5

After driving some time, is it normal that the plastic spillover coolant tank, usually attached to the fan housing, that takes boiling overflow, get so hot that you get bubbles boiling out of it even though the engine itself, according to the temperature gauge on the dashboard, does not get overheated? Is it an indicator that the engine borderlines overheating? Or is it a normal occurrence to have it boil?

I just recently had some overheating issues on my 4wd Tacoma and, after replacing the thermostat, water pump and radiator cap, the truck drives fine WITH JUST TAP WATER IN THE COOLANT SYSTEM (which I will replace with real coolant after I'm done testing) but, when I check the coolant spillover tank right after driving, I see it mildly boiling and I'm curious if that's a sign of potentially more overheating or is normal. So maybe I thought it was getting to a simmering point because it's just water and not 50/50 mix.

coolant spillover tank

amphibient
  • 6,653
  • 40
  • 92
  • 129

2 Answers2

5

What you are describing is usually caused by a weak radiator cap. Weak meaning it is no longer holding the pressure which is needed inside the system. Since you said you just replaced the cap, having just water in the system will lower the boiling point and may cause over pressure in the system. You'll also want to ensure you have the entire system burped of all air, which also causes hot spots inside the engine. Easiest way to do this is to fill it from the radiator with the front of the truck pointing uphill.

When you do get this fixed, you'll need to ensure you drain the entire system to get the tap water out. Then you'll want to refill with 50/50 mix which utilizes distilled water instead of tap water, which will introduce minerals and contaminants into the system which degrades it over time.

Pᴀᴜʟsᴛᴇʀ2
  • 156,290
  • 29
  • 252
  • 491
  • It could also mean there is air in the coolant circuit and it's being purged into the tank. Especially since they did work on the circuit. – Captain Kenpachi Jun 01 '15 at 11:33
  • @JuannStrauss - I would expect a small amount of air to purge this way, not for it to be boiling over, though. – Pᴀᴜʟsᴛᴇʀ2 Jun 01 '15 at 11:35
  • Which is why I put this as a comment to an existing answer for the sake of completeness. You would be surprised how violent the purging can be. – Captain Kenpachi Jun 01 '15 at 11:37
  • @JuannStrauss - Fair enough. Thanks for the addition! :-) – Pᴀᴜʟsᴛᴇʀ2 Jun 01 '15 at 11:41
  • i found these instructions for burping the cooling system: http://www.instructables.com/id/How-to-Burp-your-cars-cooling-system/. What struck me as odd is that it calls to run the engine with the funnel in the radiator intake and not the rad cap. isn't that gonna cause a sh*tstorm of fluid blowing out of the rad as soon as the thermostat opens up ? – amphibient Jun 01 '15 at 16:39
  • yet the freakiest prospect of all is that it is boiling because head gaskets are blown... – amphibient Jun 01 '15 at 23:24
  • 1
    @amphibient - Since the vehicle is not overheating, I don't think this is a concern. – Pᴀᴜʟsᴛᴇʀ2 Jun 02 '15 at 01:42
  • Unless your tap water is extremely bad and you're not using antifreeze, there's no real benefit to using distilled water. The antifreeze contains far more minerals and chemicals than any tap water, including corrosion inhibitors. No drinkable tap water contains sufficient corrosive chemicals to affect your cooling system. – barbecue Sep 26 '15 at 15:40
  • 1
    @barbecue - and I would highly disagree with you. While antifreeze contains corrosion inhibitors, the minerals in tap water will fall out of suspension and create sediment. These sediments builds up over time and lowers the ability of the cooling system to do its job. There's no reason to be adding sediment when you don't have to. You don't know what exactly is in your tap water. Distilled water is just that: water. Pure and simple. – Pᴀᴜʟsᴛᴇʀ2 Sep 26 '15 at 15:50
  • @Paulster2, my point is not that there are no minerals, it's that the amount is trivial compared to the minerals found in the antifreeze itself. The amount of sediment in a gallon of water is far too small to have a serious impact on any cooling system. I'm not saying there's no deposits, I'm saying they are unimportant. – barbecue Sep 26 '15 at 16:07
  • @barbecue - Show me a credible reference which says not to worry about using distilled water and I will agree with you. Sediment is a real worry inside a cooling system. Adding more is not going to make things better, that's for sure. – Pᴀᴜʟsᴛᴇʀ2 Sep 26 '15 at 16:18
  • @Paulster2, I'm not sure what you would consider a credible reference. I find many references to people recommending distilled water, but very little actual evidence that this provides any real benefit. Obviously if you have extremely bad water it might have some impact, and I did mention that in my original comment. You're asking me to provide evidence that something is not true. That's pretty difficult. – barbecue Sep 26 '15 at 16:36
  • @barbecue - No, I'm not asking you to provide evidence something is not true. I'm asking you to provide evidence something is true. I'm not asking you to prove a negative. I'm saying there aren't any credible sources out there which say what you are saying. Until you can show me that, what you are suggesting is only your opinion. We try not to deal with opinions on this SE site, but rather fact. I agree with you that tap water isn't going to have a huge amount of these things in them, but that doesn't mean we shouldn't worry about it. – Pᴀᴜʟsᴛᴇʀ2 Sep 26 '15 at 16:41
  • I'd also point out that you're unlikely to find true distilled water in shops, you're probably getting deionized water instead. In fact, conventional wisdom in manufacturing is that deionized water actually corrodes metals faster. I haven't seen any real evidence either way. – barbecue Sep 26 '15 at 16:42
  • Let us continue this discussion in chat. – barbecue Sep 26 '15 at 16:43
1

I had the same problem with my car and finally it was the Thermostat who was the culprit, it was not working properly and due to that even when the engine was heating up it did't start the Cooling fan and then ended up with the lots of heat and pressure and due to that coolalnt fluid overflows. Now I got the Thermostat replaced and its first day and i did't experience the same problem again and hoping it should run successfully now. ~Sanjiv

Sanjiv Lalit
  • 21
  • 1