Engine Damage from Block Heaters?

Ok Gang, I think I already know the answer to this one, but I feel I should still post it to see if anyone knows why this particular rumour/myth came into being:

I was talking to a co-worker about the use of a block heater for my 2002 Hyundai Accent when the temperature was down to -35 this past week (celcius that is…)
He claims that using a block heater can “damage the metal of your engine” and make the car “start to need it more and more, even in temperatures where it didn’t before”

I asked him how the engine can differentiate between the heat that the heater produces, and that which the engine produces, but I didn’t get much of an answer. It was then that I dismissed the arguments as misguided.

So, I bring this to you all in the hopes that this can be resolved.

Where did the idea of damage to the engine and the unnecessary need in warmer temperatures arise?

I really, really doubt this.

It’s much better on the engine to start it when it is warm. Oil will circulate better.

I highly doubt this too. An engine block gets far hotter in operation than sitting idle with a block heater. Maybe your mechanic just hopes that the extra wear caused by starting in very cold weather would bring your business to him sooner?

There are different types of block heaters. Some go into the dipstick tube (not recommended) but most are inline with the lower radiator hose. They merely heat the water in the hose and the heat rises naturally into the water jacket around the block. It doesnt dramatically increase the temp of the block itself. It merely makes it "warmer" than the ambient temp. It will also prevent any ice from developing inside the hoses and the radiator. If you were to put your hand on the oil pan you would not feel the difference, meaning that the oil itself would still be cold. I cant explain the myth, except to say that maybe the guys a putz.

Your co-worker does not have a clue and is totally wrong.

I will point out that vehicles and machinery with large engines often have separate, fuel-burning, heaters to heat the engine before it is started. A warm engine starts and runs better. Warming up the engine before starting it is a good thing.

He has absolutely no clue. Pay no attention to him.

Actually, most go in place of a frost plug on the engine block.
I haven’t seen a dipstick tube heater in years, but I suspect they’re still out there. But yes, you’re correct, there are different types.

The only real damage that block heaters cause is to the oil. Modern oils have additives that coat the internal metal parts of the engine. These additives will break down quicker if the oil is kept warm. If you change your oil at the recommended intervals, it should not cause any problems.

I second this comment, verbatim.

Jimminy Cricket, Racer, what kind of heater are you using? We’re not talking about an acetylene torch here (at least, I hope not). A block heater shouldn’t get near as warm as an actual running engine, so I’m not sure that argument holds water. If someone changes the oil so infrequently that this would be a factor I think there are more problems than just cold weather going on.

The block heaters I’m famillar with throw noticable heat, but it’s still cool enough you can comfortably put your hand on any part of the engine without discomfort. Maybe 100-120 degrees F max? (That would be around 42-45 C) I take baths in water that hot.

As for the engine “getting used to it” - I think it’s more the owner gets used to an engine that starts reliably, and starts using it more and more.

Everything I know about engines (and granted, I’m not an expert, I just use 'em on a daily basis) tells me that sub-freezing starts are harder on them than above-freezing starts. The colder it gets, the worse the problem.

The newer cars seem to do alright down to -20 F, which if I figure right isn’t too far from the OP’s -35 C, but if you get a LOT of that fridgid cold maybe a engine block warmer isn’t a bad investment. My area can get that cold, but it doesn’t stay that cold for weeks on end. As always, YMMV

On some newer all aluminum engines the block heater is designed to clamp onto the the block webbing and does not go into a freeze plug since the block doesn’t have any of these.

With this type of heater there is a slight risk, **if the heater is not installed correctly, ** of damage to the block at the installation site. This is not a function of the heater, per se, but rather of the dimwitted installer.

I do not expect you friend was aware of this. I think, as other have stated, that he is without a clue.

This reminds me of the warning I got that garaging my car would make it rust faster. Well, my neighbour and I bought twin Honda Civic wagons in 1990 (the last year they were sold here). He leaves his out all winter, while I put mine in the garage between November and April. His kind of decayed away and he junked it last summer and mine is still going strong with a few spots of rust, but nothing serious. I would put this in the category of an urban myth.

*He claims that using a block heater can “damage the metal of your engine” and make the car “start to need it more and more, even in temperatures where it didn’t before”

Where did the idea of damage to the engine and the unnecessary need in warmer temperatures arise?*

I dunno where the heck he got those ideas, or how anyone would come up with them, but I agree that it’s utter nonsense.

i’ll go with putz.

This is very similar to the caution you will hear from many mechanics relating to using ether (starting fluid) on a cold diesel engine, Stupendous man.
Perhaps your co-worker has heard this and somehow distorted or mis-remembered it? :
If the engine doesn’t fire almost immediately the ether can quickly dry the film of oil between the rings and sleeves and can “damage the metal of your engine”. This will lead to some loss of compression (blow-by) and since a diesel uses compression to ignite its fuel it may “start to need it more and more, even in temperatures where it didn’t before”. Meaning that with the slight loss of compression caused by previous usage of ether, the engine will now be even more difficult to start when cold, and will need the ether’s volatiity to reduce the compression required to start it, and so on.

Block “heaters” are like any other mood enhancers. Sure, at first your engine uses it just a bit, just to get going in the morning. They think they can quit any time. But then it starts to creep up on them. They start wanting that warm cozy feeling all the time, not just in the morning, and they’ll start going to any lengths to get it. The worst cases are the ones that you see “plugged in” outside the garages in the summer time. Even though they’re in for re-conditioning, to break the habit, they still need it when it’s +30 C.

It’s all very sad, really, and with all the cut-backs to the Canadian Autocare system, I think the problem will just keep getting worse. The only bright ray of hope is that with global warming, fewer young cars will need the “heater” in the first place.

How can I get my car to break this vicious cycle?

Well, thanks everyone for those answers. I suspected as much.


I’ve been using various heaters for over 20 years.

I currently have one of the variety that mounts in one of the freeze plug holes. It’s on at the moment, BTW. I have one of the X-10 remote control modules to turn it on and off, and a computer connected to an outdoor thermometer that sends a signal to turn it on when the temperature drops below 15F.

I also have a magnetic stick-on heater on my generator, also connected to an X-10 module.

I’ve tried most of the others. They all have similar results. The engine stays warm enough so the oil is fluid enough to crank the engine, but not exactly warm to the touch. The variety that goes in the radiator hose seems to keep the engine warmest, to the point that the heater may put out a small amount of heat (very small) when the engine is first started.

The variety that goes in the oil is the worst choice. To get all the oil a little warm, the oil in contact with the heater must get hot. All oil breaks down over time, and the hotter it gets the less time it takes. However, oil in a running engine gets pretty hot anyway, and cranking a cold engine is really hard on the battery and starter. Pick your poison.

Personally, I think your friend is just trying to justify the fact that he doesn’t have one.