Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Water in gas?

Hey, guys. I just got back to town with my Supra, 298,000 mi, 7M-GE 3.0L engine. I think I picked up some bad gas on the road. It’s acting like I’ve got dome water in the tank. I’ve already run a couple of tankfuls. I know the proper way to fix this is to drop the tank and clean it out. But, I can’t do that until this weekend, maybe. It’s been a couple of decades since I dealt with this. What can I add to the gas to help get rid of some of it until I can drop the tank?

If it’s water, you don’t have to drop the tank. Add some isopropanol (isopropyl alchohol), sold
commonly as Iso-Heet. This alchohol will sink to the bottom of the tank, mix with the water,
and allow you to burn it out. If the problem is bad, you might want to add more than one little
bottle per tank, and do it for more than one tank.

Christy DryGas Was, I believe, The Original Commercial Product Intended To Aid With Water In Gasoline Problems.

Christy DryGas is also still on the market and sold in many locations. I believe many of these products, sold under different brands, have similar ingredients and will do the job. Christy trade marked the name Dry-Gas, so other companies have to be creative with names for their “gas driers”.


Where do you live? What makes you think there’s water in the tank. Water in gas has been an impossibility here in Washington for many years because of the ethanol requirements. Was the suspected gas you bought ethanol-free?

Possible, but I would suspect something else at close to 300k miles.

If bad gas is a supect the best thing to do is siphon,drain, or run a sample out into a clear container. Any contaminants or water will settle in the bottom of the container just like they will in the gas tank.

Melott stole the words right out of my mouth. Another way you can confirm if you do indeed have water in your fuel would be to pull off the fuel line from the injector rail and pump some fuel into a glass jar. See if you have any separation. If you do…then alcohol will help you remove it.


Bad gas gets blamed for far, far more problems than it actually causes. I too wonder why you suspect water in the gas and if you’ve checked for anything else.

By the way, what year is your Supra?

According to what I’ve read, ethanol in gas tends to make the water problem worse, not better.
I don’t fully understand this, but allegedly this increases the tendency to separate into a water-alcohol layer and a gas-alcohol layer (on top). Supposedly isopropanol helps to mix this up so that the whole thing can be removed slowly. Supposedly much worse on old-time vented gas tanks.

According to what I've read, ethanol in gas tends to make the water problem worse, not better.

Definitely makes it better.

@melott , thanks a bunch. It’s been forever since I’ve had to deal with this problem and couldn’t remember the name. The car is an '88 model, so it has a vacuum/mechanical evap system and a sealed tank. I know I got a bad batch of fuel. The car ran crappy almost as soon as I got the stuff. As soon as I got it down to half a tank, I loaded it up with premium and the car ran better. Next tank, I added a bottle of Techron, thinking the crappy stuff may have fouled the injectors. The car would start up rough in the morning, but clear up If you revved it. Once clear, you’d have a momentary hiccup, like a full-on misfire maybe once a minute or longer. Pulling a fuel line on this car is not easy. But, I just put a bottle of Iso-Heet and a full tank of premium in it. I’m almost certain there is water sitting just below the fuel pick-up thanks to that crappy load of gas. We’ll see how it goes. $3.99 for the Iso-Heet and $2.25 extra for premium over mid-grade sure beats pulling a fuel line or dropping the tank.

I think there are some other brands that are a lot cheaper than Isoheet. I think I got some at O’Reillys. And I hear some pharmacies sell isopropanol, but you have to be careful not to get rubbing alcohol with 30% water in it.
Let us know if this helps. I would recommend running the tank down to below 1/4 full before you fill it and put in another slug of isopropanol.

Not all premium is ethanol-free. It is hard to find ethanol-free gas.

“Not all premium is ethanol-free. It is hard to find ethanol-free gas.”

I have at least two stations near where I live that sell REC90, ethanol-free gas, intended for off-road use. That’s what I put in cans for small engines, boats, etcetera.


Using premium gains you nothing unless your engine requires it. A waste of money. You can get 90% isopropanol at any drug store.

Why would you want ethanol free? From what I understand, the alcohol (ethanol or isopropanol) mixes with any water present and allows it to be burned.


Ethanol absorbs water. With only a little bit of water it will phase separate from the gas and go to the bottom of your gas tank and sit there. Isopropanol has a much lower tendency to phase separate. Thus it may somewhat more cheaply help get the water out of your gas tank.

I agree with the comment that premium is unnecessary–except that it is a little bit more likely to be ethanol free, at some stations. A list of such stations–including some with ethanol-free regular is available at
but it is a bit out of date.

I would not buy the 90% isopropanol at a pharmacy. It is 10% water, and you don’t want to be adding water. However, I think some places have 99% isopropanol.

Ethanol free gas is very dependent on where you live. You can’t buy it in Southern NH or Eastern MA. State law prohibits gas stations from selling ethanol free gas in those areas.

“some pharmacies sell isopropanol, but you have to be careful not to get rubbing alcohol with 30% water in it.”

Actually, all pharmacies sell isopropanol, but most of it is the aforementioned 70% iso/30% water.
If you look carefully, you may find 91% isopropanol, but that product is still 9% water.

I have never seen 100% isopropanol sold in a pharmacy.

My car originally called for 91 octane. Some experimentation on my high-mileage engine showed that mid-grade was fine for general traffic. However, I still use premium when I do extended high-speed driving and performance driving. I added the Iso-Heet with my gas needle right near empty. I have a 16 gal tank with a 3/4 gal reserve (at least as far as I’ve dared to test it), and it took 15.35 gal to the first click. At $3.99 for the Iso-Heet, I’m not going to quibble over a buck or two savings. Plus, I live in Atlanta. There are no close stations selling ethanol-free, since we are a smog-alert area with emissions testing. The closest station I found is 30 miles north out of the smog zone. I could go 15 miles North and get 100 octane ethanol-free race fuel in Commerce, Ga for $10/gal at the pump, but that right there is overkill.

you can buy “lab-grade” isopropanol which is close to 100%. but it is expensive, and once you open the bottle, it absorbs water from the air and quickly becomes diluted. the 91% is about as good as you can get. It is still capable of absorbing lots of water.

Again, ethanol in gasoline is a help in absorbing water, not a hinderance.


Here in FL ethanol free gas is appearing more and more…My 89 Mustang GT calls for 87 but the lowest octane I can get for ethanol free is 89. I only use this fuel as my stang was not meant to run on ethanol based fuel, but it ran without problems for a few years…If gas has ethanol in it I pass…Non ethanol also good for lawn yard equipment. I went through 2 weed eater carb problems using ethanol based fuel. On my gas chain saw, the ethanol free gas attacked the gas tank cap. It seemed to swell the cap and could not loosen it.