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So what is the current thought when leaving a car to sit for months on end?
It used to be a full tank, but I seem to remember a few times lately, where it's been posted to be better to have a more empty (or almost empty) tank.?
Is this something that is C7 specific or Vette or car wide? Did I imagine it? Either way, what's the reasoning behind it? Mostly with the newer thought on storing it with an almost empty tank.
StaiBil and a full tank is what I do on my boat, as that is what Mercury recommends. Same on my Jet Ski as that is what Yamaha recommends. My Grand Sport does not get stored for long, but is always parked with a full tank,
One quarter of a tank now. You want to keep the fuel level below the sending unit. Sulfur contamination issue. Thousands of dollars to repair the sending unit. With no gas sloshing around the sending unit there is a chance the sulfur "could" be an issue.
^^^ The possible moisture accumulation which is why a full tank was recommended in the past is much less of an issue in the closed tank C7 system than the chance of sulfur contamination of the resistor portion of the fuel sender in the top of the tank.
A number of posts where the C7 fuel sender was replaced (or in some cases fixed with Techron) because the resistor was coated with sulfur. Current thinking is to leave the tank ~1/4 full to keep it out of the fuel during storage. Note, all fuel contains some sulfur. If you read the benifits of the GM fuel additive mentioned in the C7 Owner’s Manual or Techron one of the top listed is desolving sulfur from fuel senders. That however does not always work.
If the sender needs to be replaced in a C7 the exhaust and rear drive train needs to be dropped to get to the tanks. Recall a poster who was horrified when he saw his drive train on the dealers shop floor!
StaiBil and a full tank is what I do on my boat, as that is what Mercury recommends. Same on my Jet Ski as that is what Yamaha recommends. My Grand Sport does not get stored for long, but is always parked with a full tank,
Yep but boats, Jet Skis and my Street Rod don’t need to have the drive train dropped to get to the fuel tank!
I installed the same type of fuel sender in my Street Rod tank when I built it. It’s also vented to the outside, no carbon canister sealed system. I can drop the rear tank very easy to replace it if needed.
Since it mostly goes to shows and often sits for months I do add Stabil every time I fill the tank. With the small tank that fits the tubbed narrow chassis and the ~10 mpg that 502 cid BB gets that is every time it goes to a car show!
Yep but boats, Jet Skis and my Street Rod don’t need to have the drive train dropped to get to the fuel tank!
I installed the same type of fuel sender in my Street Rod tank when I built it. It’s also vented to the outside, no carbon canister sealed system. I can drop the rear tank very easy to replace it if needed.
Since it mostly goes to shows and often sits for months I do add Stabil every time I fill the tank. With the small tank that fits the tubbed narrow chassis and the ~10 mpg that 502 cid BB gets that is every time it goes to a car show!
Interesting on the fuel sensor on the Stingray and only filling to 1/4 I do not store my car, but it does sit for three weeks on a regular basis, as I work 21 days offshore and then am home 21 days, and rotate like that all year. Wonder if I should only have 1/4 in the car when I park it for 3 weeks instead of full like I always do.
^^
Beause of the posts regarding fuel sender issues in the C7 and the need to “take the car half apart” to drop the tanks, I have been doing some things to help! Although my Grand Sport is my DD, I live 17 miles from town, am semi-retired and my Internet business operates out of the home. Also if going to town with my wife or picking up bulky “stuff” I use her SUV. If it rains or looks like it might why get the Vette dirty so use her SUV as well!
So it often sits for a few days. I have been using Techron periodically as a “preventative!” I use it when I fill up and know the Vette will sit for a few days so the sender resistor will be in contact with the extra cleaning additives. Does that help? Don’t know but can’t hurt.
Yep would be logical to leave the fuel lower if sitting for a month, IMO. Not a chemist but it might be something like “epitaxial” growth I am familiar with in welding! That refers to a silica crystal particle, for example, at the top of a solidified weld just completed attaching to a silica particle in the still molten slag above it. Where the molten slag covers the weld deposit that forms a chemical bond that when both the weld and slag cool to room temperature make the slag difficult to remove!
Perhaps when there is no movement of the gasoline in contact with the resistor, sulfur could diffuse though it and attach itself to the sulfur already on the sender.
Don’t know if that is a possible mechanism but perhaps it is.
With today’s sealed gas tank systems that prevent the escape of vapors, moisture entering the tank can’t be a big issue as it was in the past. Therefore don’t see any risk and a possible benifit of keeping ~1/4 full while parked for any length of time.
Ive been winter storing toy cars for 30 years and have always filled tank and added Stabil. Theory was to keep condensation from rusting steel tank from the inside. Have never replaced a fuel pump or sending unit on a winter-stored car, but this year I have a different plan. Last fuel fill of the year will be Ethanol-free 91, will add a bottle of Stabil, and will run it down below 1/4 tank for storage. Someone on this site quoted a GM engineer that stated sulfur can accumulate on the sending unit resistor if left submerged undisturbed for a long time, so Ill buy that story.
^^^
This was my method last weekend. I always have used the full tank method, but this year ran it down to E before filling up with ethanol free and stabil and running back down to 1/4 tank for storage.
A 1/4 tank of gas means the passenger side tank is empty and the driver's side tank is half full. How far down in the tank does the sensor sit? If it is half way down the tank then you would need to be below a 1/4 tank by some amount. There are a lot of people who don't drive their car all that much even in the driving season and the driver's side tank could easily be full for many weeks at a time before the fuel level in that tank drops below full. I think worrying about sulfur deposits is sort of like worrying about your shoe laces being dirty.
A 1/4 tank of gas means the passenger side tank is empty and the driver's side tank is half full. How far down in the tank does the sensor sit? If it is half way down the tank then you would need to be below a 1/4 tank by some amount. There are a lot of people who don't drive their car all that much even in the driving season and the driver's side tank could easily be full for many weeks at a time before the fuel level in that tank drops below full. I think worrying about sulfur deposits is sort of like worrying about your shoe laces being dirty.
Bill
My understanding from Paul Koerner, respected Corvette mechanic, is that if you fill to 1/4 on the gauge, that will adequately prevent the sending unit submerging into the fuel itself and will be left high and dry.
In any event Paul indicated that if the car is stored for "months". His thought is why risk paying for a sending unit replacement when it can easily be prevented. I guess that if we have the information we can use according to what we are comfortable with doing. All I can say if he would do this with a stored C7 I will follow suit. I'm absolutely positive you know more than I do on this subject Bill. I'm just going by what Paul stated.
Last edited by joemessman; 11-07-2018 at 03:52 PM.
My understanding from Paul Koerner, respected Corvette mechanic, is that if you fill to 1/4 on the gauge, that will adequately prevent the sending unit submerging into the fuel itself and will be left high and dry.
In any event Paul indicated that if the car is stored for "months". His thought is why risk paying for a sending unit replacement when it can easily be prevented. I guess that if we have the information we can use according to what we are comfortable with doing. All I can say if he would do this with a stored C7 I will follow suit. I'm absolutely positive you know more than I do on this subject Bill. I'm just going by what Paul stated.
Correct, Paul services my C7 and always states in his seminars that GM recommends 1/4 or less fuel in the car when storing. The cost of dropping the drive train and replacing the sensor is very expensive, also with the tanks being made of plastic there is less of a chance for condensation. On my last tank of gas I treat with Stabil and Techron and run it down. I have done it this way now for three years with no problem.
A 1/4 tank of gas means the passenger side tank is empty and the driver's side tank is half full. How far down in the tank does the sensor sit? If it is half way down the tank then you would need to be below a 1/4 tank by some amount.
Bill
Looking at the sketch in the service manual the resistor is near the flange that bolts to the tank top. Note the text in the Service Manual says when removed there is a spring that separates the pieces, which is why I think it looks further down from the top flange in the sketch in post #6.. Therefore if it's half way down in that tank, the resistor that can get contaminated would be out of the gas.
A number of Forum posts where the sensor failed. Some solve with Techron or GM fuel cleaner- but no guarantee that will work.
On warranty, dealer is sure to opt for the max GM compensation and the ~day’s time to drop the exhaust and rear parts of drive train to drop the tank1. I prefer a $5 Techron occationally on chance it will help to the Chevy dealer putting it all back correctly.
If you read the top few benifits listed for Techron and the GM fuel cleaning additive (SDS are very similar) removing sulfur from fuel senders is listed. Not an uncommon problem but in the C7 just hard to replace.
11-06-2018, 11:20 PM
Fuel level when Winterizing
The possible moisture accumulation which is why a full tank was recommended in the past is much less of an issue in the closed tank C7 system than the chance of sulfur contamination of the resistor portion of the fuel sender in the top of the tank.
