help with coolant leak/ overheating 79' 308

You probably need to poke a small adjustable mirror down into the tank, shine a flashlight in there, then you should be able to see whether or not the small tube is present. It was easier for me to check as I had the tank off the car and it was therefore totally empty.

 

I couldn't quite believe this, but having spent time with their technical guys, and with their customer service guys, I placed the order and everything seemed to be fine. McMaster definitely left me feeling as if they're a class outfit with excellent customer service.

BUT WAIT ... 2 or 3 hours later I received an email from some guy telling me that they no longer sell to Canadians other than long established customers. In other words, I'm pooched. I doubt that I'll be able to find these parts from another source in Canada, so I'm kind of back to square one for now. JUST BEWARE -- if you're not in the USA, you probably won't be able to order the parts from McMaster.

 

Newbydude,

Ship the parts to my house and I'll ship them to you in Canada. Problem solved. I tried to PM you but your mailbox was full.

Dan

 

There's several forwarding companies set up to handle that issue.
I've used MyUS.com. Just google US forewarding address for a range of them.

 

I never knew that. You learn something everyday.

 

Simon,
I had to order some stuff from McMaster today, just added your parts to my order. When it comes in I'll reship to you.
'Gards,
Verell

I can't tell for sure, but in in the cooling system dwg in the GT4 WSM, it appears that the pickup tube is there, or at least there are a couple of lines in the right place to be the tube.

Before you go plugging the upper hose, or installing a check valve, HAVE YOUR COOLANT TESTED FOR COMBUSTION PRODUCTS/EXHAUST GASSES. If you don't you're risking masking a head gasket leak that, if not promptly addressed, will cost you big $$ down the road.

 

In the injected cars, there is a vacuum switch in the coolant expansion tank that controls the cold idle device in USA spec cars. When the coolant in the expansion tank reaches a certain temp, the idle speed drops back down to normal. There is a "bleeder" off the water pump that runs a stream of coolant into the top of the expansion tank through that upper thin hose. The bottom of the tank is connected to the rest of the cooling system through a fatter hose. I never thought about what function this design would serve in the carb cars that have no temp sensor in the expansion tank. I'm very curious about this one-way valve thing...shouldn't hurt anything and might be a small design improvement.

One other thing...the oscillation of high to normal temp is classic symptoms of air in the system.

Birdman

 

http://www.ferrarichat.com/forum/showpost.php?p=137862042&postcount=8

 

Here's the latest ... I plugged the upper hose a few days ago and haven't had any problems with my cooling system since. It was easy to burp, and no air has been introduced into the system since plugging the hose. Apart from the initial release of coolant which was caused by brimming the reservoir, the coolant level has remained constant. The car runs at a steady 175 degrees on the highway -- if stuck in traffic the cooling fans turn on and keep everything under control.

Next step will be to introduce the check valve in place of the plug. I'll report back once I know how this works.

 

Sorry, gotta say it....

If plugging the upper hose fixes the problem, why are you replacing it with a check valve that is inherently less reliable than a plug (not to mention more expensive)? Seems like a step backwards, not forwards.

Bob
'78 308GTS
'01 Corvette Z06

 

To be honest with you, this is unknown territory for me (others may wish to chirp in if they know how all of this works) so I cannot see any harm in trying the check valve. Intuitively, I guess I feel more comfortable with the idea that coolant can bleed off into the tank as it expands.

Hey, if it doesn't work, or if the check valve fails, it's only $20 or $30 down the drain. In the scheme of 308 maintenance, this is peanuts of course.

 

There is a large hose from the bottom of the tank that allows coolant to bleed into the tank as it expands. Connects to the water pump housing right next to the connection for the small tube. Don't think that is an issue.

If you are really worried about it, take the tank to a radiator shop and have them extend the tube inside the tank down to a level below the coolant. That is evidently how Ferrari fixed the problem for the injected models.

Personally, I think it was just due to some engineer overdesigning the cooling system. Made a bad decision to add the upper tube in the first place to 'enhance water circulation and even out temperature variations'. Didn't realize that the circulating coolant could go in either direction, causing air to be drawn from the top of the tank. Instead of admitting the mistake, they continued the design for later models, but added the extension tube inside the tank. Sounds like something GM would do. Never admit a poor design. Patch it. Modify it. But don't admit it.

I wouldn't go the check valve route simply because this is not a pressure connection that would exercise the valve to make sure it stays working. Minimal pressure difference between the two sides. Depending on the design, it could stick in the open position for various reasons. If it is a differential pressure type valve, it will always be closed, and be no better than a plug (until the spring fails). Like the original design, it seems like a needless complication.

Plug it and forget it. Just my .02

Bob

 

Interesting.

Has anyone confirmed that the check valve helped?

I was thinking the air was coming from the bottom hose sucking air out of the tank during braking/acceleration/cornering .... plugging the top hose would stop this from happening since you're preventing circulation thru the tank so shouldn't suck anything out of there anymore .... my tanks don't have an extension going down into the coolant level as described ... I don't think it sucks air back thru the top hose like some are theorizing.

I was thinking of putting a catch tank on the end of the overflow hose so she'd puke the water out when hot but then suck it back in when it's cold like a lot of cars have.

Plugging the top hose sounds easier though. BTW I think someone mentioned this ... F might of wanted the water ciruclating thru the tank to give the sensors on the tank accurate engine coolant temps perhaps?

Cheers

 

I would like to continue the discussion about the two hoses going to the expansion tank, what their purpose is, how they work, what can go wrong, and how to diagnose/fix problems in that area.

I have a persistent problem with air in my cooling system and I am beginning to suspect that it might have something to do with the expansion tank and how these hoses integrate into the cooling system. I had the expansion tank tested for leaks when my radiator was re-cored and it was not leaking. Verell has suggested that there could be some sort of internal air leakage. I think what he is suggesting is that a tube internal to the tank has a leak above the coolant level. (See picture below) Others have suggested that the problem occurs due to hard cornering and such. If that’s the case then why did Ferrari decide to lay the tank flat on the later models? That seems like it would make the problem worse.

If I understood Verell’s idea correctly, is there a way to test for an internal leak like I think he is describing? I understand the necessity for the expansion tank but I don’t understand the why it needs two hoses. Can someone explain that to me?
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There was another thread on this subject recently. It seems that most of the experts agree that the upper hose is there for a reason and that plugging it is not the proper way to resolve the issues with air getting into the system. It was suggested that if plugging that hose solves your problem that you are merely masking another problem somewhere else in the system.

That being said, I had the same problem as just about every other carb car owner I have talked to. I solved it by plugging the upper hose to the expansion tank. I know the experts will soon be here to tell me I am wrong, but my car is running better, cooler and doesn't puke coolant every time I pull in somewhere.

I believe...let me say that again....I BELIEVE..... that the air gets into the system through the upper hose coming off the expansion tank. I've been told on later cars that there is an internal tube like in the picture in the post above. On the other hand, the vertical tanks like on our carb cars doesn't appear to have the same internal tube. At least my tank does not and I have yet to hear any first hand accounts of one actually being there.

Now obviously the best solution would be to install a tube (and in the back of my mind I remember someone doing exactly that I believe), but in the mean time I have plugged the upper hose and am proud of it. I see no negative effects from having done so and please don't tell me it's because I have neglected some other part of my cooling system.

Sorry for the rant, but there it is, it's off my chest now!!!

 

After looking at my car for a while I came up with the diagrams below. They represent my current understanding of the cooling system. The Expansion tank is still a black box I don't know what goes on in there. It looks to me like there is a constant flow through the tank so a single hose would put an end to that. I think there is a temperature sensor on or under the expansion tank so without that flow it would take quite a while to get up to temperature. Has anyone here ever dissected one of these expansion tanks? Is it possible some of the flows get reversed under some conditions? It appears to me that there is flow through the expansion tank under all conditions.
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But you are talking about a QV 308 correct? There are no sensors in an older carb car expansion tank and it is vertical not horizontal like yours. Therein lies the rub! The second hose may indeed serve a vital function on the newer cars. On the older cars though, without some sort of tube to keep the upper hose in contact with the water inside the expansion tank, it will suck air into the system. I don't see any way around it. Maybe I'm oversimplifying things but I don't think so. Water and air are pretty straightforward, they will flow where they are allowed, or asked, or forced to.

 

Yes, I am talking about a QV. If I understand what you are saying I agree the second hose seems pointless if there is no temperature sensor at the expansion tank. Maybe a little dentists mirror will shed some light on what goes on inside the expansion tank.

 

The US spec injected engines have the temperature sensing auxiliary air valve mounted to the bottom of the coolant tank. So YES coolant flow thru the tank is required for it to sense coolant temp.

I think I remember reading the engines with lambda feedback may have an additional temp sensor mounted to the tank, but can't directly confirm this.

I've been scratching my head over this question, only thing I've come up with would be to have a radiator shop open the tank up.

 

I had my tank off when I was re-doing the water pump. I sealed and repainted the tank and I did not see any tube inside of my tank. I have no idea if there was one there to begin with or not though.

 

Why not suck on the pipe with a My-T-Vac or similar vacuum? Just like bleeding brakes. Filll the expansion tank, attach a clear hose and suck. If you get just water until the pipe bottom is exposed then I'd say there's no breech. If you get water and bubbles, then I'd say you've got a small hole in the tube. Would this work?

 

Examination with a dentists mirror reveals that the tube that the upper hose connects to on my 1985 QV ends just inside the tank there is no extension at all. I have no reason to believe that it has been altered. One thing that may have been altered is the length of the hose between the coolant manifold and the upper connection to the expansion tank. I replaced all the coolant hoses last year. Is is possible that the original hose had some additional length that would form an important "low spot" or "high spot" that I failed to recreate when I replaced the hose. I am grabbing at straws because I can't actually imagine how that would help.

 

Brian,
It's worth trying.
I'd thought of that & wasn't comfortable reccommending it w/o trying it.
I can't see why it wouldn't work. You'd get some initial bubbles due to air trapped in the hose & tube, but once you got flow going there shouldn't be any more.

GeoMetry,
That's really interesting, I remember some posts a few years ago of pictures of a tank opened up for repair because the internal tube was badly corroded, and another where the tube had corroded enough to come off.

Just tried to get a look inside my '82 QV's tank but the only mirror I have that'll fit thru the hole has a long stem between the mirror & the flex joint so the mirror's out of sight when tilted at the correct angle(sigh).

 

Relatively simple way to check for the existence of an internal tube is to disconnect the upper hose and gently insert something long and thin like a piece of a wire coat hanger. If it goes in far enough that you can see it through the opening on top then there is no internal tube. I would love to see the picture Verell saw because at this point I am skeptical about the existence of this internal tube. I am starting to think it is something we imagine should be there and we see a few threads where they talk about it and then it just becomes accepted.

Please prove me wrong.
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