Technical SBC 350 Getting Hot on Highway

A local friend of mine floated the idea of the ported vacuum as opposed to the manifold vacuum but we didn't get to the timing adjustment. He may have assumed I knew what I was doing which is apparently wrong.

So would you just focus on the 34 at RPM or try to set the initial at a certain number as well before reconnecting the advance?

 

As squirrel suggested above, with the vacuum advance disconnected and plugged, Rev the engine to 3000 or 3500 and see what the initial and mechanical (total) advance show. Move distributor to get this total advance to 34 degrees.
Then reconnect vacuum advance. Adjust idle speed.
Go for a drive. Listen for pinging, which will probably not be an issue.
Report back on temp gauge at steady highway cruise.

 

Didn’t say it’s wrong as you can tell by others replies. I said “typically” connected to ported/timed port. Which is a the case when engines a pretty much stock.

 

Sorry that wasn't directed at your response but more a dig at myself.

 

No biggy.

 

read the plug strap and see if you 're getting enough advance....thats the only thing that matters....setting advace gets a base line.... I start with a snap-on back to zero so I can see total advane..... 50 degrees?.... my starter wouldn't even crank the motor over..... never heard of running 50 degrees total.... must be a hamb thing....

 

SBC's normally run 32-34 degrees total Mechanical advance. Should be "all-in" by about 2,500-3,000 RPM's.

initial timing SBC | The H.A.M.B. (jalopyjournal.com)

 

Upper? Is your set up reverse flow?

 

As plenty have stated, I would bet on the timing being the cause.

My old late 80s C10 was bone stock and had a timing retard module. It started going bad and would pull timing randomly. Truck would lose power and start to run hot at cruise but was ok coasting or idling.

In that truck I ran 14 degrees initial with vacuum unhooked. 16 degrees it dieseled so 14 was it's happy spot.

another car I fixed had a stout sbf in it. High compression, big roller cam, etc. They set initial around 4 degrees to run pump gas but the car had terrible drivability and overheating issues. Set that one to 14 and the car loved it. No mor stumbles, surges, loading up, overheating

I usually run more initial timing than recommended but the cars seem to like it. My other car had a 9.5:1 350 with a mild cam and vortec heads. Initial was 13 on that one and ran great. I started at 6 and the car ran hot and stumbled. Kept moving it up until it pinged or dieseled then backed off 2 degrees and it was good.

 

A mechanical fan with a simple hoop shrould would allow more flow at highway speeds and should work fine at low speeds.

Gary

 

As soon as I read the thread title, I knew someone would bring up the old "coolant moving too fast" myth.

Do you have a coolant recovery tank set up, or just a radiator with a cap? If the latter, it's not uncommon to see a hose collapse a bit when the engine cools off. In those systems there is always some air in the top tank to allow for expansion of the coolant as it heats up. Your coolant volume "shrinks" as it cools off, creating a slight vacuum in the system which can make a hose collapse. Once the engine runs and heats the coolant the hose will return to it's normal shape.

 

Yes, I would focus on "total mechanical timing" at higher RPM. But after setting total, I would note what the timing is at idle, and also see when it starts coming in.

Let us know what happens

 

I betting this fan set up is the problem...might work good at slow speed, but blocking all the air flow at highway speed... take all that stuff off and put a good clutch fan on the motor

 

why did you change the radiator? and what fan did it have before?? do you have to add coolent????

 

also,,,, try this.... leave it as is.... run down the freeway, turn the heat on max fan and speed... temp should come down on the gauge.. this also will help remove any air in the system, and will tell you if the rad. is the problem

 

With the vacuum disconnected and plugged set the initial at 8-10* and rev the engine to 3000 rpm or so. Check your total and if your distributor is stock I expect you will see something in the high 20’s or low 30’s. Sometimes the factory advance springs are so strong it holds the total back. Now hook up the vacuum canister, and BTW I prefer manifold (full time) vacuum. Take it out for a test drive and see if you hear any detonation, or some call it spark rattle.
Putting your foot in the throttle will lower the vacuum reducing your total, but you may hear some rattle. If you do take the initial down a degree or two and see if that helps. If you had 34* total with vacuum plugged and say 12* vacuum (some vacuum cans give even more than that) it will instantly drop when you floor it. Vacuum advance helps mileage and lets the engine run cooler and has the added advantage of taking away that extra advance when you floor it. I’d try it, it only costs a bit of your time.

 

My 350 never drops below 200.
don’t need it to
Lives aroumd 215
No issues
Never overheated

 

200* on an SBC should be fine. No problem here to fix.

 

Go ahead and install the flaps. Minimum effort, maximum return.
You can use a silicone baking sheet for the flaps.. get one as thin as possible or flexible as possible..

Scroll down from here..
https://www.49fordcoupe.com/Under-the-hood-modifications/i-x7BwtfP

 

First thing is to verify that that gauge is actually reading correctly. Do not frigging assume that it reads correctly.
If it doesn't have a spring inside, that lower hose may be collapsing at speed when the fancy pump is pulling coolant through it with more suction than the system can handle. At idle or low speeds it isn't trying to move coolant at an excessive speed.
One thing I have done with a number of rigs that I was going to road trip in or tow with over the past 50 years is take an old thermostat that is set at the temp I want and remove the guts and just run the washer part. That usually gives enough restriction to maintain temp but there is no chance of it acting up.

The one running hot issue I had on a trip was due to the distributor timing being retarded rather than advanced. We got in a big ass hurry and "set it by ear and it sounded great and we hit the road with it and were fighting heat issues. We didn't get it fixed until I stopped at some guys shop in peanut country in west Texas and he helped me set the timing and then I was back on my way to Bonneville.

 

There's no such thing as a "2 core" radiator !
I believe you mean a 2 "row" radiator.

And there's no reason that a normally built, properly tuned small Chevy should run much over 180°. I've had MANY small block Chevrolets in my driving years (73 yrs old), and have never had a problem with over heating when there was no "underlying" problem.

Hell, I even have a 493 inch Chrysler, with 10.98 compression, that runs right at 170° with a 160° thermostat on...the street !

Mike

 

Ummmmm.....

 

220F isn't too hot, as long as it never boils over.
All the late model junk runs that hot all day.

Anyone think a normal water pump would help here ?

 

Your two 11" fans actually cover less radiator surface than the old single 16" (190 sq in on the two 11", 201 sq in on the single 16"), so you lost a little there. Taking into account the area taken up by two fan motors vs. one, you've probably lost more.
As was pointed out above, add the flaps and get more air movement going down the road (when you're producing more horsepower & heat).
Address any timing issues.
Good luck!

 

a 2 row rad. is the same as a 2 "CORE" rad. I notice the huge amount of free advise here.... you get what you pay for... I fight this daily at my shop..." a guy on the internet said this" and all so." I've been to 10 different shops and my car still over heats... I own an auto AC repair shop in vegas.... when it's 120 degrees out the phone rings off the hook.. and not to sound like an A hole... but the first thing I tell people is I'm not gonna fix your car over the phone... bring it down and I will tell you what is wrong... I have thousands of dollars of equipment... I can put my fan speed meter in front of the grille and tell you in seconds that that fancy china 2 little fan set up with a shroud blocking 50% percent of the freeway air flow is gonna cause it to run hot, a proper tuned motor doesn't need a fan to run down the hiway.... thats why they have clutch fans..... when you hear them roar is because they are pulling more air than 60 mph.. an elect fan that has too low of cfm will block air flow. and when the motor cools back down they shut off... and there is no myth...if the coolent runs through the rad tooo fast, it will run hotter... but there you go,.. I'm an expert at auto AC and coolent problems.... and have been fixing hot rod cooling problems for 50 yrs.... and the ones I fix don't come back unless something fails.... not to redo it... some of the things people post are just fish'n for likes and to get some thing going.... if you know what you are doing you know period....it's kinda like say'n I wanna bake a chocolate cake, what do I need.???? and some one says.... I always put a big can of chili beans.... those that know thats wrong usually don't say much because it just feeds the troll... listen to what I say and your car will run cool...

 

very good advise, only thing I would do for a fast fix is just get rid of the shroud and mount the fans direct to the rad.... that way it would eliminate the freeway speed blockage,,, and also address the thermoset to get to the correct temp... that way "THE COOLENT " doesnt go through the rad too fast and has a chance to cool

 

I do, I think, or know that combined with the big tube 2 core row rad... the coolent is going through the rad tooo fast...

 

flaps are band aids to fix a poor designed fan shroud'... they fixed one problem and cause two new ones

 

also,... one more thing,... lol...there is no reason that a 61 chevy with that big of a rad, surface should have any problems cooling, or having ice cold AC..... at 120 ambient temp my 53 chevy with probley the same motor runs at a constant temp and will freeze you out

 

the reason you disconnect the vacume is all you are after is base timing... and using a basic timing light... when I do it i'm not concerned with base.... I wanna know where I'm at all in so I use a back to zero light... stock timing pointers show zero timing, pus a few degrees.... most don't have a full degree wheel balancer... so you run the motor up till the dist. quits advancing.... turn it to 32 degrees... then tune from there...some times starters don't like more than 32 degrees, and thats because of the advance curve ..... but if every thing is stock thats usually not a issue.... when you are leaning on the motor to squeeze a couple ponys more... it can be found in a couple degrees all in...but thats 1/4 mile stuff...