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SBC Cooling Saga...can anyone offer a good suggestion I haven't tried yet?

9K views 91 replies 24 participants last post by  Houston54 
#1 ·
Hello, all!

I notice overheating is a hot topic (bad pun) here, but I wanted to dive in with my woes and see if anyone can figure out what I haven't yet. The history:

1968 Impala Custom, 275/327, TH400, dual exhaust with 'h' pipe. New suspension, engine still stock save for water pump and t'stat. Still gets 15 mpg +/= city, so she's still doing ok there.

BUT, she has a cooling problem from Aitch Eee Double Hockey Sticks I can't figure out or fix. For 2 years, the idiot light came on intermittently, but could find no trouble. Added an Auto Meter gauge with probe inserted in lower center of radiator, but this showed actual NUMBERS that freaked me out...well over 290 degrees, w/o the A/C on!

SO, I did the following, in order (rather, my Goodyear guy did it):
1. Back flushed the coolant;
2. Put in a (tested first) 180 deg. thermostat;
3. Added an Impala Bob's 4-core Desert Cooler radiator, along with auxiliary external coolers for the engine oil and trans fluid;
4. Put dual 16" electric fans on said radiator, mounted 1/8" from the core (no shroud of any kind was provided with the fans..they mount on dual rails that span the radiator left to right).

STILL had high temps as described! Now, I added:

5. 160 degree thermostat;
6. 40 GPM hi-flow water pump;
7. All new hoses inside and out;
8. New heater core (thanks to the water pump);
9. Went broke converting the A/C to the new refrigerant.

And still the problem persists. It takes the car just 15 mins or so to get up to 180 when the ambient temp is 85, but after that it just climbs to about 205-210. If I use the A/C, the temp gauge pegs out and coolant spews out the overflow!

As we all know, the cavernous interior of a '68 Full-Size Chevy takes awhile to cool, but I can't risk using it anymore. I'm fed up and broke, and the only thing I HAVEN'T replaced is the condenser, which seems fine.

What next?
What's the normal op temp for my engine anyway?
Do I need to replace the condenser with something new anyhow?
Should I try to make a shroud of my own out of rubber, etc, to cover the inboard areas of the radiator not covered by the fans?

Please help me...I hate to sound pathetic, but I can't deal with this any more, and need a positive fix!

Chuck
Norman, OK
 
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#3 ·
I'm betting your car came with a shroud, and you should have one on it. Your fan can't be effective in moving air THROUGH the radiator with out one. I agree, also, that you need to check your timing. If your engine is in good condition and good tune, and you install a fan shroud, you'll be in good shape.
 
#4 · (Edited)
Cooling woes...

Timing is spot-on as of 2 weeks ago, so I think I've managed to rule that out. As to the shroud, well, the one I have is for the original (shot) clutch-driven fan, so it won't accommodate the twin electrics.

The only thing I can think of is that the fans, though they are so close to the radiator, are mounted side-by-side w/o any gasket or shrouding...they didn't come with any. I've used metal tape to fashion a 'shroud' of sorts to cover the entire exposed radiator area around the fans and force all the air through the fans themselves. I'm sure I've missed a few small parts, but anything larger than 1/4" is taped over for now.

All I can do for now is see what happens, as I can't find any shrouding of any kind for the fans, unless I wanted to go to one big fan in the center of the radiator...

What bugs me is that the mechanics say that the setup I've got (with the fan size and the 160 thermostat) should have me running cool, if anything. @(%&^$*T&! We'll see...! No one can seem to tell me what the normal op temp for my engine/application should be, so I'm unsure of what to look for. I can only hope the 'shroud' I've fabricated will help...

Has anyone had luck in such a situation with replacing what looks like a perfectly good condenser?

Thanks for the heads-up, and I'll keep tabs on timing to see if things are going out of adjustment w/o my knowing. Again, any other ideas you have are welcome!

BTW, Busterwivell, my ol' girl is a former AZ car...lived in Phoenix until 2001, when I bought it.

Chuck
 
#7 ·
Going with the shroud thought...

Thx for the feedback! The radiator (even though a 4-core 'desert cooler') sits about 8" from the pulley. The fans are mounted side-by-side across the radiator from left to right, overlapping the sides of the radiator by about 1/2" on each side, and only project about 1 1/2" from the rear face of the radiator.I've tried to cover over this overlap, with marginal success.

The gap in between the fans (kind of like two triangles sitting point-to-point above and below the two fans) has been plugged with the 'shroud' made of the aforementioned speed tape layered over a thin piece of wood and secured above and below them. I intentionally made this to fit tightly between the fans, and nothing SHOULD get through this area now.

The 2" gap between the top of the fans and the expansion tank of the radiator has also been blocked by several layered strips of speed tape. I figure 90% of the air now has nowhere to go but through the fans themselves.

It just remains now to see if this works. If not, all I can think of is to change the two 15" fans for slightly smaller ones with an integral shroud and/or replace the A/C condenser and hope one or both work...everything else has been checked and replaced.

Chuck
 
#8 ·
The electric fans will do nicely without a shroud, as cmk59 described the install @item #4 of post #1.

I would pull the block drain plugs and verify that no gunk is left in the block from the flush. Many shops "flush" engines but really don't do anything meaningful. Assuming ignition and cam timing is right and the plug range is right, it should cool fine as long as the block is clear, meaning as long as enough water is actually able to flow enough to cool it.
 
#9 ·
Thanks, Bluesman!

bluesman2333 said:
The electric fans will do nicely without a shroud, as cmk59 described the install @item #4 of post #1.

I would pull the block drain plugs and verify that no gunk is left in the block from the flush. Many shops "flush" engines but really don't do anything meaningful. Assuming ignition and cam timing is right and the plug range is right, it should cool fine as long as the block is clear, meaning as long as enough water is actually able to flow enough to cool it.
I guess that's another chunk o' change I'll have to cough up. Can't physically do it myself anymore, but it's about the only thing I haven't thought of!

Thanks again, and I appreciate the help, even if it IS going to cost me...! :smash:

Chuck

Chuck
 
#10 · (Edited)
The only reason I even thought of it is that once I pulled apart a motor and was amazed at finding the cooling passages completely full of brown sludge. I guess it was originally from someone putting stop leak in it.

*Something else, make absolutely sure the cooling system holds pressure with a pump and gage. If it doesn't, it will never cool.
 
#13 · (Edited)
Shrouds and overheating...

Fan relay fuse blew ... think there's a short in the fuse holder ... the fans were pulling hot air out great guns, but temp was still at 220, regardless. I touched the fuse (literally) to the fan relay, and it blew. Geez......

Anyway, it's now off to the mechanic, and probably more of my stereo equipment off to the pawn shop to pay for it! ***grrrr*** And did I mention that it's not only our 7th wedding anniversary today, but the plastic radiator in her '88 Chevy truck blew yesterday? HOW MUCH FUN CAN ONE COUPLE HAVE, I TELL YOU??????? :D :welcome: :smash: :smash: :smash: :smash: :smash: :smash: :smash: :smash: :smash: :smash: :smash: :smash: :
 

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#15 ·
Radiator Cap...

Yep, radiator cap was replaced with a brand-new cap (16 psi) and checked before installation. Timing was literally right on the mark where it was supposed to be according to the Chilton's book (don't remember right now, but I remember being tickled that it didn't require any adjustment!). That having been said, I'm having my mechanic pick it up in the morning and re-re-check the timing AND ignition, as well as pop the freeze plugs and flush the block as was suggested earlier.

Am also strongly leaning toward the suggestion of removing the electric fans and putting a flex fan on with the OE shroud...maybe, just maybe leaving one of the electric fans on the condenser as a pusher, wired to the AC relay...

Chuck
 
#16 ·
cmk59 said:
Fan relay fuse blew ... think there's a short in the fuse holder ... the fans were pulling hot air out great guns, but temp was still at 220, regardless. I touched the fuse (literally) to the fan relay, and it blew. Geez......

Anyway, it's now off to the mechanic, and probably more of my stereo equipment off to the pawn shop to pay for it! ***grrrr*** And did I mention that it's not only our 7th wedding anniversary today, but the plastic radiator in her '88 Chevy truck blew yesterday? HOW MUCH FUN CAN ONE COUPLE HAVE, I TELL YOU??????? :D :welcome: :
Sorry to see you are going through this. Thanks for the pic's. Hey tomorrow will be a better day :thumbup: It can't get any worse!
 
#19 ·
The coolant IS getting hot, so the heat is actually being transferred to the coolant, but the coolant is not getting cooled by the radiator. If the block were sludged up, the heat would not be getting to the coolant.

Faster than 35 mph you should not need any fans at all (no AC on).
In any conditions, the engine should run no more than 10* above the rated thermostat temperature if the cooling system is working correctly.

At 290* you are obviously boiling all the coolant out of the engine and puking past any cap that actually holds 16 psi. 50/50 mixture boils at 256*.

Try turning on your heater full blast to see if it helps the cooling. It should make a difference.

Before a SBC begins overheating, steam pockets form inside the heads and continue to get larger until the heads are not cooling at all.

Since your fans are mounted 1/8 inch from the radiator, any shroud thing you have made on the back side of the radiator and between the fans is hindering cooling, not helping it. All you are doing is blocking the ram airflow through the radiator. Unless you move the fans 2 1/2" away from the radiator and then create a tight shroud to fit that gives 2" clearance for the air to move behind the radiator, you are not going to pull air all across the radiator.

IMO you should go back to the factory shroud and thermostatic 7 blade fan.
as a starting point. Be sure the fan is no deeper into the shroud than 1/3 the blade thickness.
 
#21 ·
Woe is me...heh, heh..

ScotF,

I honestly think I'm gonna do just what you suggested, but perhaps use a better fan than the factory type...something a bit more efficient that utilizes the same shroud. If that and draining the system completely (drain plugs, thanx, guys!) don't help as much as I think it should, one electric fan goes on front of the condenser, as I said before, just for grins to see if it helps.

Didn't consider the shroud hindering more than helping...hey, I know more about graphic design and audio equipment than thermodynamics! Well, the wife's truck goes in first to get her plastic radiator fixed, then my baby. She never has the problems I have, and that confuses me no end.

She has an '88 Silverado with a 305 and Q-Jet (basically the same setup as mine, with an electric carb), but with a little 2-core aluminum/plastic radiator, you can hang meat in her truck with the AC on and air temps hovering at 100F, and the temp gauge NEVER gets above 210. It just kills me!


Anyway, thanks again to all, and I'll keep you up to date.

Chuck
 
#22 ·
ScoTFrenzel said:
The coolant IS getting hot, so the heat is actually being transferred to the coolant, but the coolant is not getting cooled by the radiator. If the block were sludged up, the heat would not be getting to the coolant.
My experience dictates otherwise.

ScoTFrenzel said:
Try turning on your heater full blast to see if it helps the cooling. It should make a difference.
It won't though, too many BTU's to move.

ScoTFrenzel said:
Since your fans are mounted 1/8 inch from the radiator, any shroud thing you have made on the back side of the radiator and between the fans is hindering cooling, not helping it. All you are doing is blocking the ram airflow through the radiator. Unless you move the fans 2 1/2" away from the radiator and then create a tight shroud to fit that gives 2" clearance for the air to move behind the radiator, you are not going to pull air all across the radiator.
Electric fans do fine without shrouds and right against the rad. Go to a meet and look at all the cars with this setup. Not one overheats.

ScoTFrenzel said:
IMO you should go back to the factory shroud and thermostatic 7 blade fan.
as a starting point. Be sure the fan is no deeper into the shroud than 1/3 the blade thickness.
The reason for the electric fan in the first place was to try to cure the overheating condition. It didn't change anything. I still would like to see a pump and gage put on the cooling system, along with the cap, not that the cap is suspect. The idea is to look at things not looked at before because all the work to date hasn't changed anything. That's why I suggested the drain plugs and pressure test.
 
#23 ·
Those fans are too close to the rad, they are only pulling air over their diameter.
I went through the same problem, not until I made a decent shroud with space for the fans to pull from the whole rad did I get decent cooling.
This did´nt work.

This did´nt work.

This does.


 
#24 ·
I didn't mean to start an argument...

I think what we're arguing about here isn't whether or not something works, but a matter of efficiency. In most cases, the fully-shrouded fans will (yes) combine to draw air over the entire diameter of the radiator, and provide greater cooling. In theory, at least...no one I know of has ever done extensive testing to compare the two setups.

On the other hand, if you have no other cooling issues, the dual fans-right-on-the-radiator setup should (and often does) provide decent cooling...or at least, good enough to keep their users happy, else no one would be using that kind of setup.

I think both sides have a great deal of merit here, and I'm going to check with my mechanic to see if he can fab a shroud for my electrics. If not, I go with the mechanical fan again and put a single pusher fan in front...maybe.

Thanks LOTS to all youse guys for helping me identify other possible causes. I just wish I had a mechanic I could trade services with instead of cash right now...!

Take care,
Chuck
 
#25 ·
I don't think anyone is arguing at all. We talk back and forth about what we know and have experienced and we all walk away with more than we started with. I think your statement of "On the other hand, if you have no other cooling issues, the dual fans-right-on-the-radiator setup should (and often does) provide decent cooling...or at least, good enough to keep their users happy, else no one would be using that kind of setup." is prolly the best way to put it. All other things running with average or above average efficiency and this fan setup will be OK.

I have a huge interest in this because I'm going to do this soon. I like the look of electric fans without shroud so I'm hoping that my experience will be like most and not need one.

When the pressure test is done, it might turn up a bad head gasket which would be a cause of overheating due to the cooling system being unable to pressurize.
 
#26 · (Edited)
Boy, I sure hope you're wrong, Bluesman!

''I have a huge interest in this because I'm going to do this soon. I like the look of electric fans without shroud so I'm hoping that my experience will be like most and not need one.

When the pressure test is done, it might turn up a bad head gasket which would be a cause of overheating due to the cooling system being unable to pressurize.[/QUOTE]''

If you'll email me off-forum, it'll be easier to update you (cmk59@yahoo.com) I'm getting no indications of any kind that it's a leaky gasket or block condition, but on more in-depth testing, who knows?

Chuck
 
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