ok here is the back story…

2 years ago we started having motor issues and after tear down it appears it over heated. Almost every ring had a crack, cam was wiped and had some bearings in the bottom end going bad. My engine builder felt like it may have been an over heating issue.

So now 2 years in the future…. the motor is back in as of about 4 days ago. I replaced the stock radiator with a new Dewitts, new lower hose and we re-used the upper hose (the hose we got from napa didn't work with the alternator belt. In the meantime we found a bad heater core and replaced that. We put at least 3 gallons of anti-freeze in before start up by filling through the top hose. We fllled the overflow tank to get the heater core filled and the lines to the water pump.

Started up and let run for a little bit to check for leaks….all seemed good and we decided to let it come up to temp. all good…so we took it for a ride, about 3 miles and i stopped at the local shop to set up an inspection. No problem when i shut it down, so we took off to head back to the garage. When i got to the garage and started backing in it started boiling over, but the gauge was barely to the 210 mark. It seems to puke out at least a gallon of antifreeze.

So now we filled it back up and took it for another ride, put about 10 miles on it and no issue until i got back to the garage again and shut it off, it puked again…it now seems to be a common occurrence, about 8 gallons of antifreeze and 2 gallons of water later. We put 110 miles on it this weekend and the temp only once went over 210, but every time we'd shut it off it would over flow. Driving home last night the temp went up to 210 and stayed there, even going down the interstate running between 65 - 70… we stopped at a gas station and noticed no antifreeze…so we added 2 gallons of water…yes 2 gallons! We added it through the top radiator hose until it came out the thermostat housing. We called my buddy to meet us with a trailer but decided to try going down the road farther..probably another 15 miles, and with water in the radiator the temp never got even close to 200..we got to the next gas station and pulled in to wait for my buddy with the trailer…the car puked again!



Im running the factory clutch fan, but no shroud. Im thinking about going to electric fans. I can't figure out how to "burp" this thing to see if its air bound. Oh and we made our own top hose now because the top hose that was on the car seems to have to much of a high spot in it.


so…i need some direction….im frustrated! This car has been owned by my father since 72, and we are friends with the original owner. Its not a 100% original car, I'm just trying to make it a nice driver.

 

If you are filling the radiator up to the cap, that's your problem. The early C3's did not have an overflow container nor an expansion tank system. The radiators had a mark on the side of the side tank (below the fill spout) which indicates where coolant should be filled. That leaves airspace for heat expansion of the coolant.

If you overfill it, the excess coolant just pukes out the overflow tube. But, when that cools down, the coolant level should be about right for the radiator/cooling system.

If you have an aftermarket radiator (without any fill mark), but no overflow or expansion tank, leave the [cold] coolant level about 3-4" below the fill neck. Or you can just let an over-filled radiator puke the excess out when hot. Then it will be OK, thereafter.

 

I have a Dewitts radiator, there is no fill on the radiator. I have an expansion tank on the passenger fender…. i figure the tank should take the excess and spew it out, but not every time i shut the car off.

 

sounds like a bad radiator cap to me, having air in the system would cause it to get hot and be low and antifreeze. We know electric fans without a shroud are about useless, i would think the same would be true of a clutch fan.

 

as in the cap on the over flow tank?

 

You have to get a fan shroud on there, no point in looking any further 'till you get one on.

 

If your C3 ran at 60 mph all the time with no tail wind you could get by without a fan shroud. But as your C3 spends most of it's time running at much lower speeds it absolutely needs a fan shroud to ensure the entire radiator is being used to cool your engine. So the fan shroud wasn't put on a radiator to protect fingers from the spinning fan as some folks actually think.

 

I have to agree with the others here, that the first thing you need to do is get a fan shroud on the car.

When you replaced the radiator, did you put all of the radiator seals back in place too. If not, buy a seal kit and install them. I learned years ago, when playing with road race cars, that you have to think of air like water. If it air meets any resistance, it's going to try to go around that resistance. Without the seals in place, air will go around the radiator, and not through it.

Does the car have the front spoiler in place? Corvettes are bottom breathers, and need the spoiler to direct air up through the valance panel, and into the radiator.

Are you running a thermostat, if not, I'd put one in. People seem to think removing the thermostat will improve cooling, but it often has the opposite effect.

Finally, you don't say what year you have, or what engine or trans. From your Forum name, I'm guessing it's a 69, and since you have an "overflow tank", I'm guessing it's a base motor, 4 speed, without air. If I'm correct, you have the 19" aluminum radiator, that does not have a radiator cap on it. If so, the tank you have is not an overflow tank, but instead is a surge or expansion tank, as the radiator does not have it's own tanks. I think the correct cap for your expansion tank is a 15lb AC model RC-26. It couldn't hurt to replace the cap, with the correct cap, or an equivalent one.

 

definitely get a fan shroud on there. when I was younger and stupid, I used to take them off and toss them. when I started working on jetski/seadoo type pWC's, I learned real quick about the relationship between the impeller and the housing. even a little too much gap and you drastically reduce thrust. same principle, different application...

 

It may be a number of things. First, the shroud does force the air to come through the radiator so it can do the job. And I am guessing you dont have a cap on the radiator, and use the surge tank for filling.
If you use coolant and can hold pressure to ~15 lbs. the coolant shouldn't boil until ~250 degrees - so check that the cap is good and you build pressure. With a new rad, I would put in a new thermostat. Then you know at what temp it should open. Run the engine to this temp, then let it circulate for a while and then fill the surge tank partially full - should be a mark. It could be that without the shroud the engine is running hotter than it should, and then when you turn it off, the coolant circulation stops. The engine is still hot, so the coolant left in the engine overheats and boils = puke.

 

I will toss in too retarded a spark advance or too lean will also make the engine run hot.
A lot of guys run 4* at idle "Because the book says so," which makes these engines run hotter and less efficient than need be.

 

thanks everyone.. and GB yes its a 69 350w 4spd. It has the stock clutch fan, motor is fresh rebuild and the water pump and thermostat were supposed to be new. Im going to get the shroud back on before i drive it again and change out the thermostat. Im also going to get a new cap. I do have the seals but wasn't thinking they were important and those are going on. So i do burp it for air at the pressure tank?

side note.. I don't know if it was totally base as it was a 350/350hp 380lbft car.. It doesn't have the stock intake, it has a snowflake intake and I just had to replace( in the parking lot of the show i just went to) the holley 750 for a holley street avenger 670. The 750 had the adjustment for the secondary float stripped out and it was dumping fuel.

 

I had that issue once. Bad cap

 

I don't believe the 350/350 had a burp tank or overflow tank. The overflow dumps directly to the ground. The radiator should only be filled to about 3" from the top. So if you have a radiator overflow tank it's not stock. If it is stock the radiator will blow out any excess coolant.

 

Some of the higher HP engines had a pressure (expansion) tank mounted to the inside right fender area. In that case, the pressure cap was on the expansion tank and a line ran from that tank to the radiator which did not have a pressure cap. The 'base' engine models had only a 'puke' hose, in case the system over-pressured (or was filled too much).

 

350/350hp has an expansion tank from the factory.

 

Yes and No.

I'm no expert.... but.... As I understand it, the L46 cars could be configured with one of two different cooling system configurations. First was the base system which consisted of an aluminum radiator with an aluminum expansion tank. The second is a 26" brass/copper radiator with no expansion tank. I own a 1970 L46 and it came with the second option listed.

Rick Bizzoco's 1969 Stingray Guidebook lists a number of original '69 L46 cars by VIN and their respective cooling system configurations. Judging from the list he compiled, there seems to be a huge running variation in how these cars were configured. Differences in the hood blanket (or lack thereof), radiator, core support-to-hood seals, etc. seem to have been phased in and out throughout 1969 production across many different engines as well as the L46.

 

A lot of different radiators were used in 1969 so it can easily get confusing.

Both Aluminum and copper radiators were used on L46 350HP engines. Aluminum radiators always used a separate expansion tank. Small block copper radiators were direct fill and had the expansion volume built into the radiator itself. This is why the fill line is several inches below the top.

Big blocks (except L88) used an indirect fill copper radiator. These did not have the built in expansion volume like the SB did and required a separate expansion tank.

John

 

I think whether the car had A/C (or not) also impacted which radiator was provided.

 

Yes, options helped determine the which radiator was used on a SB car. A/C and auto transmission cars always got a copper radiator regardless of engine choice. 1969 was unique in that both radiators types were used on non A/C L46 engine cars during the course of the model year. Auto transmission wasn't available on L46.

John