Heater core? What?

December 2, 2008 3:53 PM

The mechanic said my heater core needs to be replaced and it will cost $700. What does this mean? Lengthy explanation inside.

Background: I bought my 1995 Toyota Corrolla this last summer. Got it checked out by a reputable mechanic (Mechanic A) who found no major problems.

I've only ever had one problem - one day about a month ago, I was driving it on a city street. I was stopped at a red light and when the light turned green and I pressed down on the gas, the car stalled out, luckily right next to a gas station. I was able to to steer the car into the gas station, where, after letting it sit for a minute, it started up again with no problem. I'm not sure if this is relevant to my current issue.

Once winter rolled around, I realized the heat didn't work - it would blow, but blow cold. So last Monday I took it to a mechanic recommended by a friend (Mechanic B) who changed the thermostat and cleaned out the heater core, which he said was clogged but didn't seem to think had been a big problem. After this, the heater worked perfectly.

I barely drove the car for a week after getting the heater fixed because I was home for Thanksgiving. I drove it yesterday with no problem, but today when I was driving it I noticed that a white steam had started to billow up from under the hood.

I took it to a mechanic - the steam had stopped at this point - near my house (Mechanic C) who told me that there was no antifreeze and that the heater core was ruined.

Here's where it gets a little confusing. He was not really able to explain very well what was wrong with the heater core or why it would cost $700 to replace. He says without a working heater core, the engine could overheat. He did say I should be able to drive it for a day or so without incident, so I drove it home and I'm planning to take it back to back to Mechanic A tomorrow for a second opinion.

However, before I take it to a mechanic, I'd like to have an idea of what's going on, since it sort of felt like Mechanic C was trying to scam me. I've been poking around on the internet and read these questions, but I have to say I still don't really understand what's going on here. Why would this repair cost so much? Will a failed heater core really ruin my car? If my heater core is still all clogged, why has the heat been working so well in my car? And am I safe to drive the car to the mechanic (4 miles away) tomorrow? (I drove it home with no trouble)

Thanks in advance for helping out a car-illiterate mefite!

posted by lunasol to travel & transportation (18 comments total)

Your heater core may have a leak (antifreeze leaking onto hot engine parts could cause the white smoke). If it does, it needs to be replaced. Pulling it out is most likely a pain to do, and so there's a lot of labor involved. The part itself probably isn't cheap either. $700 doesn't sound out of line.
posted by zippy at 4:00 PM on December 2, 2008

Your heater core has probably sprung a leak. If it keeps leaking, your car won't have any coolant, and it will ruin things. The $700 may be justified; replacing the heater core may involve tearing apart the entire dashboard. It should be pretty straightforward to call around and get estimates for replacing a heater core from various mechanics. If you don't want to spend the money for replacement, you could have the core bypassed completely, but that means you wouldn't have any heat.
posted by zsazsa at 4:04 PM on December 2, 2008

What will ruin your car is driving it without antifreeze. The heater core is used to heat the air that blows into the cabin when you turn the heat on. That heat comes from the engine, via antifreeze. Basically, a heater core is a little radiator with antifreeze constantly running through it. If it leaks, all your antifreeze can go bye-bye. If that happens, and you keep driving, your engine is done for. When the mechanic told you it would be okay to drive it for a day or so, he meant that the leak is probably slow enough that you'll still have enough antifreeze to cool the engine after a day or so of driving.

It sounds as if your mechanic thinks that you lost your antifreeze through a leak in the heater core. Heater cores are typically difficult and time-consuming to get to (buried, for example, way inside the dash board), and this is why replacement is expensive. You need to focus on asking why the mechanic concluded that the leak is in the heater core. Is he certain, or just guessing? If he's right, then you're stuck because it needs to be fixed and it will be expensive.
posted by jon1270 at 4:06 PM on December 2, 2008

I know nothing about cars, but anecdotally, my grandma has a 98 Camry and a few weeks ago she had to have the heater core replaced and it was $700. So if that is indeed the problem in your car that's probably not an unreasonable price. (The problem manifested for her in the car running sluggishly - my dad drove it and said it was only running on three cylinders. There were a couple of other problems though, so I'm not sure if that had anything to do with the heater core.)
posted by catatethebird at 4:08 PM on December 2, 2008

This is a heater core. The coolant from your engine runs through it so it can radiate heat into the cabin of the car.

Replacement cost on these things varies wildly. On some cars the mechanic needs to take apart the AC during the process. Its a tough part to replace and involves a lot of time.

Get a second opinion and ask them how many hours of labor its going to take. I wouldnt be surprised if the second mechanic quotes you a cheaper price, but be expected to pay around $500+
posted by damn dirty ape at 4:10 PM on December 2, 2008

Thanks for the answers! Here's a follow-up question: if it's so hard to get to the heater core, then how was Mechanic B so easily able to clean it out?
posted by lunasol at 4:20 PM on December 2, 2008

I think they just flush it with water. They dont need to remove it. Just disconnect two hoses from under the hood and run a garden hose through it.
posted by damn dirty ape at 4:38 PM on December 2, 2008

@damn dirty ape: yeah that makes sense. Oy.
posted by lunasol at 4:41 PM on December 2, 2008

It's possible that Mechanic B broke something when flushing the core, or maybe just didn't do a good job of reconnecting the hoses. You probably should go back to him and see if he guarantees his work.
posted by zsazsa at 4:42 PM on December 2, 2008

It's possible that Mechanic B broke something when flushing the core, or maybe just didn't do a good job of reconnecting the hoses. You probably should go back to him and see if he guarantees his work.

I was going to say the same thing. See if you can remember, or look on the receipt, what he actually did to clean it out. Did he just flush it? Then it's not his fault, the thing just gave out. But if he used some kind of drain cleaner kind of stuff, or was physically rodding it out with a coathanger, it could be his fault.

The reason it can be cleaned more easily than replaced is that the connectors where the water goes in and out are fairly easy to access. It's a lot harder to actually remove it. It's sort of under everything in the whole dashboard of the car.
posted by gjc at 5:20 PM on December 2, 2008

$700 indeed seems like a lot for a heater core, but it's almost all labor, so it all depends on how hard it is to change. (I thought my Grand Am had a hard to reach heater core, but it was only $250.)

Just to add to the info, it's not uncommon for a heater core or radiator to develop a leak, but debris in the system keeps it from actually losing any coolant. A pressurized flush can indeed clean out the system, and at the same time dislodge the debris that was holding back a full-blown leak.

Even if you keep the coolant topped off, the leak will get worse, and meanwhile your interior windshield and windows may well get coated with a filmy residue that will impede your vision.
posted by Fuzzy Skinner at 5:36 PM on December 2, 2008

You could probably get this part at an auto wrecker for a lot less than new.
posted by canoehead at 6:08 PM on December 2, 2008

Engine coolant is mostly water. A pump, usually driven by the fan belt, circulates it around the cooling system. It picks up heat as it runs through cooling channels in the engine block, then cools down again as it goes through the radiator.

The radiator is a heat exchanger. It has narrow passageways for the coolant to run through, and fins for air to blow through. Hot water goes in and cools down before circulating back to the engine block; cool air blows through and gets hot. The net effect is to remove heat from the coolant water and dump it into the air.

The heater core is just like a small radiator. Turning on your cabin heat control opens a tap that diverts some of the coolant water away from the main radiator loop and sends it through the heater core instead. A fan blows cool air through the heater core and into the cabin.

The thermostat acts as a temperature-sensitive blockage in the coolant circulation loop. The hotter the coolant, the more it opens up, and the more heat can get removed by the radiator (and the heater core, if that's switched in). The effect is to keep the engine working close to its intended operating temperature.

Thermostats are designed to fail fully open, allowing unrestricted coolant flow. This makes the engine run too cool, which will do far less damage than running too hot. It also means that the circulating coolant will be cooler than normal, which will warm the heater core less, which will make your cabin heating less effective. So if you notice that your heater is delivering lukewarm air instead of its usual toe-blistering goodness, and your engine temperature gauge is reading low, it's a fair bet that your thermostat has failed.

The water channels inside the radiator and the heater core are fairly small, to allow for enough contact between the coolant water and the metal walls to let the radiator do its job. The rest of the cooling system has much larger tubing or channels. If any part of your cooling system is going to get blocked, it will be the small channels in your radiator or heater core. Most such blockages are caused by corrosion and/or mud and/or assorted gunk.

Most of that, in turn, is caused by prolonged use of plain water to top up the cooling system in response to the usual gradual loss of coolant expected in older cars, and failing to flush the cooling system periodically and replace the coolant additives. These additives include anti-freeze, anti-boil and anti-corrosion chemicals. Your cooling system will still cool the engine just fine without these additives for as long as there is still proper circulation through all its parts - the point of the additives is to make sure that there will be proper circulation through all parts for as long as possible.

If your radiator has blocked water channels, it won't cool the circulating coolant properly, your engine will tend to overheat, and the coolant may boil. That will cause clouds of steam to escape from the pressure relief valve built into the radiator cap. If that valve fails, one of your coolant hoses will probably blow out, causing catastrophic coolant loss. That will make your engine really hot very quickly, and probably kill it if you keep driving.

If your heater core has blocked water channels, that won't affect the main cooling system, because the heater core is fed from a side loop off the main circulation path. But it will make the heater work less effectively. Depending how clogged it is, you might get anything from lukewarm to cold air coming out of the heater. The engine temperature gauge will still read normal, though, because the coolant in the main loop is still getting properly hot.

Apart from blockages, heater cores and radiators can leak. They corrode (possibly due to less-than-zealous attention paid to the chemical makeup of the engine coolant by previous owners). Bulk corrosion will do them in, but spot corrosion or cracked welds can cause small leaks that can get temporarily "repaired" by incidental gunk deposits or by deliberate application of specially engineered gunk specifically designed to fix small leaks in radiators. Finally, if your engine coolant is just plain water, and doesn't have the proper anti-freeze additives, and the water freezes inside the heater core on a cold night, then the pressure of expanding ice inside the small tubes will stretch and crack them, often to the point of gross failure.

With all that background in mind:

Mechanic A found no major problems, because everything worked. In fact the heater core may have been partially blocked by that stage, and may not have been delivering quite as much cabin heat as it did when new. That's a pretty subtle thing to spot in a mechanical checkover, and I wouldn't mark Mechanic A down for failing to notice it.

Mechanic B fixed your no-heat problem by changing the thermostat (which may or may not have been necessary, depending on whether the engine temperature was also lower than it should have been, but is cheap and easy and may well have headed off a subsequent thermostat failure) and flushing out the heater core to unclog it. This is done by disconnecting the rubber hoses that connect the heater core to the main circulation loop, which is usually easy because access to those is usually OK, then flushing with water in the opposite direction to normal circulation.

Mechanic C says your heater core is ruined, and has quoted you for replacing it. Replacing a heater core is, as others have said, hard.

But I'm a bit suspicious about that claim.

When a heat exchanger leaks - especially if the leak is gross enough to cause a cloud of steam - the liquid coolant will mix with the air that's blowing through that heat exchanger.

If the radiator fails, all that air is outside the cabin, and you will see that steam coming from under the hood.

But if a heater core fails, you will get hot engine coolant leaking into the air that's delivered to the cabin - and you will smell it, and notice it fogging your windows, well before you see steam coming from anywhere outside the cabin.

What I think is likely to have happened is that Mechanic B has been a little slack with the hose clamps, or the hoses connecting to the heater core have hardened over time, taken unkindly to being disturbed, and sprung leaks. This could cause coolant to escape under the hood without turning up inside the cabin.

How much additional damage has been done depends on why the steam stopped. If it stopped because you turned the heater control off, you're probably OK. If it stopped because you let all the coolant escape, you may be looking at a bunch of engine-overheated problems (such as a warped cylinder head) sooner or later. If it stopped because new gunk has re-blocked a recently de-gunked pinhole or a leak around a hose fitting - no immediate action is required, but you should be flushing the whole cooling system and replacing all the hoses fairly soon, and you should be keeping a close eye on your engine temperature gauge, and checking the coolant level at every fuel stop.

Something else to consider is what Mechanic C meant when he said there was no antifreeze. If he meant that your engine coolant was essentially plain water with no additives, then he is probably telling you that he thinks your heater core has been cracked by freezing. If, on the other hand, he meant that there was no coolant at all (as jon1270 seems to be assuming), then that is a consequence of a cooling system leak rather than a cause.

If that were my car, I would be doing the following:

1. Keep the heater tap turned off, and drive rugged up with the windows open until this issue is fixed.

2. Keep several big bottles of water in the car, and check the coolant level frequently while

3. taking it back to Mechanic B.

4. Checking the coolant afterwards to make sure it looks more like luminous green alien blood than plain water.
posted by flabdablet at 7:46 PM on December 2, 2008

WOW, flabdablet, thank you so much for that very detailed explanation.

So if you notice that your heater is delivering lukewarm air instead of its usual toe-blistering goodness, and your engine temperature gauge is reading low, it's a fair bet that your thermostat has failed.

This is exactly what was happening before I took it to get fixed, though the air was more cold than lukewarm. Also, should the temp gauge be right at the middle? It's always a bit below middle.

And:

Keep the heater tap turned off, and drive rugged up with the windows open until this issue is fixed.

What do you mean by "rugged up?"

Thanks again. This is why I love AskMe.
posted by lunasol at 8:40 PM on December 2, 2008

What do you mean by "rugged up?"

Oh, never mind, got it. :)
posted by lunasol at 9:09 PM on December 2, 2008

You should be watching your temp gauge while you're driving it before you get it fixed. If it starts to climb, stop and turn off the engine!

The temp gauge shouldn't necessarily be right at the middle. This is actually determined by your thermostat, and they have differing ranges. It's fine below. Just watch it when it starts to climb.
posted by luckypozzo at 9:59 PM on December 2, 2008

The design operating temperature for most engines is around 80°C (180°F) and that's what you should be getting with a new thermostat. Unfortunately, most dashboard temperature gauges are not calibrated, and any markings they do have are fairly meaningless. However, you can check whether your new thermostat is working by seeing whether the temperature gauge settles to pretty much the same spot on a warm day as it does on a cold one. If it's doing that, then you should regard the spot where it settles as meaning "normal temperature". That has in fact turned out to be a bit below the middle in every car I've driven.

Don't sweat it if the gauge rises a little bit when the engine's working hard on a very hot day, or falls a little bit when it's coasting on a very cold day; temperature regulation isn't perfect. If it persistently sits right down at the C end, go back to mechanic B for a new thermostat. But if you see it getting up near the H end or if you see steam coming out from under the hood: pull over, wait ten minutes for the engine to cool some, then carefully crack open the radiator cap and put more water in before you do anything else.

To avoid burns, use a huge wad of rag between your hand and the cap, and use the same slow cap-removal technique as you would for a bottle of Coke that's been dropped and shaken. Bear in mind that your cooling system is designed to work at higher than atmospheric pressure, and if the coolant is close to boiling point while under pressure with the cap on, it may be well and truly above boiling point when the cap comes all the way off and cause a steam explosion. You don't want to be standing near a steam explosion. Be patient and let the thing cool down for ten minutes before cracking the cap.

After the cap is removed, start the engine again before slowly pouring in the top-up water. This will help the new, cold water mix gradually with the existing hot water instead of all arriving at the engine block in one great cold slug. You don't want a cracked engine block either. Topping up with the engine running also lets you see and hear whether the water is actually circulating. If it isn't, and you can't see a broken or missing belt, your water pump is probably stuffed.

You will generally still get some coolant circulation even with a stuffed water pump due to thermosyphon action, but it won't be enough to let the engine do much real work. Keep an eye on the gauge while you limp home, and keep topping up the water as required.

You can safely limp home with the radiator cap off, and doing so will mean you can pull over and do top-ups every few minutes if necessary without risking steam explosions. It also means that the coolant inside your engine block will boil at 100°C instead of the higher temperature it would reach under pressure, which lessens the chance of bad engine damage even if no thermosyphon circulation is in fact happening.

Boiling, though it's a clear sign of cooling system failure, is actually not such a bad thing for the motor. It's when the boiling stops that the real damage occurs. Consider a pot of water boiling on the stove. It doesn't matter how high you turn up the burner - the pot won't get any hotter than boiling point until all the water is all gone, at which point you will burn the arse out of the pot. Keep the water topped up, and the pot will survive indefinitely. If you suddenly dump all the boiling water down the sink and run cold water into the pot, the bottom will warp. Engines, to a good first approximation, react the same way.
posted by flabdablet at 1:52 AM on December 3, 2008

Update:

I took the car back to Mechanic B. He was quite certain the problem was a loose clamp, so he put some new clamps on for $50. It's been 24 hours and so far, so good. Flabdablet, I looked at the coolant tank afterwards and it did indeed have green alien blood in it. I'm going on a road trip next week and will make sure to check the coolant at every fuel stop.


Thanks again for the advice! You all just helped me save $650.
posted by lunasol at 1:33 PM on December 4, 2008