How much coolant overflow is normal?

[gunnibronco]

I'm driving my 72 around town more. It's nearly 100* out. Around town, normal driving the temp was under 190*. I let the truck idle for a few minutes while I opened up my garage to park it. Sitting still the temps jumped to 200*+, and it was pushing coolant out the nipple under the radiator cap (new cap last summer Gates 13#). I feel like the cooling system is fine, the cap is releasing pressure when hot, and everything is working normally. It seemed like a lot of coolant, there was a decent spot in the driveway and on the garage floor after I parked it. I popped the hood and there was a steady dribble coming from the overflow nipple. How much is normal? Were all the cars puking coolant like this in 1972? I can see why they mandated overflow cans, I've never owned a vehicle without one.

 

[BronCowie]

I would recommend a coolant recovery tank. They work great at what they are intended to do.

 

[gunnibronco]

I would recommend a coolant recovery tank. They work great at what they are intended to do.

After seeing this today I'm considering adding one. I'm working on a *close to stock* build, but adding an OE style one isn't out of the question.

 

[DirtDonk]

You could pretend it’s a very late 72 model, and it might’ve had one from the factory.
Since 73 was the first model year that got the overflow tank, many late 72s got a lot of 73 features.
Especially if your VIN had a Q in it!

 

[Broncobowsher]

I recall the factory non-recovery cooling systems called for an air space above the cold water level. Room for thermal expansion. Fill it and it will spit coolant out.

 

[DirtDonk]

And while, yes, that is kind of normal, it depends on what else might be going on.
Your new radiator cap might be releasing earlier than 13 psi for example.
We’re pretty skeptical about new parts around here. Also could be that your gauge isn’t showing the full temperature.
Perhaps there’s a little hotspot in the engine creating extra heat that’s not registering on the gauge. That would certainly puke more than normal.
Generally speaking, they puke when they’re full, until it reaches a certain point below full, where it would not puke as much each time.
That’s an unfortunate thing, and that sometimes it gives you a false sense of security and not check your fluid level in a long time.
Because eventually, you can lose a great deal of coolant.

So it doesn’t hurt to double check some of those other things. Verifying actual temperature seems a good start.
But a recovery tank is always a good idea no matter what anyway.

 

[DirtDonk]

I recall the factory non-recovery cooling systems called for an air space above the cold water level. Room for thermal expansion. Fill it and it will spit coolant out.

Beat me to it! I was halfway through my second post and got sidetracked with restaurant duties. Seems like everybody had a late night craving for Mongolian barbecue!

 

[gunnibronco]

All good suggestions. It makes sense to "under fill" the radiator to leave space for the thermal expansion. According to my Harbor Freight IR temp gun the gauge matches the actual temp within reason. One point to my drive was to compare my newly installed used water temp gauge. I'll see if I can find a fill level that keeps things happy with minimal overflow. If not I might add an overflow tank and pretend it came from the factory. It's not a factory correct restoration. It's lifted with power brakes and probably power steering soon. I just want it to be a nice reliable driver, but to maintain the old school engine compartment.

Thanks

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[Brush Hog]

New radiator caps are crap (including the one that came with my new radiator). I went through three or four before I found one that would keep pressure in radiator so over flow tank would work. All the others allowed it to puke around the cap everytime I turned the motor off.

 

[Steve83]

It makes sense to "under fill" the radiator to leave space for the thermal expansion.

No, it really doesn't with a vented cap.

The cooling system takes ~4 gallons, which when going from 70-220°F expands by ~16oz (~3%). But any air in the system expands ~10x as much as the coolant, so the less air (which will NOT collect at the radiator cap) the better because more air will just push more coolant out. If you minimize the air in the system, you also minimize the necessary tank size to catch & return that coolant when the engine cools off. Even if you really try, you'll never get all the air out, but that should be your goal.

Also remember that the engine block, radiator, and hoses also expand as they get hotter, making a little more room for the expanding coolant. But those numbers are harder to calculate, and not really significant. Most of the change in volume is absorbed by the rubber hoses stretching, the air compressing (to make the necessary pressure), and rest is temporarily ejected to the overflow tank.

 

[gunnibronco]

New radiator caps are crap (including the one that came with my new radiator). I went through three or four before I found one that would keep pressure in radiator so over flow tank would work. All the others allowed it to puke around the cap everytime I turned the motor off.

I'm very suspect of any new parts as well. Unfortunately, it's become necessary the last 10+ years. Mine isn't leaking around the cap, but from the overflow nipple. That's not saying the cap is maintaining 13 psi. Weird side not, I bought a Gates cap according to my Rock Auto receipt, but it is stamped MotoRad. Not sure what that means.

Edit. I guess MotoRad is making caps for Gates.



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[gunnibronco]

No, it really doesn't with a vented cap.

The cooling system takes ~4 gallons, which when going from 70-220°F expands by ~16oz (~3%). But any air in the system expands ~10x as much as the coolant, so the less air (which will NOT collect at the radiator cap) the better because more air will just push more coolant out. If you minimize the air in the system, you also minimize the necessary tank size to catch & return that coolant when the engine cools off. Even if you really try, you'll never get all the air out, but that should be your goal.

Also remember that the engine block, radiator, and hoses also expand as they get hotter, making a little more room for the expanding coolant. But those numbers are harder to calculate, and not really significant. Most of the change in volume is absorbed by the rubber hoses stretching, the air compressing (to make the necessary pressure), and rest is temporarily ejected to the overflow tank.

I'm not sure how many ounces I'm losing but it's a decent puddle on the garage floor. Seems like too much. Plus I have a dufus dog that taste tests just about anything he can. Since everything seems to be operating well, my guess is that if something is wrong it's the cap, but I'm not sure. That's cheap enough to swap out.

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[Jetfixr320]

I recall the factory non-recovery cooling systems called for an air space above the cold water level. Room for thermal expansion. Fill it and it will spit coolant out.

I didn't know this. But, its what I started doing on my 60's cars, Fill it and let it puke a little out the overflow, let it find it's happy spot.
Added overflows later.

 

[DirtDonk]

Hey gunni, check the lower driver’s corner of your core support. If it’s a late enough 72 you already have the bump-out for the larger power steering box.
Lots of later build 72s, while still having manual steering, manual transmission, manual brakes, and the old style air cleaner, with no radiator overflow bottle, still got the updates getting ready for the 73 model year changes.

 

[Steve83]

I have a dufus dog that taste tests just about anything he can.

If he tastes more than an ounce of coolant, he'll get sick enough to die in about an hour.

...my guess is that if something is wrong it's the cap, but I'm not sure. That's cheap enough to swap out.

Cost should not be a diagnostic consideration, but guessing isn't diagnosis. Call the local parts stores to find which one has a coolant pressure test kit you can borrow in the store to test the cap. But don't buy cheap caps - buy genuine Ford/MC. Shop for this PN:

Amazon.com: Motorcraft RS62 Radiator Cap : Automotive

Buy Motorcraft RS62 Radiator Cap: Standard - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

 

[nvrstuk]

... and to add to Steve's post. It's an absolutely HORRIBLE slow death for dogs. My son's dog was intentionally poisoned and we didn't know what it was affecting her until about 12 hrs into the non-stop heaving. Vet tried everything they could but it was gruesome... and I've seen a lot of farm animals with guts trailing out their sides and other not so nice stuff happening to them and this was/is the worst ever.

X2 on the test kit. OReilly's let's you borrow all that stuff for free.

Just cause it has a Motorcraft part # and a Motorcraft box doesn't mean anything anymore. My Ford part # waterpump in a Motorcraft box had a white sticky on the back side of it with the word "CHINA" on it...

I'm on my 2nd TPS in 3 months... parts are garbage, even new "OE" parts... hence my thread on going back to Qjet... lol

 

[gunnibronco]

Hey gunni, check the lower driver’s corner of your core support. If it’s a late enough 72 you already have the bump-out for the larger power steering box.
Lots of later build 72s, while still having manual steering, manual transmission, manual brakes, and the old style air cleaner, with no radiator overflow bottle, still got the updates getting ready for the 73 model year changes.

It's the 72 core support, no bump out for power steering gear box. It's a P vin built in April 72, before all the weirdness.

 

[gunnibronco]

If he tastes more than an ounce of coolant, he'll get sick enough to die in about an hour.

Cost should not be a diagnostic consideration, but guessing isn't diagnosis. Call the local parts stores to find which one has a coolant pressure test kit you can borrow in the store to test the cap. But don't buy cheap caps - buy genuine Ford/MC. Shop for this PN:

Amazon.com: Motorcraft RS62 Radiator Cap : Automotive

Buy Motorcraft RS62 Radiator Cap: Standard - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

I'm super careful with both my dogs and all the toxic stuff around the shop. About 30 years ago I had a friend who mistakenly took a swig of RV antifreeze, thinking it was kool aid or something. He got treatment, and I got a pretty serious education on antifreeze, way over and above "don't drink it".

In regards to the rad cap, or any other parts now-a-days, I only buy from reputable sources (no amazon, no ebay), and I try to buy a good name brand (Rock Auto/Gates). But that is no guarantee of quality anymore. It makes repair and diagnosis so much fun!/sarc/

 

[gunnibronco]

... and to add to Steve's post. It's an absolutely HORRIBLE slow death for dogs. My son's dog was intentionally poisoned and we didn't know what it was affecting her until about 12 hrs into the non-stop heaving. Vet tried everything they could but it was gruesome... and I've seen a lot of farm animals with guts trailing
ut there sides and other not so nice stuff happening to them and this was/is the worst ever.

X2 on the test kit. OReilly's let's you borrow all that stuff for free.

Just cause it has a Motorcraft part # and a Motorcraft box doesn't mean anything anymore. My Ford part # waterpump in a Motorcraft box had a white sticky on the back side of it with the word "CHINA" on it...

I'm on my 2nd TPS in 3 months... parts are garbage, even new "OE" parts...

That is a horror story. I'd be absolutely heart broken if something like that happened to my dog or anyone's pet. I'd be boarderline murderous if someone intentionally did that to my dog.

I'll check on a test kit at Oreilly's and see what's happening.

The issue with bad parts is all too common. Even trying to buy OE or just a good name brand when OE isn't available (Delphi, Bosch, Gates, etc). I installed a Bosch relay in my step son's car (fuel pump relay), out of due diligence when replacing a fuel pump. It lasted less than 6 months and had us chasing our tails trying to figure out what was wrong. Old original relay is reinstalled and still working. It's a nightmare.

 

[DirtDonk]

It's the 72 core support, no bump out for power steering gear box. It's a P vin built in April 72, before all the weirdness.

Gotcha. I have two friends that had '72's that did not have any of the '73 stuff. And two friends BOTH of who's '72's had much of the '73 stuff.
I'll have to go back and see if I can find out what months they were built in.

Paul