Technical Coolant loss - head gasket?

[spleenharvester]

I've been through the ringer with the coolant system on this car - 2011 Fiat 500 1.2 312 with 169A4000 engine. I have replaced basically all hoses and clamps in front of the firewall, the water pump as part of a timing belt change, the coolant pipe attached to the engine etc. All bled properly every time a change was made. I've inspected everything down to the water pump gasket to try and find any leaks and I'm finding nothing. No signs of dampness behind the firewall anywhere. There is a very small leak on pressure test when pumped up to 1.4 bar (like loss of 0.1 bar after about 15-30 mins?) but I cannot see or hear any coolant bubbling.

The issue is the car basically dumps coolant down to about 3cm below the minimum level on a short journey before stabilising, which is roughly at water pump height. Even filling it right up to the very top - it still dumps easily a half litre of coolant somewhere. After a while of running low the heater core seems to airlock and it stops blowing hot air out into the cabin, and very occasionally will throw an overheat warning on the dash, but this seems to be sporadic. You'd have thought it would be forming a puddle underneath the car or something with the amount it's losing but there just aren't any signs of anything at all.

The only things I can really think of are (a) the head gasket - which doesn't really make much sense as there's no oil in the coolant and the car is running fine aside from this? - and (b) the radiator, possibly if there's a small crack in the front of the rad it's draining into the bumper area and may not be immediately visible. But I feel like I have ruled out pretty much everything else, other than a leak in the cabin, and I feel like we'd notice half a litre of coolant draining into the cabin.

Has anyone encountered this before?

 

[puntodeltathema]

They tend to get air in the heater circuit (as you've experienced). Assume you have been filling it correctly (after having the system apart) - undo both bleed screws, fill until coolant comes out of the radiator screw, replace that, keep filling until coolant comes out of the heater hose screw, replace. At this point the level in the tank may be well over max but if you then run it up to temp (take it up to 3000rpm for 20-30 secs every now and then) and let it cool it should stabilise within the MIN-MAX range, perhaps fully after a run or two.

If that doesn't work - is it producing a lot of steam? These engines don't tend to put water in the oil if the head gasket goes, but they will draw coolant into a combustion chamber (and may still run OK, at least for a while).

 

[spleenharvester]

They tend to get air in the heater circuit (as you've experienced). Assume you have been filling it correctly (after having the system apart) - undo both bleed screws, fill until coolant comes out of the radiator screw, replace that, keep filling until coolant comes out of the heater hose screw, replace. At this point the level in the tank may be well over max but if you then run it up to temp (take it up to 3000rpm for 20-30 secs every now and then) and let it cool it should stabilise within the MIN-MAX range, perhaps fully after a run or two.

If that doesn't work - is it producing a lot of steam? These engines don't tend to put water in the oil if the head gasket goes, but they will draw coolant into a combustion chamber (and may still run OK, at least for a while).

Yeah that's been my method so far - fill right the way up to the brim and then bleed, repeat after short journeys. But I must've put in about 3 liters so far so I'm pretty sure it is losing it somewhere and not just displacing air. No noticeable amount of steam.

I think I am going to fill to the brim again, pressurise with leak tester, take the bumper off and just get a really close look at this rad. If nothing shows up then I guess it's time for a leakdown test?

 

[GettinBetter]

Thats what happened to me during my trip around Europe. I thought it was the Expansion tank leaking, but when I cut the frazled end of the pipe and stopped the pinkish residue from accumuIating, it was still leaking. It was early summer so I also had the aircon on full blast, so it was difficult to tell if the water underneath was from the rad or aircon.
I ended putting some 'Radiator Sealant' in it, and it's been fine ever since, and that was May '24.

 

[spleenharvester]

I think I have found the leak - the coolant pipe and rubber fitting which I replaced in Feb 2024 at the point where it meets the engine block/water pump. I say think because it seems to be leaking very sporadically - when I first pressurised this time it was dripping under the car, but then it stopped and wiggling the pipe hasn't started it again. I lubricated the rubber fitting with something, I can't remember what, so maybe that's blocking it. It also fits with the height that the coolant level keeps dropping to.

I remember at the time I had trouble finding a good source, there are no OEM parts available that I can see, and I had issues fitting this one as the bracket with the screw hole was off by about 5mm. I can't really think of a solution other than trying to replace that rubber fitting again separately.

(E: It looks like you can get the genuine part for £80, pipe and seal - eye watering but if it solves the problem I'm game)

 

[spleenharvester]

Ok I'm having a bit of trouble finding the correct replacement. There seems to be 55245750, which has a purple seal, and 55185422, which has a black seal. An ebay seller has said you need to replace like-for-like. Problem is I don't know what this car had on it originally, it has the black seal now, but given it's leaking I'm not entirely convinced it's the right one. Anyone know of a way to check?

 

[Mike1alike]

I can recommend you a good seal.
I replaced that pipe on my Punto and noticed coolant leaking there in short time. The rubber that came with pipe was just that, rubber and it started leaking very soon. Original seal there was 3 layers rubber-thin metal-rubber. I found this one is exactly the same ELRING 685.350. I put that in August 2024 and no leaks since.

 

[spleenharvester]

I can recommend you a good seal.
I replaced that pipe on my Punto and noticed coolant leaking there in short time. The rubber that came with pipe was just that, rubber and it started leaking very soon. Original seal there was 3 layers rubber-thin metal-rubber. I found this one is exactly the same ELRING 685.350. I put that in August 2024 and no leaks since.

Thanks, the 685.350 was what came up in my searches too, this separate part for the purple seal thing is just confusing me. I will try it.

 

[Mike1alike]

And considering the big amount of coolant you lost, be aware the head gasket might have gotten damaged. It is sensible to overheating and running the engine low on coolant gets it overheated.
And oil in coolant or other way around is not a must for blown HG. That happens only when gasket is blown between cooling/lubrication channels. But gasket can blow between cooling channel and cylinder and then coolant enters combustion chamber and it's steamed blown away through exhaust. Normally, there is high pressure on cooling system when that happens because leak goes the other way around too and compression is lost to cooling system.
Wish you the head gasket is fine on yours.

 

[spleenharvester]

Can't recommend the 685.350 unfortunately, it needed a ton of hammering to get it on and that basically destroyed the end of the seal. I am going to order the genuine part with the seal already pre fitted. It's currently 55245750, apparently this replaced the older part with the black seal...

 

[Mike1alike]

Can't recommend the 685.350 unfortunately, it needed a ton of hammering to get it on and that basically destroyed the end of the seal.

Well... putting a drip of oil on seal before installing... priceless!
There are things money can't buy...

 

[spleenharvester]

Well... putting a drip of oil on seal before installing... priceless!
There are things money can't buy...

View attachment 483958

Tried that - damn thing just wouldn't go on at all, it was as if the metal ring was slightly too tight. I've bodged it for now and hopefully my genuine OE part will arrive soon.

 

[Mike1alike]

Tried that - damn thing just wouldn't go on at all, it was as if the metal ring was slightly too tight.

Is the engine block side clean, no gasket debris stucked or anything? Where pipe goes in.

 

[spleenharvester]

Is the engine block side clean, no gasket debris stucked or anything? Where pipe goes in.

It wasn't the engine block side that was the issue, it was getting the seal onto the pipe itself that was the problem. Once I had it most of the way on (which is where it currently sits) it went into the block no trouble.

 

[Mike1alike]

It wasn't the engine block side that was the issue, it was getting the seal onto the pipe itself that was the problem.

Hmmm... I wouldn't have thought that is even possible. Was it new pipe or the old one?

 

[spleenharvester]

Hmmm... I wouldn't have thought that is even possible. Was it new pipe or the old one?

Old pipe, but it was a non-OE pipe replaced a year or two ago so maybe the fitting isn't quite right. Part of the reason I've ordered the full replacement pipe + seal prefitted.

 

[spleenharvester]

Replaced with the OEM part today and it fits like a glove with practically no force needed, no more leaks. Shout out to Fiat Workshop for getting a replacement pipe to me within 24 hours, saved our Easter plans.

The part was 55245750, which Fiat Workshop say replaced 55185422. Club500Italia seem to think these aren't interchangeable and Fiat Workshop have "2012 onwards" listed on their site, but it looks like they are and 55245750 fits perfectly in my 2011 model.

 

[spleenharvester]

Car just got back from a 250 mile round trip. Coolant is still above the min level! It previously couldn't do 20 miles without losing most of it so a huge improvement. I am hoping the ~200mL or so loss in the expansion tank is just from air shifting around, but I put a UV tracer in there to be on the safe side and I can't see any leak. It's doing another big round trip tomorrow so we'll see when it gets back.

 

[Mike1alike]

Car just got back from a 250 mile round trip. Coolant is still above the min level! It previously couldn't do 20 miles without losing most of it so a huge improvement. I am hoping the ~200mL or so loss in the expansion tank is just from air shifting around, but I put a UV tracer in there to be on the safe side and I can't see any leak. It's doing another big round trip tomorrow so we'll see when it gets back.

Yes, it very well be from air trapped in the system, that got to expansion tank/radiator filler while engine was running. Top it up and watch the levels. Safe trips!

 

[spleenharvester]

Second trip today, no loss of coolant at all so hopefully that is the end of it! I think I have put about 4.5L in in total.

Slightly amazed the head gasket hasn't blown, it's routinely been running on about a liter of coolant for the past several months