Fabia 1.2 HTP overheating troubleshooting.

[Gaborr]

Hello everyone.

 

I've got a mk1 with the 1.2 HTP 12V engine and I've been having some issues with overheating and I'd appreciate some help with diagnosing. 

 

I'll list the events that led to this point in chronological order and put some more points below. 

 

Car was initially just loosing coolant slowly but the temp gauge sat steadily in the middle - >Assumed the HG had failed ->  garage checked compression and checked for leaks and they found none and compression was ok- > replaced coolant cap - > lost some more coolant - > garage put some leak block in the coolant. 

 

Issue seems to be fixed.

 

Then the winter came and the car had not had heating for a while, I've checked the heater core pipes and one was cold the other was hot.

 

Ive asked the garage to flush the heater core, they said the thermostat was faulty and replaced it. 

 

The car had heating but then on the way home it overheated out of nowhere. Went back to be flushed and bled a few times, but the issue never went away. 

 

The car wouldn't overheat when idling in the garage but after about 30 minutes of driving the temp gauge would start creeping up. 

 

The current symptoms of the car: 

 

- temp gauge sits in the middle for about 30 mins then car heats up fairly quickly

- top radiator hose hot and hard 

- bottom hose and radiator are cold 

- fan doesn't kick in 

- no heat when the engine is idling, heater blows warm when the engine is revved up. 

- when the temp starts going up, stopping and revving the engine bring the temp down quickly. 

- The morning after there is no pressure in the expansion cap, however the coolant goes above the max level. 

- car doesn't smoked white and is not loosing coolant. 

 

I'm quite lost as to what could this be, airlock, failing water pump, blocked radiator, or the headgasket failing? 

 

Here is a video I took when I was checking if the water pump is circulating properly. I'm not sure if that bubbling is normal or not.

 

https://youtube.com/shorts/S3dUrjo3o8s?si=4qLkDUg6XXwZk_bI

 

If anyone has any input on this it would be greatly appreciated.

[Paws4Thot]

2 hours ago, Gaborr said:

garage put some leak block in the coolant. 

 

Issue seems to be fixed.

- top radiator hose hot and hard 

- bottom hose and radiator are cold 

I think these are the main relevant points; the garage has at least part blocked the radiator with its "Leak Bodge" gunk.

[Breezy_Pete]

That bubbling is definitely not normal. There should be a trickle of liquid coolant, which speeds up when revved.

That was when engine was a operating temperature, was it?

 

I wonder if the water pump might have lost most of its talent for pumping somehow?

Any chance the coolant mixture has become too weak through topping up with just water, and you've had some ice form in the system recently, that has then damaged impeller blades of the pump?

 

Edited 8 February by Breezy_Pete
sp

[Gaborr]

Yeah the cold radiator and lower hose combined with the pressurised upper hose sure sounds like there is a blockage in the radiator.

 

I'm unsure in what fashion would the pump fail. I was thinking that the temp going down when the engine is revved could be due to the impeller being able to spin up on the shaft.  But thinking about it now it could also be that the water is now able to flow past the blockage with the increased rpm?

 

Im fairly certain water didn't freeze as I haven't topped it up by that much.

 

[Alasdair1]

A blocked rad wouldnt create bubbles. Could be a crack in the head. Had similar symptoms in an old Toyota. Tiny crack between exhaust valve and inlet valve but because the combustion pressure is higher it forces  exhaust gas into the coolant and eventually causes air lock in heater matrix or elsewhere and temp would rise. If you revved it it seemed to clear the airlock and was ok for a while. Eventually airlock gets so bad that it first heater stopped working and then would overheat. Could also be the water pump thats drawing in air as thats a lot of bubbles in the coolant. I would have thought you would have seen a leak from the pump though but nothing surprises me anymore with cars. The coolant may be being forced out via the expansion cap and being replaced with air/exhaust which is trapped in the system somewhere. If its a cracked head  I used K seal and it cured it for a while. Theres also steelhead? which I think may be better.

[Gaborr]

39 minutes ago, Alasdair1 said:

A blocked rad wouldnt create bubbles. Could be a crack in the head. Had similar symptoms in an old Toyota. Tiny crack between exhaust valve and inlet valve but because the combustion pressure is higher it forces  exhaust gas into the coolant and eventually causes air lock in heater matrix or elsewhere and temp would rise. If you revved it it seemed to clear the airlock and was ok for a while. Eventually airlock gets so bad that it first heater stopped working and then would overheat. Could also be the water pump thats drawing in air as thats a lot of bubbles in the coolant. I would have thought you would have seen a leak from the pump though but nothing surprises me anymore with cars. The coolant may be being forced out via the expansion cap and being replaced with air/exhaust which is trapped in the system somewhere. If its a cracked head  I used K seal and it cured it for a while. Theres also steelhead? which I think may be better.

 

Yeah that makes sense that a blockage wouldn't cause bubbling but I would assume if combustion gases leak into the coolant lines then once the car cools down the expansion cap would release the excess pressure once opened but it doesn't seem to do that.

 

Unless the built up pressure leaks back into the combustion chamber? I'm not sure if that'd be a possibility.

 

[Alasdair1]

On my toyota I used to get a small amount of coolant leaking back into the cylinder once the engine was stopped but once cool the crack would seal itself. To begin with there was a little white smoke but very noticeable. When cold it looked like normal exhaust on a cold day. Eventually it got so bad it hydraulicked the engine. The extra pressure from the exhaust gases may be forcing the coolant out of the expansion hose past the cap and leaving air/exhaust airlock behind. It may even cause a slight vaccum? My coolant did this but the level remained fairly constant. Is the oil cap clean and not emulsified? Mine was always fine as the coolant was leaking into the cylinder and not the oil ways.I would see if a local garage can check if the bubbles are exhaust gases or just air. Hope you get it sorted

Alasdair

[Gaborr]

So I've done a bit more troubleshooting about this issue.

Had a look inside the cylinders to see if any coolant can make it's way into the combustion chamber. I've done so using a not so great endoscope, despite the not so great picture quality I can't really see any coolant in there.

Cylinder 1 - Cylinder 2 - Cylinder 3
https://imgur.com/XgXQSR4
Also performed a coolant gas test. This one was a bit inconclusive. The liquid turned green but not yellow, which basically means either there is a small leak, or it was exposed to heat. Fluid turned green at around 5 mins, which is supposed to be the max length for the test. So I'll have to redo this test this week.
Initially I thought that the the way the fluid is being pushed out is due to the exhaust gas coming through it. At the same time if this much exhaust gas is coming through I would think that the test would be a conclusive fail, so this is most likely just air?

Checked the thermostat as well and it opened at the correct temperature.

Another interesting behaviour I've noticed is when I was bleeding the car, the temp wouldn't raise when idling, only when the engine was revved, and then when I stopped revving it fall back down.
Should the car warm up just by idling?

 

Lastly when I was driving around, the teperature would go up slightly from the middle, then it would drop down, then again slighlty go up. It was unrelated to load, it wasn't overheating more when I was accelarating more.
I'll do another coolant gas test and if it comes back negative I'll take the water pump out to see if it's damaged, and try to bleed out any air that is in the system.
 

[Alasdair1]

Cars should eventually warm up to normal temp when idling unless the thermostat is jammed. If theres no coolant in cylinders or exhaust gas in coolant and the bubbles are air then I would think it might be the waterpump. I would check and replace it and see if it helps. It may be that the pump seal is drawing in air or the impeller has failed. Cant think of anywhere else air could be getting into the system unless the pump isn't strong enough to purge it but where did the air come from?? Check the drive belt for the pump as well.

Alasdair