Overheats on the freeway but not when cruising around town?

[Kern Dog]

This car:

.....is a hodge podge of used parts, hence my nickname for the car, Jigsaw.
I put it together with a lot of parts that I had stashed away. I used a lot of used parts but bought new where it was needed. The 383 has been rebuilt, runs 9.3 compression with a 280-474 cam, Edelbrock RPM intake, Holley 750 Vacuum secondaries, 1 7/8" headers, 2 1/2" exhaust, the radiator is a Griffin aluminum 2 row that I used to have in THIS car:

Prior to today, Jigsaw only overheated once. That was due to being low on water. I simply didn't top off the radiator all the way after first fire. The cam and lifters were used and reinstalled in order so there was no cam break in needed.
I have driven the car maybe 150 miles since the engine install and all the driving has been local.
Today, on the way to a car show, my friend had it on the freeway and the temperature gauge was pegged. We pulled off to a gas station and let it cool down and added water. Once the needle on the gauge was to the left of center, we moseyed on to the venue. While idling in the line to park cars, it spiked again.
My experience with overheating is limited. I always place a high priority on using good radiators and stock belt driven fans.
This radiator worked fine in the red car and was only swapped because the A/C install I did required a radiator with a stock (1970) hose arrangement.

Common sense tells me that if the car runs hot while the radiator is getting enough air flow, it means that there is a coolant flow problem.
When I built this engine, I used a used thermostat, used water pump, pulleys, fan clutch and even the belt. I have only used straight water in the system though.
I'm going back to the venue tomorrow. I suspect that the thermostat is to blame. Maybe it is stuck closed. I'll know more once I dig in.
Anything else to look for? I'll replace the thermostat regardless. Some suggest to drill a hole in the thermostat to improve flow. What size hole?

 

[kiwigtx]

Are you running a solid fan, clutch fan, or electric fans?

 

[BeepBeepRR]

Seems like a bad fan clutch. Agree with Kiwi.. Air pockets in the cooling system?

 

[kiwigtx]

fan clutch

I see you said fan clutch now. At normal highway speeds? Seems odd to be heating up at speed, and not around town

 

[kiwigtx]

Seems like a bad fan clutch. Agree with Kiwi.. Air pockets in the cooling system?

Water might need 'burping'

 

[kiwigtx]

When the engine gets hot on the highway, have you tried turning the heater on Full to reduce the heat at all?

 

[Kern Dog]

Burping? I thought that I did that. I usually top off the radiator and squeeze the upper hose, let the bubbles burp out and continue to add water until it is just below the neck. This is a cross flow radiator.

The heater controls are really stiff and cranky to operate. I wasn't the one driving when it ran hot.

 

[kiwigtx]

Burping? I thought that I did that. I usually top off the radiator and squeeze the upper hose, let the bubbles burp out and continue to add water until it is just below the neck. This is a cross flow radiator.

View attachment 1456380

The heater controls are really stiff and cranky to operate. I wasn't the one driving when it ran hot.

I haven't seen a cross-flow like that before.

The water gets cooled by trickling down through the fine tubes.....that cross-flow will just allow the hot water to sit towards the top of the tanks on the side.

Is Ginger the same radiator - or is it a standard vertical fin flow?

 

[Orig69]

Do you have a spring inside of the lower rad hose?

 

[Kern Dog]

Generic Motors used cross flow radiators for many years. I bought that Griffin in 2000 when I did my first 440 swap in Ginger. It was a cheaper option compared to recoring my original 26" unit, though nowadays I wish that I had kept that one!
The Griffin never failed me when I had it in the red car, never. Ginger has over 100 more cubes too.
I just ordered a water pump and thermostat from a local parts house. I'll use real anti-freeze this time, I swear.
If the thermostat isn't faulty, I'll really be curious as to what else it could be. Freeway speeds should provide more than adequate air flow to keep and engine cool.
I have other fans and clutches here to use if need be. I may just roll out the arsenal of parts tomorrow and throw everything at it if the thermostat isn't dodgy looking.

I am not sure if I have a spring in the lower hose. It is a cut down OEM hose for something that I don't know. I simply picked through a bunch of hoses until I found one that looked like it would fit.
There were no leaks anywhere so I wasn't losing water outside.
The exhaust has no steam to it. The oil is clear.

 

[Kern Dog]

Is Ginger the same radiator - or is it a standard vertical fin flow?

Ginger has a standard style top and bottom tank, vertical flow unit from a trusted vendor, Speedcooling, ECP. I've driven in 110 degree heat and it never overheats. I do have a shroud on it though.

 

[4speed68rt]

Thermostat.

 

[1 Wild R/T]

My red car that I'd hoped to drive back from Texas overheated repeatedly... I tried radiators, water pumps, thermostats, knocking the freeze plugs out & flushing the block, a couple fan clutches & a solid fan... Then a two speed dual electric fan system.... It overheated through all those attempts.... Then I bumped the timing up... A lot.... And it finally got better... In the end I locked out all advance & set the timing at 34 degrees... I used a dead stop & verified TDC, the cam isn't big enough that it should even want full advance... It's a true measured 10.2 C/R it should ping, it doesn't... I don't understand it, I still question it but a friend who is really good at making big HP commented that some engines just aren't logical... But they will tell ya what they want..

 

[Chargerjase]

If you have never run antifreeze in the car, I suggest you do a flush. I did my car recently, used a proper radiator flush and ran the car for half an hour. Drained and flushed with water a further 8 times until it ran clear. Then flushed with distilled water a further 2 times. Drained the radiator and used concentrated mixture. I have a 383 and it took 16 quarts to fill the whole system with a 26 inch radiator. Might be a bit less for you if you have a smaller one. The block retained about 7 1/2 quarts after the radiator was drained. So to get a 50/50 mix, you need to work out the mixture, but it will be stronger than 50 percent obviously to allow for the distilled water in the block.
One more piece of advice, to burp the engine, raise the car a bit at the front end. The higher level will allow air to rise to the top and burp out. Or go to your local parts store and buy one of these funnels. They are brilliant and how I did mine. Good luck.
No-Spill Radiator Funnel Kit

 

[SlinktRR]

Run it with the radiator cap off from cold start until the thermostat opens. Trapped air in the block will get forced out, or burped out. It worked on my old all iron 383 when it overheated randomly out on the road.

 

[Kern Dog]

If you have never run antifreeze in the car, I suggest you do a flush. I did my car recently, used a proper radiator flush and ran the car for half an hour. Drained and flushed with water a further 8 times until it ran clear. Then flushed with distilled water a further 2 times. Drained the radiator and used concentrated mixture. I have a 383 and it took 16 quarts to fill the whole system with a 26 inch radiator. Might be a bit less for you if you have a smaller one. The block retained about 7 1/2 quarts after the radiator was drained. So to get a 50/50 mix, you need to work out the mixture, but it will be stronger than 50 percent obviously to allow for the distilled water in the block.
One more piece of advice, to burp the engine, raise the car a bit at the front end. The higher level will allow air to rise to the top and burp out. Or go to your local parts store and buy one of these funnels. They are brilliant and how I did mine. Good luck.
No-Spill Radiator Funnel Kit

That setup seems really weird. I've never used anything like this in almost 40 years of owning cars.


This is the first time in years that I've dealt with an overheating car where the symptoms were not immediately evident.
The following parts were used in another car that never overheated:
Radiator. Hoses. Fan. Pulley. Water outlet. Water pump.
I have the initial timing at 18-19 with the total at 34 degrees.
3.91 gears, 727 with a 2800 stall 11" converter.

 

[Chargerjase]

View attachment 1456429

That setup seems really weird. I've never used anything like this in almost 40 years of owning cars.


This is the first time in years that I've dealt with an overheating car where the symptoms were not immediately evident.
The following parts were used in another car that never overheated:
Radiator. Hoses. Fan. Pulley. Water outlet. Water pump.
I have the initial timing at 18-19 with the total at 34 degrees.
3.91 gears, 727 with a 2800 stall 11" converter.

Yep, I understand your concerns about the funnel, but it is an easy and innovative way to remove air from your cooling system. The overheating could be a number of things. If your timing is at 34 deg as suggested, it most likely has to be a partial blockage in your system or a failing component. If jigsaw has never overheated before except because of low coolant, then it can only be one of those things. You could flush the system using a radiator flush and water. You can do that cheaply and see if it makes a difference before you add antifreeze. Changing the thermostat is another quick and easy thing to do. By the way, you asked about drilling a weep hole in your thermostat earlier. This will allow the air to burp out without having to use the funnel. Picture shows about a 3/16" hole, but a 1/8" is perfect.

 

[Kern Dog]

I did still wonder about the hole in the thermostat. I've seen some with a small spring loaded sliding valve/pin.

For now, I'm going to swap some parts in the hopes that I can drive it back home on Sunday. I could just default to trailering it back home. That is a smack to the face for a guy that wrenches on his own cars though!

 

[493 Mike]

Yep, I understand your concerns about the funnel, but it is an easy and innovative way to remove air from your cooling system. The overheating could be a number of things. If your timing is at 34 deg as suggested, it most likely has to be a partial blockage in your system or a failing component. If jigsaw has never overheated before except because of low coolant, then it can only be one of those things. You could flush the system using a radiator flush and water. You can do that cheaply and see if it makes a difference before you add antifreeze. Changing the thermostat is another quick and easy thing to do. By the way, you asked about drilling a weep hole in your thermostat earlier. This will allow the air to burp out without having to use the funnel. Picture shows about a 3/16" hole, but a 1/8" is perfect.
View attachment 1456431

View attachment 1456430

 

[Geoff 2]

The 'hole' in the stat must be the most misunderstood item related to engine cooling. Production engines have a bypass in the cooling system. On the BB, it is the 5/8" hole in the water pump body, directly under the stat.
It has two functions:
- should the stat jam in the closed position, it bypasses the pressure so that the pressure build up does not blow out a welsh plug or hose
- allows for quicker engine warm up because some heated coolant gets fed into the inlet side of the pump.
Stewart Components started making Chebby race pumps in the 90s & had the bypass eliminated. The drilled stats were for use with THIS pump.
Many stats have a jiggle valve that will 'burp' the coolant. Some do not but there is always some leakage around it for air to escape & drilling a hole will do nothing for cooling, but will delay engine warm up, which increases engine wear & fuel use.

Many things can cause o'heating. At idle, check that the rad is not blocked with debris that has come out of the engine & blocked the tubes. A quick test, not always definitive, but simple to try:
remove rad from car. Block lower hose outlet with rag. Fill rad with water. Remove rag. It should drain quickly. If it takes awhile, rad is blocked.