Ford Ka '98 coolant boiling

Question

Vehicle: Ford Ka 1998 1.3L - Endura Engine

What's happens:

• start engine
• wait a few minutes (10-ish)
• coolant starts pouring out from where two hoses like this one interconnect (I'm assuming it's a coolant hose)

After I stop the engine:

• in a few minutes the leak stops
• you can hear some faint hissing under the bonnet
• you can also hear pops (like a hot exhaust cooling)

This does not seem to happen when the vehicle is moving, only when stationary for a while with the engine running.

Things I've tried:

• burping the car
• removing thermostat
• since it doesn't have a temp gauge, I attached an OBD adapter -- coolant started leaking at 81°C -- kind of early to be an engine overheating issue?

Other (maybe relevant notes):

• cabin fans give warm air on both hot/cold setting

• the hose that goes to the overflow tank is really hot

• the hose from the thermostat is also very hot, and I think it's bulging

I've been to a shop and they said it's probably the head gasket, but they can't say for sure.

Are there any other (cheaper) things I can check before committing?

The leak started at about 81°C:

Bulging? Thermostat hose:

Wider view of bulging? Thermostat hose:

The hoses that go into the coolant overflow tank are very hot

Thermal camera view of the hoses that go into the coolant overflow tank:

https://i.sstatic.net/n2mfu.jpg

Answer 1

Before you commit to getting a new head gasket, there are two things you can do:

First, replace the expansion tank cap. The plastic container with the two hoses on it has the yellow cap. This provides the pressure for your system, which is required in order to properly run. If this is not keeping enough pressure in your system, it will allow the coolant to overflow and boil. Most vehicles have their thermostat at around 85-90°C (185-195°F). If yours is boiling at 81°C, this could be a likely cause.

Also, looking at the pictures, the expansion take has a small amount of fluid dribble next to the cap. I don't know if this is your doings, or if it's that way for some other reason, but if you haven't messed with it, this could be showing you the cap is not air tight and is leaking.

One other thing is, since coolant is flowing in and out of this expansion tank, it will be hot. That's regular engine heated coolant flowing in and out of there ... it will be near engine temp, so expect it to be hot. The reason for this tank is actually to allow the cooling system to burp itself and to provide you a visual means to tell if your system needs more coolant.

Secondly, if a new cap doesn't do the trick, you can also check to see if there are hydrocarbons in the coolant system. There are devices which you can buy which will tell you right off if there are. If there are, you will need to have engine work done, because normally there should be no hydrocarbons in the coolant system. This Mech.SE answer can help you with that.

One other thing ... you need to consider changing out the hoses which are bulging. This is showing you these are getting to end of life. Just like a chain, the cooling system is only as strong as it's weakest link ... those are looking like mighty weak links.