, it has a known rust problem and (I imagine) the engine has some extra friction. I tried to measure the friction with a torque wrench at the crank bolt and got about 20 ft/lbs. The engine has abut 1000 miles on it now. The rust problem is more than surface rust, as there are many little chunks, about the size of a #6 flat washer that I have flushed out.

 

I did verify TDC with a piston stop and it is off by 1-2 degrees (retarded). Also, I checked the advance at 2500 rpm and higher and it remained the same.
Thanks

 

The overheating is really at all speeds, but it really struck me once when I floored it on the freeway and the temp went rapidly from 180 up to 220, after being steady at 180 for awhile. I suspected a "shower" of rust particles coming out of the block and landing on the top of the radiator cores and blocking the coolant flow.

Last evening I measured the (external) temperature rise of cylinders 3, 5, &7 while idling in the driveway, with a IR thermometer pointed at flat spots on the head just aft of the spark plugs. They went up together for the first 4 minutes from 52* to about 140, then at 8 minutes, #3 was almost 200, #5 was 250 and #7 was 175. At that point the temp rise leveled off and #3 ended at 225, #5 ended at 265 and #7 ended at 200. At the end, my dash gauge was 220*.

 

I installed the pusher fan, but only after the overheating problem became evident and early attempts to correct it with flushing, etc were not fruitful. The exhaust wrap on the manifold was not on the original, so it is a new feature of the rebuild.
Thanks