Sarge Posted August 4, 2009 Share Posted August 4, 2009 A mechanic told me today to never top off my fuel tank in my car/truck beyond the auto shutoff because it will put raw gasoline into the vapor canister and cause major problems with the engine performance. I never heard this before. Thoughts? I have been cramming gas into my tank beyond full for 30 years. Thanks Link to comment Share on other sites More sharing options...
Tiny Warrior Posted August 4, 2009 Share Posted August 4, 2009 I have never heard of that. I fill it with as much as I can most times also. Link to comment Share on other sites More sharing options...
get2now Posted August 4, 2009 Share Posted August 4, 2009 A mechanic told me today to never top off my fuel tank in my car/truck beyond the auto shutoff because it will put raw gasoline into the vapor canister and cause major problems with the engine performance. I never heard this before. Thoughts? I have been cramming gas into my tank beyond full for 30 years.Thanks I heard this a few years ago too. Don't know if it's true or not but now I don't fill it all the way. Just let it stop on it's own and add a little to even the charges. Gary Link to comment Share on other sites More sharing options...
TM262 Posted August 4, 2009 Share Posted August 4, 2009 If I top off my Toyota 4-Runner, it will cause the check engine light to come on. Never knew why, maybe it is true. Link to comment Share on other sites More sharing options...
Sarge Posted August 4, 2009 Author Share Posted August 4, 2009 If I top off my Toyota 4-Runner, it will cause the check engine light to come on. Never knew why, maybe it is true.Could be. He said the fuel will fill up the vapor recovery line to the charcoal canister or something like that. Maybe it IS true. Link to comment Share on other sites More sharing options...
halogrinder Posted August 4, 2009 Share Posted August 4, 2009 'tis true. dont do it. ALSO dont refill while running. Link to comment Share on other sites More sharing options...
scirocco38s Posted August 5, 2009 Share Posted August 5, 2009 on some cars youwill get a check engine light if you dont tighten the gas cap good. I have seen it happen on several GM cars and my brothers truck the other day. He came in complaining his 2 yr old truck was already having problems and he told me engine light was on, I told him to check his cap and 30 minutes later it went off. I think the gas system get pressurized and then it looks for so much pressure in the tank and when it doesnt see it then it triggers the check engine. Link to comment Share on other sites More sharing options...
Merlin Orr Posted August 5, 2009 Share Posted August 5, 2009 'tis true. dont do it. ALSO dont refill while running. Why on the "while running...?" Link to comment Share on other sites More sharing options...
j1b Posted August 5, 2009 Share Posted August 5, 2009 I never top off. Back in the day I think I used to do it to "round" the number to something that was coin resistant. Nowadays I primarily pay with a card. I could care less about what the amount is. Having heard that toping off is bad in the past (can't recall where) it all just came together. No top off for me! J Link to comment Share on other sites More sharing options...
Chris Keen Posted August 5, 2009 Share Posted August 5, 2009 'tis true. dont do it. ALSO dont refill while running. Why on the "while running...?" Merlin I once filled up with the vehicle running (Dodge cargo van) and the check engine light came on while filling up, and NEVER went away. Link to comment Share on other sites More sharing options...
Dave Gundry Posted August 5, 2009 Share Posted August 5, 2009 It is true. In some cars, it can fill the EVAP lines and the carbon canister, along with the rest of the EVAP system. In all OBD2 cars, the EVAP system is sealed. Some cars use leak detection pumps that pressurize the system. Other cars use engine vacuum to 'negatively' pressurize the system. Purge and vent valves then open and close to vent the fumes from the gas tank into the intake manifold. If the system gets plugged or a leak forms, the check engine light will come on to notify the driver there is a problem. By filling this type of system with liquid while it is meant to carry fumes, you can make the system think there is a problem, even causing permanent damage to components of it. Moral of the story - don't do it. You may get away with it, but it's just not worth the risk. Link to comment Share on other sites More sharing options...
Dave Gundry Posted August 5, 2009 Share Posted August 5, 2009 Also, as to why you should not fill the vehicle while running - when you remove the gas cap - you are making a very large leak in the EVAP system, which can set off the check engine light. On some cars it will not trip the CEL unless the leak is present for a longer period of time, and most cars will turn off the light afterward if the leak is not seen for 2 drive cycles (or a preset length of time). The code will still be stored though, which can help confuse your mechanic when troubleshooting other issues. Link to comment Share on other sites More sharing options...
nwb01 Posted August 5, 2009 Share Posted August 5, 2009 Another reason not to overfill..........EXPANSION !! The temp in the tank can get fairly warm due to ambient temperature. Also, most vehicles have a fuel system that returns fuel to the tank. This fuel is hot and causes the temperature to rise in the tank. The tanks are engineered with a dead volume to allow for this expansion. Link to comment Share on other sites More sharing options...
Miranda Posted August 5, 2009 Share Posted August 5, 2009 ooof please don't fill past the auto-shut-off of the pump. there are three reasons: the engineers of the car decided not to build a fuel system that can deal with fuel in the wrong part of the fuel system. the pump has a vapor recovery system and it will suck up the fuel you paid for. You will leak the extra fuel. sigh... the last one is the real reason, because the EPA does not want the vapors loose in the air..... they are dangerous to your health. miranda Link to comment Share on other sites More sharing options...
nwb01 Posted August 5, 2009 Share Posted August 5, 2009 sigh... the last one is the real reason, because the EPA does not want the vapors loose in the air..... they are dangerous to your health. miranda They are only dangerous to lab rats !!!!!!!! oh......I am one of those EPA lab rats !!! Link to comment Share on other sites More sharing options...
boz1911 Posted August 5, 2009 Share Posted August 5, 2009 We deal with evaporative emmissions related check engine lights every friggin day. Please read and heed Dave Gundry's posts he is spot on. Link to comment Share on other sites More sharing options...
DUKE Posted August 5, 2009 Share Posted August 5, 2009 Good information to know! Link to comment Share on other sites More sharing options...
j1b Posted August 7, 2009 Share Posted August 7, 2009 On the opposite end of the tank . . . I have heard it's bad to run a tank down to the last few drops. Whether I like to admit it or not, I tend to let the tank get pretty low before I refill. I've had some folks tell me that running it much below half a tank is worse for the car than refilling at half a tank. I generally get down to less than a quarter tank before I visit the petro station. Anyone heard of this? Is it legit? If I thought there was impact to my vehicle I might actually start filling up a little sooner. Jack Link to comment Share on other sites More sharing options...
Singlestack Posted August 7, 2009 Share Posted August 7, 2009 You run the risk of sucking up any trash in the bottom of the tank and clogging up your filter. Link to comment Share on other sites More sharing options...
Miranda Posted August 7, 2009 Share Posted August 7, 2009 a lot of fuel injection primary pumps run the fuel through the DC motor that drives the pump. that means if the pump gets fuel and air the motor arc will light the mixture. boom? pre burned fuel clogs the injectors ? miranda Link to comment Share on other sites More sharing options...
G-ManBart Posted August 7, 2009 Share Posted August 7, 2009 You run the risk of sucking up any trash in the bottom of the tank and clogging up your filter. That'll depend on where and what type of fuel pickup the vehicle has and whether it's trash that floats or not. If it doesn't float, and the pickup is on the bottom, it's getting sucked up whether the tank is full or empty. Link to comment Share on other sites More sharing options...
BSeevers Posted August 7, 2009 Share Posted August 7, 2009 The real concern is overheating your fuel pump and burning it up. The gas keeps it cool. Link to comment Share on other sites More sharing options...
Miranda Posted August 7, 2009 Share Posted August 7, 2009 over heating the pump works for me. I still wonder about the residual fuel in the overheating pump... miranda Link to comment Share on other sites More sharing options...
boz1911 Posted August 7, 2009 Share Posted August 7, 2009 The real concern is overheating your fuel pump and burning it up. The gas keeps it cool. Yup, the fuel keeps the pump cool. Intank fuel pump replacement is pricey. Running a car til it's empty is murder on these fuel pumps. It also helps to change your fuel filter (if serviceable) on a regular basis so the pump is not working itself to death trying to pump fuel through a resticted filter. Link to comment Share on other sites More sharing options...
Canuck223 Posted August 7, 2009 Share Posted August 7, 2009 Being the cheap and paranoid fellow I am........................... My local gas station is associated with a large automotive/parts/tools chain. The store has had a reward program for the last 70 years, in the form of store cash coupons. The gas bar also offer the coupons, and include a multiplier coupon in thier weekly flyer. Being a two car family, I fill up one vehicle and three 20L gas cans, using the coupon, and walk away with 2-3 dollars a fill up in store coupons. When the next vehicle needs fuel, I dump as much of the stored gas as possible into the other vehicle, and again fuel up the empty van and the gas cans. In that way, I try to keep 60L on hand for emergencys, and rotate the fuel. However, I confess to being guilty of running too low. Link to comment Share on other sites More sharing options...
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