Adding aftermarket coolant recovery tank to 68-72 big block AC car

[Mark E.]

The idea is to add a coolant recovery system to eliminate air in the system and coolant loss. I have a 1970 454 AC car but I'm thinking the challenge (engine compartment layout, lack of under hood space) is similar for all 68-72 big block, AC cars.

Does anyone know about a clean, well done installation? Photos, detailed description and list of parts would be useful.

As you guys know, a coolant recovery system was added by Chevrolet in 1973.

[Michael W.]

Re: Adding aftermarket coolant recovery tank to 68-72 big block AC car

An add-on coolant recovery tank would be no more than a band-aid covering up an underlying problem:

1) overfilled rad
2) weak/incorrect rad cap
3) overheating due to problems with radiator, timing, thermostat, etc etc.

The car didn't need a tank when new, shouldn't need one now.

[Patrick H.]

Re: Adding aftermarket coolant recovery tank to 68-72 big block AC car

All you would gain is that whatever coolant came out of the overflow wouldn't end up on your garage floor. Unless you kept the overflow pressurized and moved the cap to the overflow tank (think the base motor small block) you aren't gaining anything nor improving the system.

The vast majority of coolant loss is due to overfilling of the system. Drive the car and the excess will puke out. When it finds its correct level, it stops. I saw it happen again this past weekend on the way to our Chapter Meet in a car that was relatively freshly filled.

[Donald A.]

Re: Adding aftermarket coolant recovery tank to 68-72 big block AC car

Hmmm. Interesting post. I have same car. No issues but did experience what the post above states. After doing a radiator fluid change my car puked a little and that made me worried. Then I checked inside the tank to discover that it still had fluid but nit as much as I had filled. So as stated it found its equilibrium and then has not done it since.

Are you having a legit overheating problem ? After puke and cool down is there any fluid in the tank?

[Douglas L.]

Re: Adding aftermarket coolant recovery tank to 68-72 big block AC car

The previous owner added a recovery tank to my 68 L36 car. Thought about removing it but I like the idea of getting rid of the headspace in the radiator. I dont know if it matters but it seems like if you can get rid of the air in the radiator there would be less potential for corrosion. He used a parts store tank and attached it with screws to the passenger side inner fender. Luckily, he drilled the holes in a place that would be mostly out of sight with the tank removed for judging. Works well, whatever it pukes out when hot get sucked back in when it cools and rad stays totally full all the time.

[Duke W.]

Re: Adding aftermarket coolant recovery tank to 68-72 big block AC car

A coolant recovery tank is a good idea, but as previously suggested you should check your radiator cap to verify that it releases near the 15 psi spec. If you do install a coolant recover tank, install it as high as possible.

If the engine is running excessively hot, the radiator may need a rod out or recore due to deposit buildup in the tubes, which reduces the radiator's ability to reject heat.

Your '70 has ported vacuum advance. Converting to full time with a B26 VAC will considerably reduce heat rejection to the coolant system in typical around town driving in traffic. If it's a TH400 it may need a B28 to meet the Two-Inch Rule idling in Drive with the compressor engaged.

The OE centrifugal advance only has 22 degrees, and it's lazy. Remember the spark advance map was set up for emissions, not performance or fuel economy, and the emission oriented map increases EGT, which causes more heat rejection to the cooling system. Total centrifugal of 28-30, in by 3000-3500 would be better with 8-10 initial.

Of course you should verify with a dial-back timing light what it really is and compare to the data in the AMA specs and CSM.

Duke

[Michael W.]

Re: Adding aftermarket coolant recovery tank to 68-72 big block AC car

if you can get rid of the air in the radiator there would be less potential for corrosion.

The headspace in the rad is actually filled with 'coolant vapour' and not really air- not that either is all that corrosive. If air was a serious problem, rads would quickly rot from the outside in.

Best strategy is fill the rad to the full line embossed on the side tank and monitor any losses. If none, then all is normal. If yes, track down the actual problem.

[Mark E.]

Re: Adding aftermarket coolant recovery tank to 68-72 big block AC car

Thanks for the input guys.

One clarification: I'm not doing this to fix an overheating problem; my LS5 runs fine. Coolant temp typically stays near the thermostat's setting of 180 degrees, but may drift closer to 200 in traffic with AC on. Certainly not a problem.

But a coolant recovery system has significant benefit: air is eliminated in the system (benefit: with a proper mix of clean coolant this eliminates virtually all corrosion; no aeration means more efficient cooling) and there's no loss of coolant (benefit: no mess on the ground; changes in coolant level due to a leak are more detectable; no discharge of toxic liquid to the environment).

I've owned a lot of pre-73 GM cars and found that adding a recovery system has helped maintain a clean, efficient cooling system with components that last longer. There's a reason GM adopted it for newer cars.

Anyway, I'm still interested in learning about any installations out there for these cars. With the limited space, it's more involved than with most cars.

Thanks again.

[Michael W.]

Re: Adding aftermarket coolant recovery tank to 68-72 big block AC car

But a coolant recovery system has significant benefit: air is eliminated in the system (benefit: with a proper mix of clean coolant this eliminates virtually all corrosion; no aeration means more efficient cooling) and there's no loss of coolant (benefit: no mess on the ground; changes in coolant level due to a leak are more detectable; no discharge of toxic liquid to the environment).

.

Mark-

Not to start a debate but the vast majority of Corvettes prior to '73 have no recovery tank and do not suffer any of the ills you've mentioned above.

[Mark E.]

Re: Adding aftermarket coolant recovery tank to 68-72 big block AC car

Your '70 has ported vacuum advance. Converting to full time with a B26 VAC will considerably reduce heat rejection to the coolant system in typical around town driving in traffic. If it's a TH400 it may need a B28 to meet the Two-Inch Rule idling in Drive with the compressor engaged.

The OE centrifugal advance only has 22 degrees, and it's lazy. Remember the spark advance map was set up for emissions, not performance or fuel economy, and the emission oriented map increases EGT, which causes more heat rejection to the cooling system. Total centrifugal of 28-30, in by 3000-3500 would be better with 8-10 initial.Duke

This brings up a separate topic of interest: ignition timing. There are a lot of posts on the various Chevy/Corvette forums plus other information about this, so I don't see a need for a separate thread.

With that said, my 1970 LS5 (and many other Chevys around this vintage) does not have ported vacuum but rather uses a Transmission Controlled Spark (TCS). TCS blocks manifold vacuum to the vacuum advance except in top gear or when the coolant exceeds a certain temperature. I have the original 7040205 Q-Jet (49 state version) but run the car with a similar vintage 7040505 (part of the NA9 EEC system). One reason I'm running it is that it has an additional vacuum line on the front which is ported. This line originally attached to the NA9 vapor canister (which my car does not have), but I use it as an option for vacuum advance tuning.

The stock set up with TCS and 4 degrees BTDC initial and less than 30 degrees total centrifugal is a bit "lazy" (as Duke says). This car idles and performs much better (and cooler) with 10-12 degrees of initial and 36-38 degrees total centrifugal advance. So after bypassing TCS and recurving the distributor, the options I play with:
- Installing a variable VA so I can adjust it.
- Run the VA with manifold vacuum. This requires modest (4 deg) initial centrifugal advance since the VA adds about 8 degrees at idle.
- Run the VA through ported vacuum (which the 7040505 provides). This requires 12 BTDC initial centrifugal advance, less total distributor advance plus a different VA setting.

So I play with initial and total centrifugal advance first to dial in WOT timing, then add VA for cruise and part throttle performance/economy.

The TCS system is still there so I can hook up the lines whenever I want to look original.

One of the things I love about these vintage cars is you can play shade tree mechanic and have some fun.

Best,

[Mark E.]

Re: Adding aftermarket coolant recovery tank to 68-72 big block AC car

I don't know if they are "ills", but pre-73 Corvette do have air in the cooling system and do burp coolant to the ground from time to time.

I'm just saying that a coolant recovery system does provide benefit, which GM also realized beginning in 1973.

A similar analogy might be the introduction PCV. Older cars without PCV may not have "ills" but don't gain its benefits- less condensation in the oil, less susceptibility to sludge. With that said, I doubt I would remove the draft tube and add PCV to an original Corvette either.

[Jim T.]

Re: Adding aftermarket coolant recovery tank to 68-72 big block AC car

Having my original owner 1970 350 with factory air conditioning, I learned just a couple weeks after buying my Corvette that full time vacuum by passing the original installed system was the way it would stay. It remains that way today. Gas mileage increase in city and reduction in engine temperature were benefits. I have used a coolant recovery on my 1970 for many, many years. Don't remember exactly when I installed it. I removed the side grille to install the coolant recovery tank, its plastic and let the base of the tank rest on the metal plate.

[Joe L.]

Re: Adding aftermarket coolant recovery tank to 68-72 big block AC car

Mark-

Not to start a debate but the vast majority of Corvettes prior to '73 have no recovery tank and do not suffer any of the ills you've mentioned above.

Mike-------


Not the majority but ALL Corvettes prior to 1973 were not originally equipped with a coolant recovery tank.

[Joe L.]

Re: Adding aftermarket coolant recovery tank to 68-72 big block AC car

The vast majority of coolant loss is due to overfilling of the system. Drive the car and the excess will puke out. When it finds its correct level, it stops.

Patrick-------


Yup.

[Joe L.]

Re: Adding aftermarket coolant recovery tank to 68-72 big block AC car

The headspace in the rad is actually filled with 'coolant vapour' and not really air- not that either is all that corrosive. If air was a serious problem, rads would quickly rot from the outside in.

Best strategy is fill the rad to the full line embossed on the side tank and monitor any losses. If none, then all is normal. If yes, track down the actual problem.

Mike------


All 1969-72 Corvettes with big block do not use a radiator with a filler on one of the side tanks and, thus, there are no fill marks on the side of the side tanks. Instead, they use an external supply tank like many small block cars. The configuration of the system being what it is, I doubt that there is any "headspace" in the radiator as long as the external supply tank has coolant in it.

The external supply tank should not be filled more than half way. If it is, the amount above half will be rather quickly purged out the overflow.