Overflow Coolant Boiling

I had an issue where the coolant in my radiator overflow tank would boil after about 5 - 10 KM drive. I would loose about 1 - 2 l of coolant every time. This boiling would happen even after the engine is switched off.

While I am a computer engineer, I know a few things about cars too as I was curious to be a mechanic when I was a child.

Head Gasket?

From my understanding this could have been a radiator issue or a blown head gasket. If it is the latter the repair could be very costly about US$ 1000 or Rs. 150,000 depending on the vehicle.

If it is a head gasket issue, unburnt hydrocarbons could enter the cooling system and get dispersed through it. If this is the case the engine will not run smooth and if you keep the radiator cap open you will notice bubbles coming out from within. There are various tests to confirm this, but it was unlikely that I had the issue as I didn’t see any bubbles coming out or the engine misfiring.


This left the radiator the culprit. A radiator blockage could result the engine to overheat and in return make the coolant boil. The temperature gauge reads that the engine is in ideal operating temperature. Also looking in to the condition of the radiator, I doubted it would be in a bad shape.

I checked the Radiator cap and it looked fine. It was replaced in a recent service at Toyota Lanka and on inspection it looked fine. So I feared the worst. When I contacted Toyota I had scary news with the possibility of needing to replace the whole radiator.

So I took the chance and bought a $5.00 (Rs. 800) radiator cap. For my surprise it solved my problem and saved me a ride to Toyota, for now.


If you are having coolant loss, change the Radiator cap. Its cheap, cheaper than the petrol it takes to go to a dealership. Start there.

How ever I will be importing a new Radiator and replacing mine. That is because of a different issue I have. But now there is no rush.

TLDR; My Backstory

I own a Toyota Camry 2008 which suffered a failed radiator fan motor which resulted the plastic (actually Nylon) cover of the radiator to crack. This happened in middle of nowhere just before midnight. I had to walk a little to go for a “night shop” to fetch water. I had to top up water 2 more times in the remaining 100 KM of my journey.

The fix according to Toyota is the full replacement of the radiator which it self costs Rs. 120,000 (about US$ 800). That is not an issue for me. The problem is that it will take just short of 2 months come from Japan.

I am a professional and I need a car. Waiting 2 months without a car is a huge inconvenience. Hiring another car for 2 months is an unnecessary cost.

Thus, I went to an independent radiator shop. The guy replaced the Nylon top with a Chinese after market product. This cost me about $50 (SL Rs. 7500).

This is when I started loosing coolant. I feared a leak. On further inspection I noticed that the overflow tank (as some of you call - the reserve) was bubbling / boiling. For a moment I thought it was a blown head gasket. You can blow your head gasket if you fill cool water while the engine is hot. In this case the engine has to be running. But then I noticed it couldn’t be. That is when I looked in to the radiator cap and replaced it fixing my issue.

Now there is no urgency to replace the Radiator. I will drive to Toyota Maharagama and place an order for a new Radiator and Radiator fan after the Sinhala Tamil New YEar which they will open on 18th. That is because, while the radiator system may hold up fine, I really really hate to get stranded because I wanted to save $800.00. Fro me, its not worth it.