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  • Writer's pictureJohn Baker

Is Starting Fluid Bad for Gas Engines?

In small doses and used properly, starting fluid can help coax a hard-starting engine to life. But, is starting fluid bad for diesel or two-stroke engines? Also, what is starting fluid? We’ll tackle those questions in this post.

What is starting fluid?

It’s a volatile chemical, typically ether, that’s normally packaged in a pressurized spray can. It’s designed to be sprayed in small amounts into the engine’s air intake to help it start. People often use it in extremely cold weather to help start a stubborn engine. But some people also use it to try to start an engine that turns over but won’t fire.

Warnings against its use

Ask five gearheads or mechanics their opinion on the topic and you might get five different answers.

One mechanic I talked to blamed it for ruining the bearings in a two-stroke outboard motor. Its owner, the story goes, liberally sprayed starting fluid into the intake when the engine wouldn’t start. And sprayed. And sprayed.

Ether is an effective solvent and, in this case, it washed the inside of the engine clean of oil, allowing metal components to contact and eventually seize.

Is starting fluid bad for diesel engines?

Diesel engines, too, can suffer the effects of starting fluid. Their high compression can cause it to ignite too early, effectively causing pre-ignition, which invites all kinds of problems, like catastrophic piston or rod damage. Plus, it has no lubricating properties, so it can hasten piston wear.

With minimal work, you can find all sorts of cautionary tales on the Internet of people blowing up engines after using too much starting fluid.

Starting fluid does work (sometimes)

Given the disdain many harbor toward starting fluid, why would anyone use it?

Because it can be effective in gasoline engines – especially carbureted engines – when used as directed.

For gasoline to combust, it must first be vaporized. The fuel injectors in your car or truck do a great job of completing this task.

In carbureted engines, fuel is vaporized as it’s forced through the tiny openings or nozzles in the carburetor. But carburetors don’t vaporize fuel as effectively as fuel injectors. Plus, gasoline doesn’t vaporize as readily when it’s cold. Anyone who’s started a carbureted car or snowblower on a frigid morning knows this all too well. Plus, an engine requires more gas in the fuel/air mixture at startup, making a cold engine doubly difficult to start and keep running.

Starting fluid, on the other hand, does readily ignite in the cold, helping to start the engine and generate heat to more easily vaporize the fuel.

But a little goes a long way. Operator error is to blame for many of the problems noted here, not the fluid itself.

In short, if you have to use starting fluid, use it sparingly. If a couple short bursts into the intake don’t elicit a cough or two from the engine, emptying the can isn’t going to work, either.

No amount of starting fluid is going to revive an engine with a dirty carburetor. Identify the real problem and get it fixed.

Figure out why you need it in the first place

Instead, find out why the engine won’t start in the first place. There’s likely a bigger problem that needs fixing. (If your lawnmower won’t start, check out this post.)

I was presented with this scenario when my snowblower refused to start. So I reached for a can of starting fluid and gave the intake a shot. She sputtered a few times and quit. I repeated the process a few times with the same result.

Eventually, I took apart and cleaned the carb. She roared to life on the first pull after that.

In my case, emptying the entire can into the engine wouldn’t have done a thing, aside from washing the oil from the cylinder and causing wear. At the very least, it helped me diagnose what the problem was not: lack of spark or bad compression.

The bottom line

Starting fluid can help start a stubborn engine, but follow the directions and use it sparingly. If a little bit doesn’t work, a lot likely won’t, either. If your engine is consistently hard to start, find out why and get the real problem fixed.

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