Technical Engine overheating

[seba]

Car: Fiat Punto 1.2 16V petrol

So, I had no problems with the driving of the car (no strange noises, no overheating), then the car was parked for ~6 h (so totally cool engine).

Then I've started it (also no weird sounds) went on the motorway, went from it (this took ~5-10 min in total) and then the engine temperature was starting to go up really fast until the red light went on, so I've stopped the car. Opened the bonnet (temperature went quickly to normal), shook a bit the temperature sensor to see if it's maybe malfunctioning (jittery reading or something), but it was all ok. The area near the sensor was indeed warm. Then I've checked the coolant, the coolant was cold so I've opened it slowly, but it sprayed all around (so it was under pressure). The coolant was all there, so no missing coolant. Electric fan is working. I've proceeded to drive further as the temperature seemed ok, after ~500 m same happened. I've put cabin heating at full + heater fan, but the air wasn't hot.

What do you think it could be?
I was thinking clogged hoses, water pump failure or thermostat failure (albeit not a normal failure mode of it).

Any tips on how to differentiate? I was thinking of using a thermal camera to see maybe something and then try to change the thermostat with a new one and test the old one if it works.

 

[joncoxon]

If coolant was cold yet under pressure perhaps it could be head gasket? exhaust gasses leaking into cooling system, any white smoke from the exhaust? or mayonnaise looking deposit on oil filler cap? you could start from cold with coolant res cap of and see if you get bubbles of exhaust gas come through it. A compression test will tell you more. that's what I'd do first


Jon

 

[oldhammer]

Hi seba.


Is the Radiator fan cutting in? (working)


Also are you getting Heat from the Heater?




Never open the Expansion cap until the car as cooled down good and properly
You are lucky not to have been scalded,

 

[Neilycus]

Head gasket sounds like its gone badly.

 

[varesecrazy]

agreed - but said water was COLD - but obviously pressurised

said heater was COLD - so obviously a non-flow situation,

need more background really for better diagnosis..,

Charlie

 

[Ziggy122]

If the car is getting too hot

You have no heaters
No coolant loss

And there is pressure
It sounds very odd as it sounds like water pump and thermostat issues have failed together?
Or a massive air lock

Sounds like you should get a coolant pressure test to ensure there are no leaks
And check for trapped air

Ziggy

 

[FRS1810]

Or sounds like your thermostat has failed and is stuck in the closed position, this would cause overheating an virtually no coolant will get to the rad, another possibility is the water pump has failed mechanically and isn't circulating coolant,

To test thermostat when the engine has been run is the top rad hose hot?

Water pump when the engine is running you should have coolant coming from the small return hose to the coolant/header tank

 

[seba]

Head gasket: I doubt that. If it would be that, it would deplete the cooling liquid. Haven't checked the oil yet. I don't remember any white fumes. I've had a head gasket failure on an another car, this doesn't look like it.

As I've said, both fans work. It could be that heater produces slightly warm air or it could be that it's totally cold. Couldn't really tell as I had really cold hands, but definitely it wasn't hot. Removing the expansion cap wasn't really a scalding danger as I've described at start, the cooling liquid was cool.

Yes I thought of air locks, any clue on how to check for that? That's why I also was thinking about thermal camera. I hope I could see with it for air locks, clogging, etc.

Why would the top rad hose be hot? Isn't the thermostat on the engine block, therefore hot liquid wouldn't come to the top rad hose?

I suspect that the return liquid wouldn't work with a thermostat being stuck closed?

 

[joncoxon]

Head gasket: I doubt that. If it would be that, it would deplete the cooling liquid. Haven't checked the oil yet. I don't remember any white fumes. I've had a head gasket failure on an another car, this doesn't look like it.

As I've said, both fans work. It could be that heater produces slightly warm air or it could be that it's totally cold. Couldn't really tell as I had really cold hands, but definitely it wasn't hot. Removing the expansion cap wasn't really a scalding danger as I've described at start, the cooling liquid was cool.

Yes I thought of air locks, any clue on how to check for that? That's why I also was thinking about thermal camera. I hope I could see with it for air locks, clogging, etc.

Why would the top rad hose be hot? Isn't the thermostat on the engine block, therefore hot liquid wouldn't come to the top rad hose?

I suspect that the return liquid wouldn't work with a thermostat being stuck closed?

The thermostat is at the top of engine and opens letting water into the top hose then to the radiator, this drains down through the radiator and out through bottom hose and back to the engine at the bottom. You have a pressure build up somewhere. if the water cant circulate it the heat from the engine will boil the water inside the engine and raise the pressure in the system. Likewise if the head gasket is blown then gasses on the compression/power stroke can be forced into the cooling system and raise pressure.


if you start engine, Ideally with 2 people, one holds top hose while engine gets warm see if it gets hot. the other keeps an eye on the gauge to make sure it doesn't over heat.


Is the thermostat removable? and just replace the housing, would rule out that part. as water could flow freely. Just replaced my mercs for jamming open

 

[Ziggy122]

The thermostat isnt removable
They come as one with the housing

Ziggy

 

[joncoxon]

Oh right like the Mercedes then. Which I'd like to add is constantly going wrong at the moment. Awaiting many tools to fix it, yet again.

 

[seba]

I have replaced the thermostat (16 eur at the local shop). The old thermostat was closed. I've then put the old thermostat in boiling water and it opens just 1 mm.

Now it's much better, I could get home (~50 km driving), but if I'm standing for a longer time (10+ min) it overheats. Also there is air coming in the cooling system. Probably a head gasket failure due to thermostat failure.

I've checked the oil and it's still nice, same holds for cooling liquid.

 

[fingers99]

Compression test5 (or coolant pressurisation test done by someone competent). Rule HG failure in or out.

 

[Ziggy122]

is the temperature sensor lying i wonder?

Ziggy

 

[seba]

Ok. Head gasket failure confirmed. Opened today.

Normal spark plug and spark plug from the 4th cylinder (black).

Right is the 4th cylinder, nicely half-washed from the gasket leak.

Bad combustion (left) due to this defect.

The gasket failure:

Pump is in perfect shape:

Old thermostat which has been replaced:

Thermostat while boiling.

It seems that the thermostat works now. The first day (when I've removed it) apparently it didn't open, although I wasn't the witness to the test.

 

[Ziggy122]

the compressable ring detached from the gasket allowing the coolant to flow in from the water channel

I'd decoke all the cylinders and heads while your there my friend

Ziggy