Hello, I am asking for input on what I think may be an issue with the cooling system in my new-to-me 1969 coupe. This will be long but I am trying to give detailed information so someone may be able to point me in the right direction.

First some details about the car. It is a 1969 L46 4-spd without A/C. Original block/heads, but mostly aftermarket parts beyond that. Aluminum radiator, electric fan, plastic coolant reservoir, Edelbrock intake, and Holley 4-bbl carb. Did not receive much in the way of documentation/receipts when I purchased.

For background, I am good at following instructions and feel comfortable doing most work, but have limited experience. I've installed exhausts, changed fluids, done brake work, but have not done much under the hood.

Now the issue. I purchased the 1969 coupe in January and live in a cold weather state, so I have not actually had it on the road yet. Not knowing when the oil was last changed, I decided to take advantage of warm weather this past weekend and change the oil. I started the car and pulled it into the driveway to idle and let the oil warm up to temp. While that was happening I was in the garage cleaning/moving some stuff around, and after about 15-20 minutes there was a loud explosion and a cloud of steam that went higher than the house. I immediately ran over and shut the engine off.

I found that the lower radiator hose had blown off where it is clamped to the water pump, and dumped several gallons of coolant (50/50 mix) all over the driveway. Big mess, but okay maybe the previous owner forgot to clamp it tight when he recently hooked up the heater core.

So I re-clamped the hose, and filled the radiator to the top with 2-3 gallons of coolant. I cleaned up the engine compartment as good as I could, but there was still a lot of coolant stuck in places I couldn't get to such as in the fins of the radiator.

Now this is where I started doing some research, as I've somehow gotten to this point without ever having a vehicle with cooling system issues. I couldn't tell if the hose wasn't clamped correctly, or if maybe instead there was a pressure buildup which caused it to blow. I found some information online/here about 'burping' the system to remove trapped air, so I decided since I reattached the hose and filled the radiator that this is something I probably needed to do. I read about several methods, including:

- Leave the radiator cap off, start the engine, and let it run until up to operating temp/thermostat opens
- With radiator cap off, squeeze air out of radiator hoses (lower to water pump, upper to intake)

Last night I decided to try both methods. I removed the radiator cap, started the engine, and let it begin to warm. As it was warming I rapidly squeezed both hoses separately and they just felt like empty hoses. I'm not sure if that's how they were supposed to feel, but wanted to mention that. When I would squeeze, the coolant level would rise in the radiator, but I did not see any big air bubbles come out. Another thing I read online is that when the thermostat opens, I should observe a noticeable drop in the coolant level in the radiator. According to the water temp gauge, I let it warm up to the 200-215 range which means the thermostat should have opened, correct? I never saw the coolant level drop in the tank. Another thing to note is that as the engine was warming up, a LOT of steam started coming off of all parts of the radiator. Am I correct in thinking that this is just all of the trapped coolant in the fins from my first incident?

After 5-10 minutes, the coolant started rising in the radiator, and eventually started overflowing from the radiator fill neck. I decided this was enough for then and wasn't prepared for the mess (was in the garage), so I should shut off the engine. You may see where this is going, but I had no idea what was coming. As soon as I shut off the engine, it PUKED what looks like several gallons of coolant out of the radiator fill and onto the fender/garage floor/engine compartment. Quite the mess and steam room. Frustrated, I cussed everything out and went inside for the night.

I do not know much about electric fans, but the electric fan never came on during any of this. Not sure if this is an issue, but wanted to point it out.

If you made it this far, thanks for reading. Looking for any guidance as far as what you think the issue may be, what I need to test/replace, and how to do that. Some items I've read about online are:

- Faulty thermostat that is stuck shut
- Faulty water pump

Not sure if those match any of my symptoms, but I'd prefer to not just throw money around chasing the problem.

Thank you for any insight!

 

Hi K,
BIG MESS!
I'll start with the MOST obvious…. since it has an electric fan…. is there ANY chance that the belt that drives the water pump isn't in place?
Regards,
Alan

 

Put the hose back on and make sure the clamp is snug. Fill the system cold (just use distilled water for the test, don't waste AF). Put the radiator cap back on. Also change out the thermostat; they're cheap. Start her up and try again. Visually inspect to be sure neither of the radiator hoses is collapsing. Monitor the temp gauge and the fan while it's warming up. If it hits 220 and the fan isn't running, you have a problem there. If the fan comes on but temperature doesn't stabilize, it might be a bad water pump. There's also an outside possibility the radiator is too small. I once saw a guy change to a more radical cam, and that caused the car (not a Vette) to overheat. The only cure was a larger radiator. Again, this isn't likely (especially being as it has an aluminum radiator), just something to keep in mind if all else fails.

 

Its the e- fan. Make sure it even works by running power directly to it, bypassing the relay, temp switch, fuse, etc. Then work your way back to the 12V source to find the problem.

 

Thanks for your reply. I can confirm that the water pump belt is in-place and the pulley seems to be turning just fine w/ no belt slippage.

 

Do this first before you start tearing into anything else.

 

You should not be able to squeeze the lower hose. There should be a spring in that hose. As far as the level rising and coming out the top is normal. That's what the cap is for. It should let a little water into the overflow tank, maybe a 1/2 gallon at the most. You should have seen the water circulating in the radiator with the cap off and then it should start rising. This is normal and tells you the thermostat is opening. If it fills the tank or starts pumping out steam, you may have a head gasket leak. Pulling plugs will show a very clean plug in the cylinder that's leaking.

 

Any recommendation on specific thermostat to install? I know several factors may contribute to that decision, so please let me know if you need any more info. No clue what * thermostat is installed now.

I can try to look for a model/part # on the radiator when I am home later. Thanks

If the fan is designed to come on at 220* there is a chance that I did not let it get that hot yesterday. I will refill with distilled water and let run to temp (with radiator cap on this time!)

It's a little unnerving to see the entire radiator start steaming when the car is warm. Am I probably correct assuming that this was just the spilled coolant burning off from the initial incident? Because if it all burned/steamed off from the initial incident, yesterday's secondary incident made just as big of a mess and there's coolant all in the radiator fins again. Tried blowing it out with compressed air with little success.

 

Could definitely squeeze the lower radiator hose. I actually wrote down the part # from the sticker that is still on the hose. It is a Gates 20811 hose. Looking this up on Jegs (link) it says No spring. As long as the system is close to empty, should I swap this out now for a hose with spring? I did not see any collapsing but want to have the correct type of hose in there for the long term, so if it's best to change now I am okay doing that. Please recommend a specific hose if you know of one. Thanks

 

Try this hose but call first
https://willcoxcorvette.com/corvette...utomatic-68-72
here's a thermostat
http://www.summitracing.com/parts/mrg-4364

 

I always buy 180 thermostats unless I know for sure that my car needs something else. Also, the reason I said 220 is that the fan thermostat should come on around 200. I was trying to account for the possibility of some degree of inaccuracy in both the thermostat and the temp gauge. It's difficult to know about the radiator steaming without seeing it. My gut feel is that it's only the spillage evaporating. In fact, if there's AF all over, I'd wash it down with a garden hose before getting it hot again.

 

That's just coolant on the radiator fins, hose it off and it will steam one last time from water drying. Don't worry about a spring in the lower hose, it wasn't sucked flat when it blew off, lol! The car was at idle, high RPM can suck them closed, but that's not the immediate problem.

 

Thanks for the direction guys, when I have some time I am going to try to figure out if the fan is faulty.

Beyond all of this I am concerned about any other damage that was done when the original hose/clamp blew (e.g. blown head gasket). Pulling the dipstick I do not detect any AF on the dipstick, and there is no noticeable white smoke coming out of the sidepipe exhaust. Have not had a chance to pull the drain plug to really get a good look at the oil, but my fingers are crossed that there was no real damage done.

Thanks again and I will come back to update this thread with findings/questions

 

I think they stopped putting springs in hose awhile back.

Good luck,

Frank

 

Any thoughts as to why it blew to begin with? Other than a loose clamp, what would cause pressure to build up so much in the lower hose that it eventually blew off where it's connected to the water pump?

 

Sounds like stuck shut thermostat .remove it fill with water run re check

 

I've never seen a hose blow off like that. In fact, they're supposed to stay on even if things get so bad that the pressure relief on the radiator cap blows. I think you built up a little more pressure than usual, and the hose blew off because it wasn't tight. I suggest that you not worry about any of this yet, especially if the oil looks OK. Focus on getting it to stay cool.

 

Because the fan didn't turn on, the coolant boiled (and the radiator cap probably didn't open). The excess pressure found the weakest link.

 

interestingly i dont need any "burp procedures" on my 1999. is that an issue with later cars? why?

(i of course tried running it on a slope, but it made no differece whatsoever.)