# Why is my car overheating? **URL:** \ **Category:** Factual Questions\ **Created:** [January 9, 2003, 12:20am UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399 "2003-01-09T00:20:33Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![Fiver](https://avatars.discourse-cdn.com/v4/letter/f/e274bd/32.png) [@Fiver](https://boards.straightdope.com/u/Fiver)\ **Post date:** [January 22, 2003, 5:49pm UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/41 "2003-01-22T17:49:42Z")
Yesterday before leaving the house I lifted the hood and opened the radiator. Its level was very low; I couldn’t even see any coolant and the uppermost finwork was bone-dry. Also, the auxiliary coolant tank was empty. It took over half a gallon to top off the radiator, then I refilled the auxiliary tank. Once I’d done this, the weird idling problem ceased. So, there’s definitely a leak somewhere, but there’s no puddle on the pavement under the car. The fan, fan belt and water pump are all (seemingly) fine. I haven’t been able to determine if there’s white smoke coming out of the exhaust. Isn’t the exhaust white-ish anyway? What’s wrong with my car? ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [January 22, 2003, 6:08pm UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/42 "2003-01-22T18:08:25Z")
_What’s wrong with my car?_ It has a coolant leak. 😃 It may be leaking in a place where it evaporates before enough builds up to drip. A cooling system pressure test would almost certainly find it. If you’re lucky, tightening **ALL** the coolant hose clamps might fix it. By all, I mean radiator, heater, bypass, throttle body, whatever-it-has hoses. A blown head gasket is not out of the question, but if that is the case, it doesn’t sound serious **yet** (it will get serious). If the pressure test doesn’t help, a combustion leak test would be in order. In cold weather, it’s not unusual to see some water vapor coming from tailpipes. Some cars put out more than others. It’s when there are great billowing clouds of white “smoke” that a head gasket leak is indicated. ---
**Author:** ![Fiver](https://avatars.discourse-cdn.com/v4/letter/f/e274bd/32.png) [@Fiver](https://boards.straightdope.com/u/Fiver)\ **Post date:** [January 22, 2003, 6:33pm UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/43 "2003-01-22T18:33:15Z")
Thanks, **Gary T**! Given that this problem began right after the oil-change place did the diagnostic on my emissions-system problem, is it conceivable that they did something to cause this problem? And, will my car pass emissions inspection as is, or will I have to fix the leak first? ---
**Author:** ![NurseCarmen](https://avatars.discourse-cdn.com/v4/letter/n/5daacb/32.png) [@NurseCarmen](https://boards.straightdope.com/u/NurseCarmen)\ **Post date:** [January 22, 2003, 6:35pm UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/44 "2003-01-22T18:35:42Z")
> [@](#): > > \*Originally posted by Fiver \* > **So, there’s definitely a leak somewhere, but there’s no puddle on the pavement under the car…Isn’t the exhaust white-ish anyway?** You very well could be seeing no puddle due to the fact that is being superheated and escaping your engine as a gas. Sadly, the way it does this is via a head problem. An auto at normal operating temp at idle will appear to be producing no exhaust (unless it is cold out, then some steam will be seen, but will dissapate quickly) Bummer. Looks like a slow leak. ---
**Author:** ![NurseCarmen](https://avatars.discourse-cdn.com/v4/letter/n/5daacb/32.png) [@NurseCarmen](https://boards.straightdope.com/u/NurseCarmen)\ **Post date:** [January 22, 2003, 6:44pm UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/45 "2003-01-22T18:44:41Z")
> [@](#): > > \*Originally posted by Fiver \* > \*\*Given that this problem began right after the oil-change place did the diagnostic on my emissions-system problem, \*\* :smack: D’oh! More info to add to the puzzle. I don’t see why they would have come even close to cooling system hoses while tracking an emissions issue. Sadly, I’ve seen some clueless folks standing under cars at some of those chain shops (Note: This is usually the exception, not the rule) ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [January 22, 2003, 8:41pm UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/46 "2003-01-22T20:41:05Z")
_Given that this problem began right after the oil-change place did the diagnostic on my emissions-system problem, is it conceivable that they did something to cause this problem?_ Anything’s possible. However, if understand correctly, your first overheating incident was the same day they did their inspection. Then later, after you did your repairs and got the cooling system full (or close to it), the car did OK for over a week before running hot again. So far, the evidence given indicates it overheats because it gets low on coolant, and it gets low because there’s a leak. If it takes 8 or 10 days to leak enough to overheat, I don’t see how something they did made it overheat the same day. _And, will my car pass emissions inspection as is, or will I have to fix the leak first?_ I don’t know why a coolant leak would have any bearing on an emissions inspection, unless A) the car is showing symptoms at the time of the inspection (we’ve already seen that this affects idle control, it probably affects fuel mixture as well) or B) there is a blown head gasket, with antifreeze going through the exhaust. ---
**Author:** ![Rushgeekgirl](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rushgeekgirl/32/3715_2.png) [@Rushgeekgirl](https://boards.straightdope.com/u/Rushgeekgirl)\ **Post date:** [January 22, 2003, 9:24pm UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/47 "2003-01-22T21:24:53Z")
When you say you don’t see indication of leaking, are you checking the back of your car? Because this morning as my friend was examining my problem, he noticed antifreeze spray out the tailpipe. He added some sort of sealant to my radiator this morning hoping the smoke would settle enough for me to drive across town to the repair shop. No help at all. ---
**Author:** ![Fiver](https://avatars.discourse-cdn.com/v4/letter/f/e274bd/32.png) [@Fiver](https://boards.straightdope.com/u/Fiver)\ **Post date:** [January 23, 2003, 12:26am UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/48 "2003-01-23T00:26:15Z")
I took it back to the oil-change place. I explained what was going on, and one of the guys there pulled out the dipstick. There was coolant on it. He said that since it’s taking so long to leak significant amounts of coolant, it’s possible I could fix it with a can of “K&W (something)”. It’s a fluid that runs through the cavity and seals any leaks it finds, and _sometimes_ saves the expense of removing the manifold, timing belt, etc. to get at and replace the head gasket. It requires draining the oil first, but the guy at the shop told me he’ll do that for me without charge, since I’ve just had the oil changed recently (last month). I sure hope this works, since I’m currently unemployed and the $4-600 it would cost to replace the gasket is pretty hard to part with right now. Good call, **Violet** , **Booker57** and (sort of) **SandyHook**. ---
**Author:** ![Violet](https://avatars.discourse-cdn.com/v4/letter/v/ebca7d/32.png) [@Violet](https://boards.straightdope.com/u/Violet)\ **Post date:** [January 23, 2003, 12:43am UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/49 "2003-01-23T00:43:56Z")
Thanks for reporting back, **Fiver**. Hope this isn’t a costly repair for you. Looks like you really tried to touble shoot the matter. ---
**Author:** ![Booker57](https://avatars.discourse-cdn.com/v4/letter/b/b9e5f3/32.png) [@Booker57](https://boards.straightdope.com/u/Booker57)\ **Post date:** [January 23, 2003, 1:36am UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/50 "2003-01-23T01:36:44Z")
K&W Block Seal. Goood stuff. Bit of a hassle to do. Many steps. 1. Drain cooling system. 2. Flush cooling system. 3. Fill cooling with water and block seal. 4. Run engine for 15-20 min. 5. Let engine cool, drain system. 6. Leave it alone for 12 hours. 7. Refill cooling system with correct amount of anti-freeze and water mix. There are probably more steps, it is complicated. But when it works it works. Warning: it does not always work. ---
**Author:** ![Fiver](https://avatars.discourse-cdn.com/v4/letter/f/e274bd/32.png) [@Fiver](https://boards.straightdope.com/u/Fiver)\ **Post date:** [January 23, 2003, 3:13am UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/51 "2003-01-23T03:13:18Z")
But does it _usually_, or even _often_, work? I’m on the horns of a prisoner’s dilemma here; I can go to the trouble and expense of the block seal and maybe save the cost of the gasket replacement. Or, go to the trouble and expense of the block seal and have it all be for nothing, and I’ll still have to pay for the gasket replacement. ---
**Author:** ![Violet](https://avatars.discourse-cdn.com/v4/letter/v/ebca7d/32.png) [@Violet](https://boards.straightdope.com/u/Violet)\ **Post date:** [January 23, 2003, 3:39am UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/52 "2003-01-23T03:39:14Z")
The K & W people have a web site, with toll free number and email address for questions: [http://www.kandw.com/faqs.html](http://www.kandw.com/faqs.html) ---
**Author:** ![Fiver](https://avatars.discourse-cdn.com/v4/letter/f/e274bd/32.png) [@Fiver](https://boards.straightdope.com/u/Fiver)\ **Post date:** [January 23, 2003, 3:52am UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/53 "2003-01-23T03:52:14Z")
Of course, **Violet** , but I can already guess what they’re going to tell me. ---
**Author:** ![Rushgeekgirl](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rushgeekgirl/32/3715_2.png) [@Rushgeekgirl](https://boards.straightdope.com/u/Rushgeekgirl)\ **Post date:** [January 23, 2003, 5:15am UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/54 "2003-01-23T05:15:20Z")
I just bought the K & W Block Seal at Autozone for 6.99. It’s worth a shot, I’d think, even if it’s a hassle. I think it’s probably too late for me, but I’ll try anything because I cannot pay the six hundred I was quoted tonight. ---
**Author:** ![Fiver](https://avatars.discourse-cdn.com/v4/letter/f/e274bd/32.png) [@Fiver](https://boards.straightdope.com/u/Fiver)\ **Post date:** [January 23, 2003, 7:06pm UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/55 "2003-01-23T19:06:02Z")
Good luck with that, **Rushgeekgirl**. ---
**Author:** ![Fiver](https://avatars.discourse-cdn.com/v4/letter/f/e274bd/32.png) [@Fiver](https://boards.straightdope.com/u/Fiver)\ **Post date:** [January 24, 2003, 4:13pm UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/56 "2003-01-24T16:13:58Z")
**Gary T**? Anything to say about Block Seal? ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [January 24, 2003, 6:37pm UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/57 "2003-01-24T18:37:52Z")
I’m not familiar with the K&W product. There are a number of different brands of similar stuff, and from what I gather the effective ingredient is sodium silicate. I did an archive search on an internet network of auto repair pros, and found 8 reports of these products (various brands) working and 5 reports of their not working. So from what I can find, you’ve got a better than 50% chance of it working. I wouldn’t count on it being a permanent fix, but if it works in your case it will likely last for many months (some reports indicated over a year). One potential problem is clogging of the radiator, heater core, or engine coolant passages. Whether it works on the intended problem or not, there is a risk of creating a different problem. The only brand of cooling system stop-leak I like to use is Bar’s Leaks. I don’t know if it has sodium silicate, though my feeling is it doesn’t. I trust it because although my whole career I’ve heard warnings about stop-leak products clogging radiators and heater cores, I’ve never seen that happen with Bar’s Leaks (not saying it can’t, however). Also, it is recommended by some auto manufacturers as a preventive. More often than not, it stops leakage for some time. I have never tried to use Bar’s Leaks for a head gasket problem, **however** …one of my customers had a car that suddenly started blowing huge clouds of white steam out the tailpipe, with a corresponding loss of coolant. In desperation, he put some Bar’s Leaks in it and it solved the problem! Turns out 2 of the 8 positive reports I mentioned above were with Bar’s Leaks. I guess if I were to try this method of addressing a head gasket leak, I’d try Bar’s Leaks first, though it seems other brands can work also. Some of what I read indicated that the sodium silicate does not work if there’s any antifreeze present. With that in mind, I’d be inclined to flush the cooling system twice with plain water to increase the chance of its working. ---
**Author:** ![Fiver](https://avatars.discourse-cdn.com/v4/letter/f/e274bd/32.png) [@Fiver](https://boards.straightdope.com/u/Fiver)\ **Post date:** [January 24, 2003, 10:27pm UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/58 "2003-01-24T22:27:30Z")
Yes, my mechanic said we should flush both the oil and the cooling system, because of the antifreeze concern. I’m not sure I understand how coolant is getting into my crankcase. Isn’t the cooling system supposed to be closed, just like the oil system? It seems like there should be a leak in the cooling system as well as the head gasket, for coolant to be mixing with my oil. Where does the cooling system meet the head gasket? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [January 24, 2003, 10:36pm UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/59 "2003-01-24T22:36:06Z")
Both coolant and oil flow through the head via holes which are normally kept separate by the head gasket. If a portion of the gasket is ruptured between these two pathways, then oil and coolant are free to mix, which they do. ---
**Author:** ![Fiver](https://avatars.discourse-cdn.com/v4/letter/f/e274bd/32.png) [@Fiver](https://boards.straightdope.com/u/Fiver)\ **Post date:** [January 31, 2003, 5:01am UTC](https://boards.straightdope.com/t/why-is-my-car-overheating/147399/60 "2003-01-31T05:01:52Z")
**Rushgeekgirl** , come back here and tell us if the block seal worked for you. I’m trying it in the morning. [Previous page](https://boards.straightdope.com/t/why-is-my-car-overheating/147399.md?page=2)