Cracked Block Probability

I think you are very unlikely to crack a block by pouring cold water on a hot block. The blocks just are not that hot. Think about this - Cast iron exhaust headers are much hotter than the blcok ever will be. Yet, how often are they cracked when you drive through a deep puddle and splash water all over the exhaust manifold?

Ed

Williams wrote:

Perhaps if you have an engine that is totally devoid of water and is in an engine damaging state of overheat perhaps you could damage the engine by adding near frozen water to the radiator.

Biggest risk in attempting to add water to a hot engine is steam burns when you open the radiator cap... since pretty much all current engines run with pressurized systems.

If an engine is overheated, best way to add water is to first pour it onto the radiator core to cool that down, ideally with the engine running. If that works, run the engine a while to cool off any hot spots, then shut the engine down and allow it to cool so the radiator can be safely opened.

Then add water only in an emergency, as the engine would really prefer a good drink of antifreeze/water mix.

If you do add water [or even mixed antifreeze] it won't hurt anything to do it with the engine running, may even help get rid of water bubbles. However it takes a while as when the water is colder than the thermostat temperature, the thermostat will close and pretty much stop circulation of the water from the radiator until the temp goes high enough to open the 'stat again. With the cap off you can make sure water is circulating properly, look for air bubbles, etc. as you refill. Then put the cap on and make sure the overflow bottle is clean and full as thats where some engines have a coolant level warning sensor.

I suppose if there were a defective casting, the thermal shock of really cold water in a hot engine could damage it... if it gets much cold water into the engine before the thermostat closes.

Thanks for the sensible reply Lon. You make it sound like an urban myth, so where are all these people who supposedly crack their blocks, I'm hoping to hear from them.

Apparently, one of the durability tests GM did on their new Ecotec 2.2L engine was a thermal cycle test, where they ran the engine up to normal operating temperature and then flushed it with ice-cold coolant. The engine was required to survive this being repeated continuously for 1000 hours.

So, I would say the chances of most engines being damaged from this are pretty low..

I have an older Chev pickup. It developed a leak and ran completely dry while driving it. I removed the radiator cap with a towel over it and there was no steam at all. I let it set for about 5 minutes and then tried adding water into the radiator. It immediately turned to a huge amount of steam and blew super hot water back onto my arm. (lucky I had a jacket on). The point being that care taken when opening the radiator cap should also extend to the refilling process.

Bob

Thanks for the replies. Is not even one person going to tell of a cracked block? Is it just an urban myth?

Not everyone that's ever poured cold water into a hot engine reads this newsgroup, or even has internet access for that matter. The internet's big, but it's not that big.

The concensus is that it's a bad idea, but you need to decide for yourself whether you agree or not.

JazzMan

I don't think anyone is saying that it couldn't happen, just that nobody has had it happen to them, their acquaintances, etc. etc. and further that it is bloody freaking unlikely under reasonable circumstances. Granted, some folks shouldn't be allowed near anything mechanical, which is why it is possible it could have happened.

I'd avoid adding water until the motor drops to operating tempurature, with engine off. If it's enough to crack the block then the head is probably first to go.

To the OP: The only scenarios I seen with crack blocks are from trapped coolant under the head bolts, connecting rods failure and adding extremely cold water to an overheated block.

Tibur

Some blocks are easier to crack than others. (Some of them did it naturally, with no abusive treatment.)

Often, if you overheat an engine moderately, especially one with aluminum block or heads, you may find you have warpage. It is more common for the head to warp, but not impossible for the block to do it too.

You won't get enough steam pressure to crack a block, but you can crack them with shock.

Normally, if you haven't driven the vehicle into the depths of Hell, you can play water over the radiator, with the engine running, and get a bit of cooling...maybe enough to get it under control with little damage. You must NOT run up and open the radiator cap on a car like this, unless you really didn't value that hand anyway.

If you have destroyed the main bearings, say goodnight Gracie. You might as well shut it off and let it cool naturally. It will need to see the engine doctor.

My uncle (may he rest in peace) used to tell me stories about borrowing a family member's Model T, and running it out of water. He said that the block was glowing red hot when he realized what he had done (literary license or truth, I don't know). He said he got a bucket of water out of the river and drowned that engine with it. The block didn't crack. (I believe in those days Babbitt metal bearings were used, and if so, a red hot condition would have certainly melted the Babbitt). Cranked it up and drove off.

He was a fun guy, and his pictures had been taken off the post office bulletin boards when I heard this story.

Bottom line... If you get yourself in this condition, you have to determine quickly whether to try to cool the radiator or shut her off. Above all, be safe.

Takes me back...

Four months pregnant and one of mine blew. Yeah, like we need those in SoCal. For a while I could use the car by filling it up at home, driving to work, filling it up at work and driving home. Ultimately I crawled under the 1950 Chevy and replaced the STEEL freeze plug with a brass one. Fortunately only one went bad.

It would have killed GM to use brass in the first place? Do they still use them at all?

Yep, pretty much every engine still has core plugs in the block and head(s). The only easy way to get the sand out of the water jacket areas. The ones that don't have them are normally engines that use wet sleeves like diesels and large engines that have hatches into the block.

I am informed that SOME cars have plugs at the other end of the block such that you have to lift the engine to replace them. How evil is that?

For extremely difficult and time-consuming values of 'easy'. Where does the sand come from and what does it do? We've been driving old cars (1968-70) for a long time and if we have sand we sure don't know it!

The block is sandcast, then some stuff on it is precision machined. It is not just machined out of a solid billet. When you pop off the head cover, you can see the rough surfaces that result from unfinished sand casting.

And when you sandcast, you have to get all the sand out because it is abrasive. Even with pretty aggressive removal, there's usually still some left that comes out during the break-in process.

--scott

This is a good video on engine block mfg:

It looks like Goggle/youtube has found a way past all my ad blockers and user agents. Hit Refresh one or more times to get past the ads.

Yep, pointless in SoCal but significant up nort'.

They're a necessary foible of the sandcasting process (my GM aluminum engine doesn't have them) and do indeed prevent total block loss if the operator neglects coolant mixture in severe cold. I'm not at all sure that brass or steel plugs would function or fail differently.

I have worked on very large engines that have screwed in brass casting plugs. They generally don't fail in terms of leakage or corrosion but cost a lot more in the manufacturing process. They also won't conveniently pop out in the case of the coolant freezing.

In general however, the standard variety welch plugs come in two forms, dished and domed. They are made of plated steel but can be had in brass at a higher cost. Use an appropriate coolant and the factory OEM units should last out the engine at least until rebuild time where it would be prudent to replace them.