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Old 08-09-2014   #1
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Unhappy Plastic coolant hose fitting broke off

My wife called to say to say the water temp alarm had gone off in her 2010 Fiat 500 1.2 Lounge.
I went to the car and found that a PLASTIC fitting in the engine block to which a coolant hose is attached had sheared off, dumping all the coolant water on the road.
It had sheared and left the threaded part in the block.
Maybe it was over tightened when the car was built, but why on earth would they use plastic for a fitting to the (very hot) engine block?
Has this happened to anyone else? I searched this forum and found no other instances, but I feel it is only a matter of time with any car using this part!

If you have had this problem, how did you get the threaded part back out?
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Old 08-09-2014   #2
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Re: Plastic coolant hose fitting broke off

Modern plastics are so advanced that the days of plastic automatically being cheap crap are gone. "Hot" engine blocks don't bother the correctly specified plastic, as evidenced by the rarity of this problem. One of those things that's crappy when it happens but also just "one of those things" on a 4-5 year old cheaply built car.

Assuming it's only a small hose that's come off, stud extractor or reverse tap to get it out.

I'd be more worried about any other damage that might have happened if it was driven for long afterwards.
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Old 09-09-2014   #3
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Re: Plastic coolant hose fitting broke off

I have since been to the Fiat dealer and it seems I have to replace the entire thermostat housing as you cannot get the plastic fitting on its own, but at only 30 that is probably the best route.
Zanes: I take your point about modern engineering plastics being much better these days, but they still change properties under temperature. If it is threaded to the metal housing it will be under permanent tension, and any defects in the radius to the flange face will cause stress cracking to spread. It may well be that it is not in fact threaded any way, so I will investigate & report back! Perhaps they have been more clever than I thought, but I wouldn't mind betting that in about 3 years they will be falling off all over the place ... I hope I am wrong! As you say, the consequences of the failure can be much higher, and so I would much rather have seen a better design. But there again, I expect a BMW thermostat housing would have cost me a lot more!
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Old 09-09-2014   #4
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Re: Plastic coolant hose fitting broke off

Quote Originally Posted by KevinM View Post
I have since been to the Fiat dealer and it seems I have to replace the entire thermostat housing as you cannot get the plastic fitting on its own, but at only 30 that is probably the best route.
Zanes: I take your point about modern engineering plastics being much better these days, but they still change properties under temperature. If it is threaded to the metal housing it will be under permanent tension, and any defects in the radius to the flange face will cause stress cracking to spread. It may well be that it is not in fact threaded any way, so I will investigate & report back! Perhaps they have been more clever than I thought, but I wouldn't mind betting that in about 3 years they will be falling off all over the place ... I hope I am wrong! As you say, the consequences of the failure can be much higher, and so I would much rather have seen a better design. But there again, I expect a BMW thermostat housing would have cost me a lot more!

<senses someone knows more about material engineering than I do> In fairness, it does seem a little cheap and surprising that it's not just cast into the thermostat housing- I guess the shapes involved mean that's not possible. Wouldn't the same issue wrt spreading cracks be present in metal (I guess cast alu?), and possibly worse? I wouldn't be surprised to learn that it's somehow bonded in TBH- why pay for machining two threads when a ring of decent adhesive will do the job.

Worth noting that the oldest 500s are now coming up seven years old and there haven't been many reports of this yet AFAIK and that the exact same engine is in pandas and puntos- older versions are in cars dating back decades. I still think it's "one of those things" and that you've been unlucky- given FIAT's past record it could be half arsed design/test though.

http://www.shop4parts.co.uk/?name=st...173&sku=183960
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Last edited by zanes; 09-09-2014 at 16:06.
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Old 09-09-2014   #5
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Re: Plastic coolant hose fitting broke off

Zanes: Thanks for the link to Shop4Parts. Interesting! I notice the photo on the link shows the fitting that broke as metal! I wonder if Fiat did some 'value engineering' and tried to save a few bob. ... and I wonder when the change was introduced. (2010?) Arrrgh!
I will post a pic in case someone has the same problem in future, or wants to check their car.
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Old 11-09-2014   #6
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Re: Plastic coolant hose fitting broke off

This is a photo of the replacement part. The black plastic fitting to the right broke at the metal interface and came right off.
This is the connection to the heater matrix, and when it comes off the water is pumped out of the car on to the road in only a few minutes, and could therefore be catastrophic if you don't stop the engine quickly. Fortunately my wife did so when she smelled the 'burning' before even the temp gauge topped out. So far the engine is still running fine. I think I got away with it, but I think Fiat 500 owners should be aware of this weakness.

I hope this helps someone.
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Old 11-09-2014   #7
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Re: Plastic coolant hose fitting broke off

Interesting that the plastic fitting is indeed screwed in, judging from the flats cast into it.

I wonder if the coolant "alarm" is clever enough to note the rapid fall in temperature (presuming the coolant sensor is the brass fitting with a connector) when the coolant level dropped past the sensor and exposed it to air.

Your wife is to be commended on her rapid actions which probably saved the engine from serious damage.
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Old 11-09-2014   #8
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Re: Plastic coolant hose fitting broke off

You raise a good point about the sensor. I don't think the alarm is particularly clever. When I first tested it after the breakdown the gauge fluctuated wildly, and the "Stop the engine" message came on & then went off again. I think the problem is that the breakage is very near the sender unit, and in 'spilling' mode the water does not always flow evenly over the sensor. Another risk point! It would be better if the failure message latched on for say 30 seconds.
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Old 11-09-2014   #9
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Re: Plastic coolant hose fitting broke off

Quote Originally Posted by KevinM View Post
The black plastic fitting to the right broke at the metal interface and came right off......I think I got away with it, but I think Fiat 500 owners should be aware of this weakness.
I hope this helps someone.
Thanks for the effort you have put in to draw attention to the problem you had.

Not that it makes much difference, but did you go for a genuine Fiat part in the end, or an aftermarket part? I only ask because I generally, for the most part, buy genuine marque parts, but I do have exceptions to this rule, especially when I know an aftermarket part has been produced to a standard exceeding the factory fit stuff.
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Old 11-09-2014   #10
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Re: Plastic coolant hose fitting broke off

Quote Originally Posted by frupi View Post
Thanks for the effort you have put in to draw attention to the problem you had.

Not that it makes much difference, but did you go for a genuine Fiat part in the end, or an aftermarket part? I only ask because I generally, for the most part, buy genuine marque parts, but I do have exceptions to this rule, especially when I know an aftermarket part has been produced to a standard exceeding the factory fit stuff.
I usually use reverse logic & buy aftermarket parts - if the OEM component failed prematurely, it's time to try something else.

This looks like yet another example of Fiat penny pinching; assuming that plastic stub is threaded, I'd be sorely tempted to seek out a lathe & a piece of hex brass bar & repair the old housing.

I reckon a small engineering shop could knock out a batch of 50 or so for around a tenner apiece - now that would be a useful group buy.
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Last edited by jrkitching; 11-09-2014 at 18:37.
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Old 11-09-2014   #11
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Re: Plastic coolant hose fitting broke off

Quote Originally Posted by jrkitching View Post
I usually use reverse logic & buy aftermarket parts - if the OEM component failed prematurely, it's time to try something else.
Agreed, and that is why I'll choose Meyle for instance on replacement drop links, or Bilstein for shocks. But there is just some stuff I won't take an aftermarket risk on. Oil filters for instance, and this has just cropped up in another thread, I haven't used an aftermarket oil filter in any car I've owned in the last 15 years because sometimes you just have no idea quite what you are going to get quality wise. Air/pollen filters, not really an issue in my book. Worst aftermarket purchase I ever made, were some HT leads for my old Nissan which I bought from a high street motor factors. The leads melted onto the spark plugs and I had a helluva job getting the beggars out! They cost me 20 and I never did get the money back on them. I ended up having to buy genuine Nissan leads from a dealership for 54. Never had a problem again.
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Old 11-09-2014   #12
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Re: Plastic coolant hose fitting broke off

Quote Originally Posted by frupi View Post
...there is just some stuff I won't take an aftermarket risk on. Oil filters for instance, and this has just cropped up in another thread, I haven't used an aftermarket oil filter in any car I've owned in the last 15 years because sometimes you just have no idea quite what you are going to get quality wise.
.

Like yourself, I'd always buy an OEM oil filter - the risk of damaging your engine just isn't worth saving a few pennies.

There was another thread on here just a few days ago when some poor chap bought an aftermarket oil filter for a TA & came close to wrecking his engine.
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Old 11-09-2014   #13
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Re: Plastic coolant hose fitting broke off

I'd buy aftermarket if it was something like Mahle or Bosch or some brand that is well respected, otherwise no.
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Old 11-09-2014   #14
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Re: Plastic coolant hose fitting broke off

Quote Originally Posted by 306maxi View Post
I'd buy aftermarket if it was something like Mahle or Bosch or some brand that is well respected, otherwise no.
Yup agreed and to be fair when you realise that Mann for instance are actually the filter supplier for many marques, then there's definitely no problem with a company as well known as them. I recently bought several genuine Fiat boxed oil filters for my Saab that clearly have the Mann logo on the top of the filter.
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Old 11-09-2014   #15
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Re: Plastic coolant hose fitting broke off

Yup, I know what you were trying to say though, why buy from a company that isn't well known?
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