Overheating...

[tmf123]

mine definitely overheating. Aside the fact it is starting to throw oil through every gasket, the oil light starts to flicker on at idle because the oil becomes so thin with heat.

Still haven't had a chance to drive it, but will do so over the weekend....

[drcdb15]

That's interesting. I presume he simply placed a thermocouple against different areas of the engine. Obviously you'd want parity between the two sides, so for example you'd want the cylinder head on each side to be roughly the same. You'll never get them identical but I'd imagine within say 5 degrees of each other.  But to say the absolute value of the temperature is much higher than it should be suggests that somewhere Fiat must publish this data.

I don't recall ever having seen such temperature data, either for any air-cooled Fiat or for any other air cooled engine like the VW. Haven't got my Haynes manual to hand to check, but is this data readily available and I've just never noticed it?

Reading around this issue, I've just found this item which suggests that if an air-cooled engine overheats it's simply because it is not being cooled enough: http://www.liquidcooledairpower.com/lc-topendheat.shtml
as opposed to something being "wrong", such as timing or fuel supply.

Running too hot leads to issues with the exhaust valves and seats, and the differential heat/cool cycles may already have caused damage such as cracking the head - you'll see that some service schedules recommended REPLACING the cylinder head as a SERVICE item!

One obvious if somewhat painful option might be to fit a known good cylinder head.

Another explanation may be that the engine isn't getting its full ration of cooling air, either because of some constriction or blockage causing air starvation as I suggested previously, or perhaps because the fan output is degraded - are there any broken fan blades? Or could the fan rotor be slipping on its spindle? Or is there any build up of grot in the cylinder head ducting or finning which is hindering the air flow? Or are there any gaps in the ducting allowing cooling air to by-pass the engine or cylinder head?

[drcdb15]

mine definitely overheating. Aside the fact it is starting to throw oil through every gasket, the oil light starts to flicker on at idle because the oil becomes so thin with heat.

Apart from the heat removed by the exhaust gases themselves, the primary cooling is generally the oil underneath the piston crown - depends on the exact geometry of course, and a lot of heat gets away through the metal of the head, but the piston crown is typically a lot thinner than the head casting, plus the oil is continually flowing both under the crown and all around the cylinder walls outside the piston skirt.

So I am wondering whether in your case the heat is leading to thin oil, or perhaps lack of sufficient oil is leading to too much heat?

Have you checked that the oil filter is cleaned out, and that the oil pump is working properly? Frequently the oil filter is either not cleaned or not cleaned properly due to its location and type, so build up of residues here would impede oil circulation. Also a worn oil pump will not put out sufficient flow. It might be worth checking that the the oil system is up to scratch before worrying about other possible problems.

[Bar Vitelli]

Well, thanks to Mark and some gadgets we think we've found the root cause which is something that Rusty called out in one of his earlier replies.  Whilst overheating may have been one of the original issues which we probably fixed without realising the latest diagnosis is that it is probably an electrical issue linked to the Dynamo not charging and/or the regulator not working.

We had the car hooked up to Marks mega-battery (because mine had gone flat) and the engine worked and sounded like a dream. After some time the GEN light came on and shortly after the engine cut out. Marks gadgets and experience helped us identify voltage issues which with phone a friend to Pete126 and Mark's auto-electrician friend pointed the finger to the Dynamo brushes needing replacing.

I'm going to order some of these and with Mark's help fit them. Hopefully that will sort it. If it does not then the regulator will be the next thing to replace.  Please shout out if anyone knows where to get one cheap.

Should get all this done within the next week or so and will post a further update. Thanks for everyone's help and support, can't wait to see Mrs BVs car working in time for a summer convoy!

 

[Da Londo]

Great to hear the problem is found, Fiat126fan.sk has the regulator for €18 and Fiat500ricambi.nl for €35 but I think you can find em in UK for similar price.

[Bar Vitelli]

Thanks, Da Londo, much appreciated! 

[Skippy]

I too have read this thread with interest, I'm glad you've finally fixed the problem.
We have a Bis which has never had any overheating issues but I also have a Triumph Herald Coupé which had overheating issues for years. In the end I switched to super unleaded petrol (higher octane and low/no ethanol), advanced the ignition until it pinked and backed it off till it just stopped. No more overheating.
Someone mentioned that unleaded burns hotter than 4 star which is true. Being lower octane we have to retard the ignition. The combination of the 2 can cause overheating, especially if you're running with higher compression (perhaps the head has been skimmed.
Anyone having overheating issues should give this a go.

[Bar Vitelli]

Well, another marathon session, we changed the Dynamo brushes which was actually really interesting but did not sort it but did eliminate one other problem leaving the voltage regulator as prime suspect. We swapped it with one from one of my working cars and it is now charging much more correctly.

The plan now is to charge up the battery overnight and take it for a drive tomorrow. Very confident that it is now sorted but the drive tomorrow should prove it. If not the car will be on eBay with no reserve!

Massive thanks to everyone for their help and ideas and especially to Mark (and his gadgets and his auto-electrician friend!) and Chris!

 

[1973/126]

 So Garry, how did it go? Just so I know if to keep an eye on eBay for an early 126

[Bar Vitelli]

Still not working...

I'm really not sure what else there is to do.   

We've fixed lots of things along the way which will make it super if it ever does get fixed and for the short time when it does work it sounds better than any of my other cars.

It feels like we are back where we start with lots of stuff eliminate along the way and a better understanding of what is happening but not an absolute understanding of what is causing it.

It starts, runs super for a bit, after about 10 minutes the engine starts to shudder, then the red GEN light comes on and then it cuts out. When it cuts out it is very hot and takes about 10 minutes to cool, down before it will start again and repeat it all over again.

Mark has been amazing (as has Chris) and has promised to come back with some more gadgets to compare temperatures at different points in the engine to see if that will give us some clues.  I think it will show that the right hand side of the engine is significantly (maybe 100 degrees) hotter than it should be but not sure why.  If we can figure out what's causing it we will have cracked it. If not, Ladislav will be getting an eBay bargain.  Which will serve me right as I originally outbid him on eBay for this car several years ago! 

[Da Londo]

Someone mentioned the cooling fins from the cylinders, have you ever taken of the cooling plates to see if air can pass around the engine?

[drcdb15]

I mentioned cooling with both air and oil previously. Obviously if there *was* any electrical issue it has been sorted, since the engine starts and runs OK. The GEN light coming on sounds like a red herring, because as the engine starts to stall the revs drop and the light would come on anyway.

There are two questions, it seems to me: why does one side get hotter than the other, and why does getting hot stop the engine?

If an engine gets too hot, it doesn't just stop only to be startable again when it's cooled, it keeps running getting hotter and hotter until it seizes. So there are in my view TWO problems - one is that one side is getting too hot (so check blocked cooling airways, and blocked oilways - sorry, but an engine strip might be in order); the other is that something is breaking down when it is getting too hot (so this might well be an electrical item such as the coil - however, this issue can be 'solved' by not letting the engine get too hot in the first place. So that brings us back to a blocked airway or a blocked oil way.

There is one other way of looking at this: not enough cooling in one side might also be caused not by a blockage on *that* side, but by a massive leak on the *other* side.

For both oil and air, the cooling fluid comes from a common source (pump and fan respectively). It is then split into two halves, one to each cylinder. If one of those halves has a huge leak in it, allowing the fluid to escape, the *other* side will not get its full share of the fluid, and hence not get its full share of the cooling.

[dadandlad]

At this moment in time I'm not convinced she is overheating and I have not seen anything to suggest  as such

There was definitely a charging issue as only 12.5 volts produced at high revs and now producing 14.5 volts

She has reasonable compression with both cylinders at 125psi so pretty consistent and not suggesting it has nipped up

The oil warning light does not come on when running so suggests no excessive thinning of oil

I have a few ideas to try and hoping to get my partner in crime to assist so we can watch a couple of multimeter's at the same time and two heads are better than one

Will keep you informed after next Fridays episode

[Rusty's Uncle]

I had what may have been a similar problem with my 500 and I changed everything plus bypassed components but never really got to the bottom of the problem but the thing that finally got rid of the problem was the fitting of electronic ignition. I could lend you one if you wanted to try it 

[Bar Vitelli]

Thanks, Rusty, that's very kind.

I've got one in my 500 so we could always use that if needed.

PS

Please PM me your address when you get chance, I might be doing a South to North road trip soon so would be great to stop by and say hello...