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'68 350 SBC Running Hot?

6K views 57 replies 15 participants last post by  GlacierBlue68 
#1 ·
Hey all,

This may be me being OCD, and a lack of knowledge, but I was wondering if this is worth looking into.

I have noticed that at times, when in traffic on normal temp days (50-70* ambient), my temp gauge starts to rise past 180 up to 190-195. Because I'm in the city and do a lot city driving, I sit in traffic quite often. Now, as soon as I start moving again, the temp gauge drops back down to 180, but I know that if I didn't move and get air flowing the temp would continue to creep.

I know very little about what the PO did to this car, it was purchased less than a year ago from a local dealer, but here is what I know in terms of the cooling system:

- 3 core aluminum radiator (can't find a make/model, may be a cheap aftermarket part)
- 2 electric fans (1 larger 1 smaller, these are right up against the rad)
- New water pump
- Overflow coolant bottle and clear tubing
- There is no shroud on this setup

I have never seen the car get over 200*, but again I have also not let the car sit idling for more than a few minutes to find out. I don't want to start throwing parts at it if this isn't a problem, but wanted some advice if this is normal or not. I would think that once the engine hits operating temp, the stat opens, engine gets cold coolant and would maintain the same temp regardless of whether I am moving or not.

Thanks in advance.
 
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#2 ·
A shroud will most likely help. It acts as a funnel . The fans will then pull air through the radiator and across the engine. Others will most likely chime in .
 
#4 ·
It would be nice to know what temperature the T-stat is....a 195 "should" maintain 190-200 IF everything is in proper operating condition.

Things that can effect running temps….

*Timing
*Running lean
*Air bubble in system

(done any work lately ?)
 
#5 ·
I had it at the shop I bought it from in the fall, they had to put a new carb on it (edelbrock) and make a few other adjustments to the A/F mix. They adjusted the timing and the firing order, because the previous mechanic had messed things up pretty badly. However, this temp creep is not a new problem, it was like that day 1.

The radiator drain plug was leaking and I had to slide a new o-ring on it, but I'm not sure if that would've introduced air into the system, maybe?

Here is a shot of the current setup, like I said, I think this was a cheap route for cooling.

 
#25 ·
I'll concur with this, or something similar at least. The better the shroud acts as a funnel the better the air movement also, if that makes sense. Plus the linked one you'll notice flaps that allow air by the shroud at speed, which is nice.

The temps you are seeing is not a big deal, as long as the gauge is accurate. But creep at a stop is the fan not moving enough air through the radiator probably (the whole radiator).
I used a fan and shroud from a V8 Thunderbird from the 90's. It's a 2 speed fan actually and the shroud is shaped for air flow, and it works great. Keeps my far from stock motor cool in the heat we get around here (90's).
 
#7 ·
Is there a shroud I could potentially purchase to improve the airflow?

I was afraid that the current setup was near useless, just looks wrong.

As for the t-stat, is there a way to tell what temp it is set for? I want to say that the stock t-stat's for these cars was a 195, but I'm not 100% on that.
 
#8 ·
I would go back to the basics. Factory style clutch fan, and factory shroud. . You are not that far off from what it shy be running at.
 
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#9 ·
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I think he took off the original clutch fan because it ate up the shroud. I almost put this car through a wall the first week I owned it because the mounts were starting to go. If you made a left turn, and gunned the accelerator, the engine would physically move in the bay, probably an inch or so. It would in-turn pull the throttle linkage and the car would floor itself.

The mounts were original, and one of the first items that were replaced. I'll bet that since he never swapped them, the first time it happened it probably ate up his original parts too.
 
#11 ·
If you made a left turn, and gunned the accelerator, the engine would physically move in the bay, probably an inch or so. It would in-turn pull the throttle linkage and the car would floor itself.

That is exactly what happens when a original mount breaks. Most newer mounts are interlocked so even if the rubber tears it cannot raise like that.
 
#13 ·
#14 ·
First item on the bill is replace both engine isolators wit the newer style, aka, interlocking. You don't need a sudden WOT and run into somebody else.
Onto the temp, remember, the gauge is NOT calibrated, and only an indicator.
The thermostat controls the minimum temperature, the dissipation of heat method determines operating temp.
Other contributing factors for heat is the location of the gauge sensor - if in the manifold crossover along with thermostat, temp will be less than a sensor in the cylinder head, its closer to the heat source, the combustion chamber.

GM designed the gauge markings as the 10 o'clock mark, first mark left of center, is 180°; 12 o'clock mark, center mark, is 210°, 2 o'clock mark, first mark right of center, is 240°.
In the picture shown, I agree with others, poor set-up, one reason is I see a large potential for recirculating heated air about the rad/fan set-up. As the present fans pull air through radiator and exits, this heated air can, and probably does, get pulled through again through the radiator, until the Camaro moves forward giving cooler air. Remove the fans and go back to OE design of mechanical fan, minimum five blade, it can be a fluid fan, and a shroud. Good item seen is a smaller water pump pulley compared to crankshaft pulley, meaning coolant and fan will spin faster than crankshaft. But, remember, the faster the medium being pumped, whether the coolant or air, the less time for the transfer of heat.

Yes, thermostat can be checked for opening temp in a large pan of water, suspend the stat into water, and have a known good thermometer reading water temp.
Set stove on high and observe thermometer and thermostat. Stat opens at stamped temperature. Stat fully open at 10° above.

Assemble Camaro, and see what happens. An engine running 200° is not a problem. I have a '88 454 C3500 truck I bought new. It ran at 230° plus with a 195° stat. Three different dealers for the same problem - too hot.
First question from all three was "Is it puking?" "No, it is not." " This is normal."

So, if she runs a little warm, it's okay.
 
#15 ·
I'd dump the electric fans in favor of the stock system. It's proven to work very well.
The e-fans you have are not adequate and are poorly installed. The wiring visible in the picture posted is a mess and is likely to cause other problems.
 
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#16 ·
Everett, thank you for the thorough write-up, very informative stuff.

Unfortunately, I don't have a stock setup for the temp reading, what I do have is this:



I found where the temp gauge sender is hooked into the block and it is right by the t-stat. I also like the idea of going back to stock, doesn't seem like an impossible task either. Would the stock setup work with the existing rad or would I also need to replace the rad too with a stock one?
 
#17 ·
You should be able to go back to stock with what you have now.

OR

Get a proper E-fan like Vegas posted or a Mark VIII fan.

The set-up you have now IS your issue. You're only moving air in those 2 spots Vs. the whole radiator.
Think about it this way... you cooling system acts like it's the size of a dinner plate.
 
#18 ·
I love e-fans. They’ve been used on virtually every new car for the last 20-30 years.

Why? Because they work better than mechanical fans. At idle the mechanical is moving less air the at rpm. Well that’s backwards as you need more CFM from the fan idling in traffic than at speed. Electric moves 100% of the rated CFM at low and high rpm.
 
#19 ·
Thank you all for the advice on this.

FYI, this car doesn't have any performance mods, it's a bone stock (newer) 350 SBC from a different machine, and is actually geared at 3.11 to be more street/highway friendly. That said, going back to stock I feel would be a better move and probably cheaper too.

I am thinking that going with the following would work?

- Hayden 2747 clutch
- Hayden 3618 fan
- 23" fan shroud

This is what the current fan spot looks like:



Going back to stock would keep me under $200, a lot less than an e-fan setup alone. Would this work? Would I need a spacer or any other mounting hardware? Thank you again for all your knowledge, this forum is awesome.
 
#20 ·
There's a lot of good suggestions posted here. You don't have a big problem. You just need to pull more air in stop and go. Either get those fans off the radiator and into a shroud or get an OEM shroud and fan combination. Either will most likely solve your problem.
 
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#21 ·
Agreed, thank you for all the responses, I feel like this may also be a good option so that I can keep the existing fans. Seems like there are two schools of thought for fans, the electric vs stock clutch fan. Since the electric fans are there and working, I feel like I could make my own shroud for them, since they are two different sizes (don't know why).

https://www.northernfactory.com/Use...Applications of Engine Driven Fan Shrouds.pdf

All I have to figure out is how to mount it to the rad.
 
#22 ·
I feel like I could make my own shroud for them, since they are two different sizes (don't know why).
That is the patch of least resistance. I would recommend that the shroud is about 1 to 1.5" off the radiator core. An ac heating and cooling place could probably make one in a break. You'd just have to make your own holes.
 
#23 ·
Thank you, and I agree with Chris & John on the shroud and fans.
The shroud, as Chris suggests, can be made on a brake and would look similar to a shoebox top.
All you would need to do is attach shroud to support/radiator and cut holes for the present fans and attach them to the new shroud.
This way the fans would pull air through the radiator, sorta, rather than from the spots fans mounted now.
Keep the gauges you have, better info given than stock gauges.
 
#33 ·
no, 2.5" might even better if the fans are a good cfm. I am always concerned about you running out of space that's why I restricted it to 1.5"
 
#27 ·
as the picture in post #3 shows fans with a shroud. that combo. was bought as a kit from Champion for cooling 600 HP. at the time it dynode @ 532 and it would not cool the engine
within 7 miles the temperature went to 230
removed the E fans and went mechanical with a shroud and no problems since
you might consider a top and bottom filler panel which will force the air through the radiator
just a little more info. my friend had a 283 in a S-10 PU and it never did run cool with e fans . he worked at a salvage yard and had access to many fans
just sayen
 
#34 ·
Not disputing these numbers at all. We've had customers with very similar results. However, I want readers to know that we've also had the exact opposite happen in stop and go driving. ie; cars with mechanical fan and shroud running super hot at idle and running very cool once switching to dual electric fans.

Point is that everybody has different combinations and therefore different needs. Sometimes you just have to experiment to get the 'formula' right. :)
 
#28 ·
I'm going to try to fab a shroud around the current rad, and mount the fans to the backside of it as a start and see how that works. If it keeps me cool I'll consider it a success, but if the problem persists I'll got the stock route.

The fans are 12" and 7", and was planning to use both of them on the new shroud, I feel like this should keep me sufficiently cool while I'm at a stop. I plan to model the shroud after post #3 as well as I can, though I don't know if I will need vents since the fans will take up a good amount of the shroud as is.

Do I need to seal this thing around the radiator or is a small gap on the sides okay?
 
#29 ·
Though hard to tell I personally don't like the look of the shroud in #3, it looks too flat and too close to the core. It will probably be better at idle than what you have though. The one Vegas linked looks better, but again hard to tell in a picture.

Do both fans run simultaneously or are they separately controlled?

No need to seal it around the radiator.

Electric fan failures are because of improperly sized fans, or incorrectly functioning controls, it's not the fan's fault. OEM has been using them forever now, and they are over built typically for worst case scenario.
Stock fans work for sure, but so do wooden wheels and hand crank engines :wink2: . If you want a stock look by all means, but don't be afraid of electric fans.
 
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