Technical Sbc overheating need help

I have a 1955 Chevy truck with a warmed over small block Chevy that up until now I've been running it without a thermostat and never had any overheating problems whatsoever but now that it's starting to get colder out and I drive it in the winter time I installed one, and now it will not stay below 240 on the highway and is going all the way up to 280 or more the gauge is pegged sometimes, going around town and sitting in traffic it never gets above 175, it can sit in traffic for over half an hour idling and never goes over 180, but as soon as I start going down the highway over 40 it starts climbing, oil looks good there's no oil in the antifreeze and no antifreeze in the oil, still has good oil pressure I just can't figure this out I've tried different thermostats but I'm stumped any help is appreciated

 

Check the thermostats on the stove in a pan of boiling water before you install them. Especially if you are getting them from an Auto Zone or somewhere similar. Went through four before I found a good one once and now buy them from NAPA but still check them. Never found a bad one from NAPA but re draining the coolant, removing the bolts and thermostat, cleaning it all over again then going back to get another one can end up costing some serious coin and time.

 

Nice looking truck, but perhaps some photos of the engine bay might help us.

There is no need for a fan to cool the radiator at 40 mph, there should be plenty of air passing through. So I suggest that perhaps the fan is not functioning properly and blocking air flow.

 

When faced with something like this, I always work my way backwards....what was the last thing I did
before the change happened? The only thing that is not constant, was the new thermostat. Start there
first and see what happens.

 

Make sure the lower hose isn't collapsing

 

Assuming you have things working right (thermostat is functional, hoses aren't collapsing, radiator isn't plugged, water pump is spinning the right direction) a radiator that can cool at low RPM but cannot cool at HIGH RPM is usually undersized for the task. It takes LESS radiator to cool at lower RPM because you are simply making LESS HP there. My truck was that way when I got it. Drive it all day long around town never a problem. As soon as you got on the highway itd slowly over heat. I put a bigger radiator in and it did the OPPOSITE. Why ? because now I wasn't getting the airflow I needed - added a shroud and now its happy around town or pulling a trailer on the highway. Something to think about as you look at everything.

 

Thermostat installed upside down?

 

280?

 

Sounds like not enough air flow through radiator at highway speed.
What is the setup for the fan?
Is there a shroud to allow fan to suck air from the entire radiator surface?
Is the radiator sealed to the inner fender panels and inside of hood with original sheet metal?
Is core of radiator clean or plugged with 60 years of dead bugs?
Hope this gives you some ideas for increasing airflow through radiator at highway speeds.

 

No heating problems what so ever until you put a thermostat in. Possibly the water pump is not moving enough and the added restriction is too much. Possibly the thermostat is bad or upside down.

 

What I have seen is guys will use the radiator that a friend of friend of a friend took out of there car, and it was good then? Than Y did they change it? I say You have a clogged radiator. It works good around town with no load on it. Put a load on it, No Good. Not enough flow at speed.

 

Does the truck have a heater? If no and there isn't a "burp hole" as I'll call on the thermostat you more than likely have an air block as mentioned already.

And as just mentioned check radiator for cold spots (run hand over "grill side" of radiator) which is an indicator of a plugged radiator.

 

I checked the radiator it feels warm all the way across as mentioned in a comment it seems to be flowing good it's the stock radiator but like I said in the summertime stuck in traffic for half an hour you never once did I ever have it go above 170, I've been daily driving the truck for about 3 months now and up until a week ago when I put a thermostat in it because it was getting cold outside is when I had the issue start because before I was never running a thermostat, the fan seems to be drawing in a lot of air but I do not have a shroud on it but as mentioned I didn't think the shroud would make a bunch of a difference at 75 mph which is usually what I'm cruising at on the highway, I have a hose going from the ports on the engine that would usually go to the heater core from one to the other just because I'm in the process of changing my heater core that started leaking so I would think it would be getting flow from that in place of the usual heater, I'm not sure if the lower hoses collapsing or not I do know whenever I pull over the system is definitely pressurized in the hose don't look like they're collapsing, I've heard of some people drilling a couple holes in the thermostat housing to allow for air bubbles and such to go through I'm thinking about maybe trying that along with another thermostat what's weird is the colder it gets outside the worse it's overheating which is weird to me, excuse the mess in the pictures it's a farm truck and there's just a little coolant from me working on it it has no leaks

 

A little more information on the motor, it's a small block Chevy 350 with 11 and 1/2 to 1 compression, the heads are 882 that are ported with stainless valves and Edelbrock valve springs, it has a 550 Lyft camshaft with 1.6 ratio roller rocker arms and retro fit roller lifters along with gear drive, the intake is a standard Edelbrock with an Edelbrock 750 on top, water pump was new when built it's just a stock one for a 79 Camaro and ignition is out of a '79 Camaro, for a fan I'm using a flex fan with an adapter and at full advance I'm running about 24° advance, I run 91 octane at the pump, and as far as if it's running rich or lean it probably runs just a tad bit rich but not much at all it runs like a dream, and the transmissions of turbo 350 TCI unit with a 2500 stall

 

I don't see a fan shroud or a coolant expansion tank?

 

11 1/2 to 1 farm truck? I like it !!!

 

My eyes arnt that good , but is that fan on backwards?

 

You need to block off the area around your radiator that allows the air to flow around and not through your radiator. Are you running your tranny fluid threw the radiator or through a separate cooler?

 

Harpo1313, I think your eyesight is fine! And logic correct it would appear also.

Chis

 

A thermostat, even full open, is a restriction in flow compared to no ‘stat. Maybe your setup is marginal without the ‘stat and even that small reduction in flow puts it over the top.

Drill two 1/8” holes in the ‘stat to allow any trapped air to pass as the engine warms up. Some come with this, and a little jiggler thing to break up any bubbles.

If it’s not new, change the radiator cap. Mine got “weak” with age and wasn’t holding the system to the correct pressure, leading to hot running and more overflow than the tank could hold.

Got a temp gun? Verify that your dash gauge is correct.



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Is there a spring in the bottom hose? Lippy

 

Temp gauge sender on intake manifold is not connected. Where is your gauge getting its info?

I also agree that radiator cap should be tested to see if it's holding at least 13 lbs pressure.

 

I'm gonna add a overflow and shroud this weekend I'm hoping that helps a little

Heck ya lol get a little squirrelly on the dirt roads sometimes though

The tranny cooler is mounted separate under the truck with a shroud

I'll check that today, I'm gonna pick up a new thermostat and drill a couple holes in it, what youre saying does make sense I didn't think of it that way, its very well could be possible that with the restriction of the thermostat by cooling system went from good enough to not good enough. The cap is new but new also doesn't mean it can't be bad so I'll pick up another

It's connected on the passenger side head I've always put them there and I've never had a problem before, would it be better to have it connected to the intake instead? Unplugged sending unit on the intake is just something to plug the hole




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What temp did it run without the thermostat? I ask because in my ‘57 the Stat stuck open the temp never got above about 145 on the highway.

 

On further thought I'm not sure a shroud will help at highway speed. It is a great help for those having problems waiting at the stop light.

At highway speed there 'should' be plenty of air flowing 'through' the radiator not around it. Question is why is cooling system not taking heat out of coolant on the highway?

Separate possibility:
Right side cylinder head temp sender; is it 'in' the coolant flow or recessed in an adapter that pulls the sensor back out of coolant flowing through the head? I've drilled and tapped the sensor end so I can make it longer using a brass screw to reach beyond the nipple adapter to the coolant flow.

Just a couple more thoughts.

Phil

 

So we've established the fan is on the correct way around, right? Could be ok, but doesn't look it.

Chris

 

If it only runs hot at highway speed it’s coolant flow period end of conversation. Sounds like the radiator is stopped up.


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The back side of the radiator looks a little sketchy, but I agree, it's probably partially plugged.

I had a nice stock 47 Ford. I had it for about 2 months and had driven it quite a bit around town. It needed a few things and I repaired each thing as it came to light. It never had a heating problem until I decided to go to a wedding about 100 miles away. I was running at 55 on the interstate and heard some pinging pulling a slight grade. I pulled over and found the car to be very hot. That's when I found the temperature gauge which moved, didn't indicate temperature. Re-filled the radiator after it cooled down and decided to press on. It started pinging about 5 miles down the road. Let it cool again and decided to head for home via back roads. It ran all the way home at 40 - 45 mph with no problems. Had the radiator re-cored when I got home. Never a heating problem after the re-core.

 

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I've seen a couple of hot rods where the temp sender was put in the passenger side head at the rear, that showed a more than comfortable overheat on the gauge. Moving the sending unit to the top of the intake made the gauge read normal temperature 195 - 200* range.

You've had good results doing this before, just food for thought.

 

If you're really only running 24° total timing , running that far retarded will cause it to overheat . 11 : 1 on pump gas with iron heads is a ticket to detonation!