Engine cleaner instructions: by chemists or lawyers?

I need to clean an engine - gonna use some spray-on stuff (Gunk). Instructions say to use only when the engine is cold. Who wrote this, lawyers or chemists? I need to do this on a warm engine, but obviously not if there's a real chance that the car and I will go up in a ball of flames. 

Find out for yourself. Take an old frying pan, heat it up, spray gunk on. Flames? No? You good. Yes flames? Bad. 

Most of the time that stuff isn't flammable, but rather, it's caustic with steamed or smoked. 

I've yet to blow anything up spraying it on a warm engine.  It did rinse all the gunk off the heads of the wrx onto the cats and make about 20 miles of fogging for insects after use.

probably more worried about fumes affecting you

Super Clean and a toilet brush smashed into an appropriate shape.

mad_machine said:

probably more worried about fumes affecting you

 

This. 

So, Lawyers. 

IIRC, there was a brand years ago that specifically recommend application to a hot engine. 

I imagine there is a distinct possibility of cracking hot cast exhaust manifolds by spraying cold engine cleaner on them too. 

I'm thinking it's to keep from hurting the exhaust manifolds and cats.  

I'm a chemist at a consumer products company, and I write those instructions. Actually, one of the biggest things I learned when I came into the industry is that you really should read and follow the directions on most stuff because there's a good chance that the directions were developed as the most effective, safest way to use the product. That doesn't mean that corporate liability doesn't come into play of course.

I can't say for sure on your product without seeing an SDS or a formula for it, but there are several things that might drive that "cold engine" recommendation. Flammability is obviously the primary one, particularly if it's an aerosol that uses flammable propellant. Secondly is your respiratory health. Many heavy grease cutters use caustic soda and aggressive surfactants that will play hell on your lungs if you inhale the vapors - and that's 1000 times worse on a hot surface. Another thought is that some of these same chemicals can be really rough on plastics and wiring insulation at elevated temps. 

Now from a  liability position - how many customers won't know the difference between "warm" and "glowing red hot?"  If you spray a cold liquid on a red hot block or manifold and it cracks, who gets to pay the legal bill? Use instructions are certainly written to avoid even glancing in the direction of something that could cause problems - as much protecting some customers from themselves as protecting the company many times.

If it were me, I'd use it exactly by directions first and then adjust if it doesn't work. A little warmth will help soften heavy grease a lot, but be more careful around plastics than normal and know that if you berk something up, it's on you.

Ugh so the REply and Quote buttons won't work consistently for me so have to do this manually.

REPLY to Ultraclyde:

I second Ultraclyde's comments. I also worked in the consumer products and the auto industry. I found it interesting when we engineers spent months or years figuring something out. Dealing with reversing dreadful supplier "improvements" that turned our products into poisonous scrap.  (follow the berkeleying print!!!) Going over multiple painful edits of the instruction/warning/advertising language and then have one of my family members try to get me to "confess" it is all just CYA.

If you have the proper downdraft ventilation with sufficient air replacement, plus a proper filtered full face mask and suit you can spray that engine cleaner on whatever temp engine you want. But if you don't have that equipment and don't want to inhale stuff that will, WILL, degrade your health then follow the instructions. If I was going to use engine cleaner at the local DIY car wash I would park back from the bay out of the way, let the car cool, then push the car into the bay.  I did that several times or just go when it is raining and there won't be any grumpy people. 

https://www.youtube.com/embed/akgS7TA-4vs?start=119

This thread reminded me of this scene. "If you use an areosol can in a manner other than directed,.....I will put you away."

The gunk brand isnt good on the lungs spraying it on a hot engine. I learned it the hard way.