Technical SBC 350 Getting Hot on Highway

Probably the smart thing to do.

 

How would that be possible ? The coolant return on the SBC, is the upper rad hose.
The water pump pushes the coolant into the motor. How could it bypass ?

 

Anyone using an afr gauge will notice that the readings are not good data until these temps.

 

Also, looking at the pic in post #117, I'm wondering if there is a seal between the top of the radiator bulkhead and the hood?

 

Not on a 61 Impala. There are tons of places for air to bypass the radiator if the path through the radiator is too difficult to push air through.

 

Correct.

 

BINGO!

 

If there is too much coolant entering the bypass, then it is not going through the thermostat for the normal cooling path. When the thermostat opens, the bypass should flow less, but too much bypass helps keep the thermostat from opening all the way, but if a thermostat is a higher temp one, it may not open all the way and coolant is entering the bypass and you get a false reading. (I think)



Whoops..........some duplicate pics.

 

Has anyone ever seen an external bypass on a SBC ? I haven't.

 

None of my 4 have it.

 

I think the idea is that just because you can make coolant not boil until it reaches a higher temperature......does not mean that its a good thing to run your engine at these higher temperatures. A lot more engines seize up when running too hot than when running too cool. You also have to consider what these elevated temps do to combustion chamber temps ......possibly contributing to/causing detonation.


Quote below is not by me.

"Heat is the primary cause of detonation, and frequently one of the underlying causes is a cooling system that is not up to the job. If your engine's output has recently been increased but your radiator is still stock, it may be time for an upgrade in that area. Short of replacing the radiator, a better fan, a more effective fan shroud, or a coolant wetting agent may have enough of an effect to reduce or eliminate detonation. The explanation of the cooling system diagnosis is beyond the scope of this story, but we'll leave you with one big tip: Sweat the small stuff first. In the race to build performance, it is often the little thing like shroud sealing, thermostat operation, fan clutch engagement, or water pump cavitation that lead to detonation."

If its racing and performance for short duration is the all out goal, then higher temps may help......but even at the drags you see people artificially cooling their engines between rounds. It may not be best practice, but I always like the 180-190 range because I have a good broad cushion before it gets too hot.

 

Fuelie Corvettes have a external bypass hose.

Gary

 

I didn't say "external", but here is a video that will show you a smallblock Chevy with an external bypass. It affects which intake manifold and water pump you need to use. Listen very carefully at the 4 min 07 sec mark....and again at 4 min 25 sec.

www.bing.com/videos/riverview/relatedvideo?q=coolant+bypass+smallblock+Chevy&mid=471F23F6CD8E5C0A5174471F23F6CD8E5C0A5174&FORM=VIRE

On the next video you don't need to watch the whole video, but listen to the problems the guy had during the first 2 minutes caused by trying to get the bypass right.

www.bing.com/videos/riverview/relatedvideo?q=coolant%20bypass%20smallblock%20Chevy&mid=ED4CB8A57564B21FE624ED4CB8A57564B21FE624&ajaxhist=0

Many people switch pulleys and brackets and swap Vortec heads. They may not be aware that they need to address this.

 

If you’re concerned about all or most of the air flowing thru the radiator, in 1955-56 Fords used a metal shield mounted on the radiator support with a rubber seal to the hood. It was missing from mine and I found one. It defiantly helped with the cooling and ma help with your problem also.

 

Got it, thanks.

 

I've seen these filler panels (also pictured below) for various X-frame chevies but haven't used them. Regardless, I think the fan shroud design is causing a lot of his issue.

 

Ditch the electric fans and shroud and go with a 6 blade factory style engine driven fan, also increase the radiator size height, width, and thickness the more cores in the radiator the better 2, 3, rows is not enough, you need 4, to 6 core rows.. lastly use a seperate trans cooler that's not part of the radiator and not mounted on the radiator, put ot below or to the side out of radiator air flow.. What you have now will never run cool.

 

Just as you need to make sure that your water pump is turning the correct direction, there are electric fans that pull and electric fans that push- make sure yours is blowing the right direction

 

Nope. A bunch of that is antiquated.

1. Aluminum rads usually have 2 cores of 1" or larger tubes. The old "have to have 3 or 4 cores) is copper-brass, not aluminum. Aluminum rads can flow better as a result.
2. It's about air through the rad, it doesn't matter to the air or rad whether the fan is mechanical or electric. That's chasing money spent with more money spent for no reason.
3. The cooling system IS keeping the car cool, just not at highway speeds. It's keeping it cool in stop and go, so it is working.

As was discussed previously in the thread, his shroud appears to be the most likely issue. Taking it and the fans off and going for a drive will tell whether he has an issue with shroud design. With the design of the cheaper rad and fan setup he bought, I'm betting modifications to the shroud would solve his issue without the hundreds of dollars spent you're suggesting.

 

I,ve learned through the years that shrouds on a radiater to prevent heating is almost a must I,m confused... Gene

 

Those electric fans Just don't do the job and you have to keep spare ones in the trunk for when they fail. I did the changes I suggested to my 350 Chevy in my 38/40 Ford and it fixed the overheating. to each his own, just offering some help. I forgot to mention, put a large area washer with a 1/2 in hole in it instead of a thermostat, one less thing to break.

 

I hope the OP comes back to this thread and tells what he/she has done for the fix. This thread has been oddly enjoyable the past few days.

 

Crap yea. Fixing problems that almost don’t exist is fun

 

Some checking shows that the part number he posted for the pump is for a clockwise pump and even with the flat belts he is running the pump in a clock wise rotation.

I'm not seeing much of any way for air to bypass the radiator though holes in the core support that shouldn't be there or gaps between the radiator and the support.

Timing = been there done that with late timing. I don't even know how the 350R in my 51 Merc ran with the timing that late but It ran down the road at 80 pulling a trailer for hours on end.

Looking at some 61 Chebby under the hood photos there isn't much space for a lot of air to get between the core support and the hood. I've seen 49/51 Merc guys leave that panel over the radiator off all too many cars because "it blocks the view of the engine and I don't like that" and have similar issues. Air going over rather than through the radiator.

That comes down to lower hose collapsing at speed or that cute fan and shroud setup blocking too much air at speed.

 

Removing the thermostat decreases operational efficiency, and reduces BOTH power and milage.

 

A decent one does. Those shrouds are so close to the rad and cover so much of it up once you’re doing more than 30mph they become a hindrance to airflow.

 

Exactly why the OEM stuff doesn't look like that.

You can make it work well, OR make it easy/cheap to make.

 

I read threw all,
I will waste some time,
I think , (like others have said )) main problem is Not enough airflow at highway speeds going through the radiator,/core..
Air is stacking up &'leaking in front of radiator bleeding off in front of core support and other places not flowing through the radiator cores @ Hyw / road speeds , because of fan shroud
That fan shroud is a poor design , needs to be modified , but best to remove an ad
70'-80s shroud , cutch fan best but not required,

Timing Forget about Vac Advance for now!! until you get your cooling under control,
12 -18 initial btc
Total 34-38

also when it comes to coolant temps,
I have done !!!
Get yourself four temperature gauges ,test and calibrate them in warm 200 degs of water, Write down the difference between the gauges if there is.. stick them in four different places on a small block Chevy and you will get four different readings of coolant temps

 

there's a large group of people that come here... soon as they get what they want they leave no matter what...but at the same time there's a bigger group that comes here looking for info that don't post at all...not say'n that the group here is bad,. but some don't take the constant ribbing that goes on so they just keep quiet...kinda the red nose reindeer deal, but all in , they a lot of good things post here that are helpful for one trying to fix stuff their self... so it works IMO... that and the entertainment of the discussion pretty hard to fix someone's car on the internet, or over the phone,... and with out feedback from the OP as to what worked it doesn't have the value that would be there with it...I had a problem with my model A getting to 240 and climbing, so I fixed it...I now have a new problem,. I fixed it so good that now It won't warm up... at 118 out it now runs 170-180.. not hot enough...I want a maintained 200... at 180 the the 383 stroker doesn't perform well... I did every thing but the stat, and my guess is it's a 165.. no elect fan, or shroud, so my next fix.. a 180 stat




I also wanna add, the first thing I always do is the towel test, I hold a towel in front of the grille, if the fan doesn't suck the towel into the rad and hold it.... I start there... also, on this one I did the zips riser... works awesome

 

The idea of a stat is to keep a constant engine temperature.. when the engine warms it starts to open and allow cooler coolant into the engine,,, then starts closing as the temp drops.. when this happens it allows the coolant to cool in the rad...all the while keeping the engine at a constant desired temp... too cold of a stat will cause the stat to open too soon and could also cause an over heat problem because the coolant goes through the rad. too quickly, so you end up loosing the rad. efficacy and end up will an engine with a lot of coolant all the same temp///