Harmful to top off a Diesel fuel tank?

[Midnight Rider]

I have a Chevy 3500 HD and I was wondering if it is bad to top off the tank when filling?
Thoughts?
Thanks
MR

 

[1911LVR]

I never top off my tank. Fuel needs head space.

 

[BryanValRox]

I have a Chevy 3500 HD and I was wondering if it is bad to top off the tank when filling?
Thoughts?
Thanks
MR

Well, as 1911LVR has stated the fuel does need some head(expansion)space for temperature changes.
Top off normally wouldn’t hurt anything mechanically but things could get messy if you top it off and let her sit on a hot day.
Also if you do get overzealous at the pump, @ 10 miles later you will have your expansion space back🤣.
I normally just stop when the pump cuts off.

 

[M and E]

I have a Chevy 3500 HD and I was wondering if it is bad to top off the tank when filling?
Thoughts?
Thanks
MR

No; it is not harmful to top off a fuel tank in modern diesel engines. In hot weather, and if you are going to park it immediately after filling, there is a risk of expansion and overflow.

 

[Bozo]

I let her kick off, wait 5 seconds and finish topping off. If you do more than once, splash back will occur, especially on a real truck pump.

 

[Midnight Rider]

Thanks for the responses!
I just do it to get as much fuel in it to go farther between stops. I never fill and let it sit.
i read somewhere that on a gas engine it can create harmful suction on the system if the gas cap is to tight?

 

[Bozo]

Thanks for the responses!
I just do it to get as much fuel in it to go farther between stops. I never fill and let it sit.
i read somewhere that on a gas engine it can create harmful suction on the system if the gas cap is to tight?

I definitely do that on fuel stops when traveling.

 

[M and E]

Thanks for the responses!
I just do it to get as much fuel in it to go farther between stops. I never fill and let it sit.
i read somewhere that on a gas engine it can create harmful suction on the system if the gas cap is to tight?

Not really. There are two types of systems, vented and sealed. If the cap fails on a vented system then there is a risk of tank deformation, seal failures, etc. On a sealed system the cap needs to be tight. You might have seen people who get a check engine light and al they needed to do was tighten the gas cap a click or two more; those are typically sealed systems and the fuel monitoring system detected improper pressures because air was entering the system. In either case, and it is not uncommon, the evap system, which captures fuel vapors that are sent to the cylinders for combustion, can be damaged by overfilling.

 

[Midnight Rider]

Not really. There are two types of systems, vented and sealed. If the cap fails on a vented system then there is a risk of tank deformation, seal failures, etc. On a sealed system the cap needs to be tight. You might have seen people who get a check engine light and al they needed to do was tighten the gas cap a click or two more; those are typically sealed systems and the fuel monitoring system detected improper pressures because air was entering the system. In either case, and it is not uncommon, the evap system, which captures fuel vapors that are sent to the cylinders for combustion, can be damaged by overfilling.

So no harm on topping of the 2024 Chevy 3500 HD Diesel?

 

[M and E]

So no harm on topping of the 2024 Chevy 3500 HD Diesel?

Nope, no risk of harm. GM, Ford, and Ram (Stellantis) will confirm this for you via email or phone. But the only benefit it provides is a bit of range (unless you are trying to get proper mixing ratio of something like Extreme Clean). Diesel tanks are vented and there is not a charcoal cannister on an evap system like there are in gas engines.

 

[JWalker]

We have our auxiliary tank connected to the filler neck about 8 inches from the cap. So it will fill to that point almost all the time. And we’ve never had an issue.