Topic: Coolent expansion tank problem
in Forum: C3 Cooling and Heating Systems
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HOT SPRINGS NATIONAL PARK, AR - USA
Joined: 11/12/2003
Posts: 190
Vette(s): 1978 (25th Annv. Edition)Red, Black interior, 4-Speed Transmission, L-82, Power & Air, Very Rare Option Package(Only 145 Red 1978s with a 4 speed trans) & Very Original Car, with original Window Sticker, Bill of Sale and all documentaion.
Yesterday on an 80 mile trip to a car show the inflow/out flow tube my coolent expansion tank on my 78 melted and produced a small hole leaking coolent.
The car never over heated nor did have any other problems while driving it!
I replaced this coolent tank 3 years ago because of a simular problem and have had no problems with it until now.
Looking at the distance from the exhaust manifold I can't see where heat from it could have caused the hole to melt. So I can't figure out why this happened!
Has anybody else had this problem before?
What was your solution to this problem?
I am ording a new expansion tank today and the fix is only a little bit of a pain, but I really do not want to do this again.
Can any of the members give me your thoughts? I would appreciate any and all help!
John D. Grant "Corvette; Cure for the common mid-life crisis!"
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Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
John, one possibility is there might be steam going thru the tube, and melting it. Normal, HOT coolant wouldn't do that, unless the plastic is really thin, or the wrong type. I can't see the exhaust doing it either, or it would prolly do it every time you take it on a trip.
Perhaps it just had low coolant, for some reason, and it started puking steam into the bottle, instead of coolant...
That's the only thing I can think of...
What pressure rating does your radiator cap have, and do you know for sure it's holding that pressure?
Perhaps it just had low coolant, for some reason, and it started puking steam into the bottle, instead of coolant...
That's the only thing I can think of...
What pressure rating does your radiator cap have, and do you know for sure it's holding that pressure?
Joel Adams
C3VR Lifetime Member #56 
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Former Member
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HOT SPRINGS NATIONAL PARK, AR - USA
Joined: 11/12/2003
Posts: 190
Vette(s): 1978 (25th Annv. Edition)Red, Black interior, 4-Speed Transmission, L-82, Power & Air, Very Rare Option Package(Only 145 Red 1978s with a 4 speed trans) & Very Original Car, with original Window Sticker, Bill of Sale and all documentaion.
I will try to post a picture tomorrow from my office. I only have dial up at home.
Joel, it is a 15 lb cap from Ecklers. I also replaced it 3 years ago when I replaced the tank also from Ecklers. I think I will order the new one from Mid-America, there catalog says it is heavy duty!.
Steam must be the problem! Nothing else could be hot enough. A weak cap would surely let steam out. I was traveling aroung 85 mph for about 60 miles and the motor was not overheating but was running warmer than normal.
The radiator was completely full, so a weak cap has to be it! I checked the fluid after discovering the leak when it cooled down enough.
I think you figured it out, a weak radiator cap! Bravo! 
Thanks for coming through once again! I appreciate your help very much.
John D. Grant "Corvette; Cure for the common mid-life crisis!"
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
A cap that is not sealing well, or a small leak in the hose from the rad to the overflow, will allow air into the cooling system, which will eventually turn to steam as it flows out of the rad into the catch-can(overflow).
A bad cap may, or may NOT actually leak to the outside, either. They will usually leak to the outside, but not always, so just not having a tell-tale leak is not a guarantee the cap is good.
I hope it's that simple(just a cap), John.
A bad cap may, or may NOT actually leak to the outside, either. They will usually leak to the outside, but not always, so just not having a tell-tale leak is not a guarantee the cap is good.
I hope it's that simple(just a cap), John.
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
To me this is a highly unusual situation. In order for the steam or vapor to be hot enough to melt plastic it seems it would have to be hotter than normal, (195-200). I've seen cars puke into over flow at 260+ and not melt the bottle. Does the o.f. tube feed from the bottom or the top? If from bottom the coolant would keep it from getting hot enough to melt. My .02
Former Member
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HOT SPRINGS NATIONAL PARK, AR - USA
Joined: 11/12/2003
Posts: 190
Vette(s): 1978 (25th Annv. Edition)Red, Black interior, 4-Speed Transmission, L-82, Power & Air, Very Rare Option Package(Only 145 Red 1978s with a 4 speed trans) & Very Original Car, with original Window Sticker, Bill of Sale and all documentaion.
Here you can see the place where the tank melted. Since it fills from the top, I can only guess that steam is the culprit. Since the gauge reads within normal ranges when this happened I cannot see how it is making it unless the radiatior cap is bad. Do you guys have any other thoughts?
There was coolent in the expansion tank that was about 1/2 and inch above the cold line. Could that have been a part of the cause?
Enquiring minds want to know!
John D. Grant "Corvette; Cure for the common mid-life crisis!"
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
Hmmmmm....that kinda looks like an external heat issue.
Since you are replacing the tank, once you get it off, look and see if you can tell if the inside of that area is damaged. You might not be able to see down there, but it would be interesting to know if it was or not...
Is this the exact same failure the other tank had?
Terry is right about the coolant keeping it from being hot enough to melt, since it is a bottom feeder....unless it's drawing ALL of the coolant out of the bottle on those high-speed runs...
How far away is the exhaust from that part of the tank? You got headers, or iron manifolds?
If headers, it's possible that the cylinder closest to that part of the puke tank is running lean, which would make that particular header tube hotter than the others...it's a long-shot, but it's all I got!
Since you are replacing the tank, once you get it off, look and see if you can tell if the inside of that area is damaged. You might not be able to see down there, but it would be interesting to know if it was or not...
Is this the exact same failure the other tank had?
Terry is right about the coolant keeping it from being hot enough to melt, since it is a bottom feeder....unless it's drawing ALL of the coolant out of the bottle on those high-speed runs...
How far away is the exhaust from that part of the tank? You got headers, or iron manifolds?
If headers, it's possible that the cylinder closest to that part of the puke tank is running lean, which would make that particular header tube hotter than the others...it's a long-shot, but it's all I got!
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Man John I wish I had an answer for ya. Been in the radiator business for 37 years and I've seen melt down on the OF tank, but only when the temp pegged out. For your system to be running normal temp. and cause that burn is beyond me. I can't figure out why the tank isn't warped from the heat. Can you tell if its burned from the inside? No 1/2 over cold will not cause that. I would make sure your Gage is working right and your not overheating and causing that hot of vapor. Wish I could be more help.
Former Member
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HOT SPRINGS NATIONAL PARK, AR - USA
Joined: 11/12/2003
Posts: 190
Vette(s): 1978 (25th Annv. Edition)Red, Black interior, 4-Speed Transmission, L-82, Power & Air, Very Rare Option Package(Only 145 Red 1978s with a 4 speed trans) & Very Original Car, with original Window Sticker, Bill of Sale and all documentaion.
It has the original cast iron manifolds and the distance is far enough you would not think it would melt it. But if it did it you would think that it would warp the tank and not melt a very small spot.
The tank appears to have melted from the inside from a single event.
Once I replace the tank I will cut it open and look at exactly what happened. I will post another picture at that time. Hopefully I will get it done this weekend.
I plan to put in some "Water Wetter" again when I replace the tank. I have had that in the car until this year when I flushed and refilled with new 50/50 antifreeze mix. I had no problems while WW was in the car. I have had it in the car since the original problem occured and just failed to put it in this year on the flush and fill. 
I will go by my mechanic and check out how hot the car is running and make sure the temp gauge is accurate. I am running a 180 degree thermostat, so I still think the main culpret is the radiator cap.
Thanks for all of the suggestions and help. I will post photos and comment after the tank is cut open. Thanks again!
John D. Grant "Corvette; Cure for the common mid-life crisis!"
in Forum: C3 Cooling and Heating Systems
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