C2 427/390 coolant discharge from overflow tube

[Jerry S.]

I just replaced the radiator in my 66 427/390 with a Dewitts unit. Engine runs as cool as expected for an Arizona summer but for some reason after I shut it down I notice I lose some coolant from the overflow drain tube. Any suggestions to prevent this or is it just normal operation driving in the 100 degree temps?

[Russ S.]

Re: C2 427/390 coolant discharge from overflow tube

It is normal if you have the radiator too full and/or a bad cap

[Mike T.]

Re: C2 427/390 coolant discharge from overflow tube

Jerry - Russ has hit the high points for first things to consider if your radiator replacement was recent. It does take a bit of time to find the right level of coolant in the expansion tank, if that's what's going on here. Maybe it's just a bit overfilled? And, can you fill us in on what might have been going on before the radiator replacement, in other words, were there any cooling issues before the new radiator?

[Tony S.]

Re: C2 427/390 coolant discharge from overflow tube

Hi Mike. No expansion tank on the 66 BB cars. I've had similar issues. I seem to have solved my overflow issue by installing a higher pound cap and not putting my foot into it quite as much to heat up the block. I sure love driving my car though. Tony

[Mike T.]

Re: C2 427/390 coolant discharge from overflow tube

Hey Tony - Of course, I should have picked up on that, seeing yours is a 66. I've been working on my 65 NOM 396 Roadster and seeing the '65 expansion tank on a Bigblock kinda got stuck in my mind. What sorta dash gauge readings are you seeing?
"Not" put your foot into it??? Okay, you're kidding, right :-O?
We've been seeing low to high 90's up here in Prescott, I'm guessing you're somewhere down in the Valley?

[Tony S.]

Re: C2 427/390 coolant discharge from overflow tube

Hey Mike. It was getting up to the puke stage of about 230. The higher rated (non-factory) radiator cap helped. I can keep the temp gauge at about 200-210 now. City driving makes a big difference with windflow. Getting the coolant levels was a little tricky. I had mine filled too high. I'm pretty good where it is now. I do have a modern vacuum can that I can switch out, but I don't want to do that if I can avoid it.

I love driving my car. If you see Kevin Dewitt down your way, tell him hi for me. Enjoy the ride! Tony

[Stephen L.]

Re: C2 427/390 coolant discharge from overflow tube

Tony,
If there is no "expansion tank" on the car, where does the cooling fluid expand to, when heated from ambient?

[Mark E.]

Re: C2 427/390 coolant discharge from overflow tube

Tony,
If there is no "expansion tank" on the car, where does the cooling fluid expand to, when heated from ambient?

If the car has a non-pressurized coolant recovery tank, the pressurized system remains full with virtually no air. Corvette began with this design in 1973.

Without a recovery tank (1972 and older Corvettes), space (air) is needed in the pressurized system for expansion. Some cars feature a separate pressurized expansion tank (e.g. 1970 454), others require air in the radiator tank for expansion (like Tony's '66). If these systems are overfilled, then they puke to the ground like Jerry experienced. When filling one of these systems, I deliberately overfill it, then let it puke as it seeks the correct coolant level.

[Stephen L.]

Re: C2 427/390 coolant discharge from overflow tube

Mark,
I have a coolant recovery tank on my cars. It is a location for the expansion fluids to go to (recovery) when hot and then is sucked back into the system when cool. The idea is to keep that tank at a reduced level (not full) when at ambient temp, allowing for fluid space as the fluid is heated. This eliminates "puking" of fluid on the ground AND keeping the pressurized system full at all times. IF you fill the recovery tank to full the excess will puke on the ground. The EPA folks don't like that. That is why there is a calculated "fill to line" on the side of the recovery tank, to avoid overfilling of the total system.

[Tony S.]

Re: C2 427/390 coolant discharge from overflow tube

Hi Stephen. There's a hose that attaches to a nipple on the upper part of the radiator--just below the radiator cap. When the radiator pukes, the fluid goes out the hose and onto the ground surface. Best, Tony

[Mark E.]

Re: C2 427/390 coolant discharge from overflow tube

Mark,
I have a coolant recovery tank on my cars. It is a location for the expansion fluids to go to (recovery) when hot and then is sucked back into the system when cool. The idea is to keep that tank at a reduced level (not full) when at ambient temp, allowing for fluid space as the fluid is heated. This eliminates "puking" of fluid on the ground AND keeping the pressurized system full at all times. IF you fill the recovery tank to full the excess will puke on the ground. The EPA folks don't like that. That is why there is a calculated "fill to line" on the side of the recovery tank, to avoid overfilling of the total system.

Agreed. We're saying the same thing a bit differently.

[Jerry S.]

Re: C2 427/390 coolant discharge from overflow tube

Thanks to all who replied and sorry I've been slow to respond. I replaced the radiator because my old one sprung a slow leak. The cap I have is a 15# and about a year old. The temp needle stays close to a range between 180 and 210, I rarely see it go much higher unless I come off the freeway and have to sit idling in the off ramp. I've taken the cap off and let the engine run, watching for bubbles. I saw them but also experienced the fluid level rise up to the top of the radiator neck. I shut the engine off before it spilled over and put the cap back on. Now looking for other possible solutions.

[Mark M.]

Re: C2 427/390 coolant discharge from overflow tube

As its been mentioned the system will expand in the radiator tank and overflow until its low enough it won't do it any more. The brass radiator 66-67 427 radiators have a fill line about 4 inchs down from the cap. I drill an 1/8" hole in the thermostat outer edge and jack up the front end and will run the engine to temp to get possible air out. Even after all this, if the car is parked on a hot day with the front right corner lower it sometimes spits out the overflow again. Add to this the factory ported vacuum runs the engine hotter but thats another subject.