I've had an occasional leak with a full tank, but of course it always occurred when I did not have the opportunity to trace it. It usually occurse overnight, and not during the day, which seems odd to me. anything less than 3/4 tank, and there are no leaks.

This morning after filling up yestrday morning I smelled fuel and had time, and finally found the source at the fuel pump. The top of the pump is saturated, as is the depression in the tank where the fuel has leaked out. Needless to say I'd like to fix it ASAP, and am wondering if this is a common problem...and if so, is it most likely to be the pump to tank seal, or the pump itself?

My fuel tank is still leaking at the fuel pump. In case teh original message does not post with this, the only time it leaks is on a full tank, and at night, when you'd expect the cool weather to cause fuelk to contract, not expand. I did locate teh source as being in the immediate vicinity of the fuel pump, in fact the top of the pum is covered with gas when this happens. A new pump to tank seal did not correct this, and the orings inside the fuel line connectors appear to be OK, but are hard to see.

Any ideas where to look next? teh fuel line seals or could it be the pump istself? (Oh, and Klaus, the purge check valve seems to be functioning, but how is one sure?)

Your real problem may be the check valve by the charcoal cannister. There is too much pressure in the tank and the cannister is not being purged when the engine is running????? Or the return line could be cracked, but then you would have gasoline there after you run the car.

I use the handles from a pair of conventional pliers to get the cap off.

Klaus
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Please answer your responses. We need to know if the advice is good or bad. The 164 has a new home, all I am left with are 2 turbos :)

I finally had the opportunity to put the new pump seal in. The old one looked fine, no tears, dirt, or kinks. The tank opening seemed fine, and I saw no cracks or damage to the pump. I took the time to check the o-rings in the fuel line connections, and they seemed OK too. So far, no leaks, but time will tell.

The only thing I found that *might* have caused teh leakage is that the return line wasn't fully seated onto the pump. Yet why would it only leak when full, and only overnight when it cools off? Tomorrow I will check the the vapor cannister and purge valve.

The oldest B230s I have are a 91 940SE Turbo and a 92 240, therefore I am not sure what makes an 83 tick, but it cannot be too different. A drop in MPGs could be caused by the O2 sensor as stated and even more so by a bad ECT. Common sense items, check vac hoses, including the charcoal canister hoses. If you don’t have a engine temp sensor, I do remember the canister in my son’s ’78. An engine with poor MPG means your are running rich. Too much un-burnt fuel will eventually clog your cat.

Edit, sorry butch, this responce was meant for H4L.

lol, the post above yours under my name (butch), that you answered by mistake or whatever is not my original post at all. I have no idea what is going on.

I'll have to look into the cannister check valve...where is it located, and do you think this would happen only on a full tank?

The pump seal will be in tomorrow, so that will be the first order of business.

The cannister purge valve is quite expensive. It is closed when the engine is not running and open when the engine is running, allowing the charcoal to release trapped fumes to enter the intake manifold.
Often, the cause of a cannister full of gasoline is the result of over filling the tank, ie. forcing the last drop (.5 gallon) into the filler neck. That raw gasoline enters the line to the cannister and causes tank expansion problems.
Remember, the gasoline you get from the pump is at about 60F. Then when the car sits, the gasoline temp rises to the ambient temp - expanding with ever increasing heat. When the vapors try to expand with no place to go, it is a sealed system, and if the seal to the pump or fuel level cap has a crack, that is where it will go.
Give the new seal a chance and never add more gasoline to round off to the nearest dollar.

Klaus
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Please answer your responses. We need to know if the advice is good or bad. The 164 has a new home, all I am left with are 2 turbos :)

I'm not one to "top off" the tank, except to round it to the nearest $.05, which is about impossible anymore...the pump spins too fast! So hopefuly that valve is not it ( and where is it BTW?). Further more, if I fill in the morning on a warm day, it does not leak all day long...but once night comes and it cools off, here coems the leak. Kind of odd, but that's what it does!

I probably shouldn't break in, but the evap purge valve is mounted to the rear top of the radiator shroud with two torx bolts, right under where the air intake passes over the shround. It has a two wire connector, and two hoses. One goes down and over to the cannister (under the front corner of the left fender). The other hose goes to the intake manifold.

To test quickly test Klaus' theory of the cannister having gas in it, I wonder if you could unmount the cannister (just one bolt), and see how heavy it is? I just had mine off, and noticed how lightweight it is. It literally doesn't seem heavier than the plastic that makes up the cannister.

Just a thought. Good luck. Don

No, jump right in! More advice is welcome.

I got teh gasket, but won't have time to change it tonight. I'll swap it tomorrow and refill the tank, and post the results.

I've never heard of this problem on an 850 before. It must either be the tank seal (big round threaded cap) or the feed or return line. I doubt it's the pressurized fuel lines as they would leak all the time.

The tank cap/nut/seal is all plastic as I recall. So there's not much to rust. I can't remember what actually seals it, but it must be an o-ring in there that was left out by a PO or has somehow degraded.

It couldn't be the connection at the filler neck could it?

Good luck,
-Will
850 / Mini

Nope, not the fuel filler, like I thought at first. The cap holding the pump in place appears to be OK, so sonce it is only when the tank is full, I'm suspecting it's the seal. BY luck, our region's Volvo Dealer just moved their place pretty close to home, so I stopped by and ordered one. I'll report what I find.