Not sure where else to go for advice - 2 ltr twin cam proble

[hudsonhenry]

Guy

This ones probably a bit mundane but you have always given me some excellent advice in the past so here goes:

I'm hoping that you or one of the other forum members might be able to help me with the diagnosis of a problem a friend of mine is having with a 124 spider. The car is a US Import 2000cc injected one and has not been modified.

He discovered, shortly after buying it that the head gasket had gone. He had the head skimmed, replaced the gaskets and re-fitted it. When he re-started the car the temp gauge crept up to just past the 0 of the 190 on the gauge then flicked over to off the scale but the fan did not cut in at all.

He fitted a manual override to the fan and if this is switched on when the temperature hits 190 it will drop to around the 150 mark for as long as you leave it on. Switch the fan off and the temperature creeps up slowly to just beyond the 0 of the 190 mark then flicks over off the scale of the gauge.

So far he has:

Replaced all the sensors

Bled the system under pressure

Tested the fan sensor with fan connected in boiling water - fan came on

Had the radiator re- cored

Tested the gauge, an alternative gauge does exactly the same thing.

The Car does not seem to be running hot and he has sniff tested the system twice since changing the head gasket and pressurised the system to eliminate any air locks. He is now at a loss as to what to try next.

To me it looks like he has two issues, the first is the fan switch (the one on the bottom of the rad – is this the right switch for the fan?) which looks like the previous owner has badly re- wired. As I said, this was tested by putting the sensor in boiling water and was ok but there could be a dodgy connection. This could easily be sorted by re-wiring properly or by putting in an aftermarket temperature switch into the top hose to switch the fan.

The second problem seems to be the temperature sensor for the gauge, it seems to be acting as a switch once it gets to a certain temperature, could this be the wrong sensor fitted? Or should this be switching the fan or some emissions control device on? Any advice would be much welcome.

My engine knowledge is with aircooled Fiat 500 twins and more recently Fiat Fire engines and the cars owner knows his way around MGB engines very well but has never worked on a Fiat twin cam before so we could be missing something very obvious!

[robert kenney]

Guy

He fitted a manual override to the fan and if this is switched on when the temperature hits 190 it will drop to around the 150 mark for as long as you leave it on. Switch the fan off and the temperature creeps up slowly to just beyond the 0 of the 190 mark then flicks over off the scale of the gauge.

So far he has:

Replaced all the sensors

Bled the system under pressure

Tested the fan sensor with fan connected in boiling water - fan came on

Had the radiator re- cored

Tested the gauge, an alternative gauge does exactly the same thing.

The Car does not seem to be running hot and he has sniff tested the system twice since changing the head gasket and pressurised the system to eliminate any air locks. He is now at a loss as to what to try next.

To me it looks like he has two issues, the first is the fan switch (the one on the bottom of the rad – is this the right switch for the fan?) which looks like the previous owner has badly re- wired. As I said, this was tested by putting the sensor in boiling water and was ok but there could be a dodgy connection. This could easily be sorted by re-wiring properly or by putting in an aftermarket temperature switch into the top hose to switch the fan.

The second problem seems to be the temperature sensor for the gauge, it seems to be acting as a switch once it gets to a certain temperature, could this be the wrong sensor fitted? Or should this be switching the fan or some emissions control device on? Any advice would be much welcome.

My engine knowledge is with aircooled Fiat 500 twins and more recently Fiat Fire engines and the cars owner knows his way around MGB engines very well but has never worked on a Fiat twin cam before so we could be missing something very obvious!

First is to ask if you have the two way thermostat? they are easily hooked up wrong. I added a photo of a 78 124 with the "T" shaped two way thermostat. Don't know if the FI later models were the same in the US.

Second to the temp gauge seeming odd function, not really odd at all. The T/C 124 Fiats were with two temperature senders an a linear thermistor that drives the gauge through the normal 0 - 198 F range and a second sensor that acts as a switch to light the red temp warning light and cause a rapid full scale reading that I suppose is designed to let the driver know that YES the engine is truly hot. I can't say for sure whether or not all T/C based road cars were this way but
at least the ones I have seem have been.

Third This is also common based on how difficult the Spyders are to bleed. Some recommendations are to drill a small bleed hole (.063) in the thermostat so water and air can flow across the valve element aiding in bleeding air while filling with coolant.

Also add a T on the high heater hose that plumbs to the top of the cylinder head so air can be more easily removed while filling the cooling system. You can see in the attached photo the brass plug and T behind the distributor cap

I would suggest installing a mechanical capillary tube temperature gauge to verify the temp my guess is the engine is getting hot though.

Hope this helps

Robert

[MinorTC]

My Fiat 2.0-litre (carb-fed) twin cam also runs hot. Does anyone know the correct way round that the two-way thermostat should be fitted? Also, where to get hold of a temperature gauge that works with the temperature sender in the cylinder head?

Regards,
Maurice (Kent, UK)

[hudsonhenry]

Second to the temp gauge seeming odd function, not really odd at all. The T/C 124 Fiats were with two temperature senders an a linear thermistor that drives the gauge through the normal 0 - 198 F range and a second sensor that acts as a switch to light the red temp warning light and cause a rapid full scale reading that I suppose is designed to let the driver know that YES the engine is truly hot. I can't say for sure whether or not all T/C based road cars were this way but
at least the ones I have seem have been.

That's interesting as my first thought was that the sensor was working like a switch when it reached a certain temperature which would be at around 198 F. Is it normal for the gauge to flick over to maximum when the light goes on? I did not see a light come on when we tested the car. Is it possible that I have two warning light sensors or that the warning light sensor or wiring is shorting out causing the gauge sensor to flick off the scale?

I think the answer with the fan is to re-wire, when the fan is switched manually it takes the temperature from 190 down to about 150 quite quickly and will sit at 150 for as long as the car is running (stationary), switch the fan off and it creeps back up until 198 when it flicks off the gauge scale. It could be that once we get the fan switching on and off by itself it will never get hot enough for the gauge issue to raise its head. It has however confused us and i suspect that the car was sold on after somebody else messed around with it and failed to solve the fan switching problem and messed up the wiring in the process.

It does seem to be bled properly, it was done with an air powered pressure tester. You mention the T shaped two way thermostat, we think this had been fitted upside down as the picture in the manual showed it the other way to the way it was when he bought it. Which way is the correct way to hook it up?

Many thanks

Nigel

[robert kenney]

Is it normal for the gauge to flick over to maximum when the light goes on? I did not see a light come on when we tested the car. Is it possible that I have two warning light sensors or that the warning light sensor or wiring is shorting out causing the gauge sensor to flick off the scale?

I can only speak for pre EFI Spyder models. Is it possible that the light is out? I would think the FI system would have its own analogue temperature sensor and have only one temp switch for the sudden move up scale. Hope some one who knows for sure can add here.

It does seem to be bled properly, it was done with an air powered pressure tester. You mention the T shaped two way thermostat, we think this had been fitted upside down as the picture in the manual showed it the other way to the way it was when he bought it. Which way is the correct way to hook it up?

I am of the opinion that you have your thermostat upside down. Normal operating temp should be 180F +/-. You say if the fan is on it falls to 150F? I added my take of the coolant flow with the two way OEM thermostat. Sorry for my lack of graphics skill.

If the thermostat is rotated 180 degrees the water would flow through the radiator when cold and after the temp reached a level high enough for the wax pot to move the valve open the water would flow mainly through the bypass route,and the radiator and fan switch would never see over temperature water so never switch.

When the engine is cold or below normal temp and fan is off the bottom tank should remain basically cold but in the case of the inverted thermostat it would become warm as the engine warned up indicating coolant flow when it should be going through the bypass route.

Hope this helps

Robert

[miro-1980]

Gents,

Hot running engine was my top worry with both 131 2.0 and 124 spider CSO.

Now the worry is gone. Look at my experience. If this worked for me it will work for you as well.

First, you may want to look at these:

viewtopic.php?f=8&t=67&p=120&hilit=cooling#p120

viewtopic.php?f=13&t=1251

viewtopic.php?f=6&t=1810

Both my Fiats (131 and 124). Both are fitted with manual override switch - nice to have !

- 131 has twin Fiat fans and 124 is being fitted with a flat push fan in front of the radiator. this is to cut on the time the fan has to work to cool the engine down.
I have noticed that the engine get really hot it takes a real long time long time to cool it. My theory: by allowing the engine to get very hot you also allow all parts under the hood almost as hot. To cool down the engine you really need to cool all elements under the hood - not the engine alone and this takes time. (Just imagine how much cold running water you need to cool one hot hard boiled egg and how much to cool 5 hot hard boiled eggs? The logic is the same with the hot engine bay.)

Both engines were running quite hot around 100- 110C ( at the reading of 110 C the fans would switch on, getting the temperature to just around 100C. I have tried everything and nothing seemed to ho help.

1/ I went for lower temperature thermostat ( from standard 85 C to 79C. I will switch to one with 71C rating later this month

2/ made sure the coolant solution is strong enough and there are no air bobbles trapped in the block.

3/ properly tuned and timed engine (the timing was retarded and this made the problem even worse)

Finally I i changed from 87/92C I had to an old fan temperature fan switch I found in the garage rated 77/82 C. (I am actually thinking of going still lower 78/65 C.)

The last change was the one which made the real difference. Currently I can drive for hours at 140 km/h with temperature at 90 C constant. I do not even look at the gauge any more .... No worries!

Note : there are many factors which may contribute to high running temperature of your engine (some related to engine emitting too much heat and others by inefficiencies of the cooling system, and still other by other elements like hot brakes, hot exhaust. poor ventilation of under-the-hood area.) From my experience start with the basics : low temperature thermostat and low temperature fan switch on a properly tuned engine, proper spark plugs, proper grade of fuel... If this does not work - look for problems elsewhere.

Miro :

PS: With the new engine I am switching to a low rated in head thermostat from GC.

[hudsonhenry]

I am of the opinion that you have your thermostat upside down.

Robert

Well done that man... When the thermostat was removed it was marked to ensure that it went back in the exact same position, it did not occur to us that the previous owner had fitted it upside down in the first place! but I guess looking at the other bodges in the engine bay... That would explain why it was sold with a blown head gasket.

The whole system is working perfectly now, many thanks for the advice Robert it is very much appreciated.

Nigel

[Guy Croft]

I missed this one being away for a week but I must say how impressed I am with the calibre of this thread.

Well done all,

G

[robert kenney]

I am of the opinion that you have your thermostat upside down.

Robert

Well done that man... When the thermostat was removed it was marked to ensure that it went back in the exact same position, it did not occur to us that the previous owner had fitted it upside down in the first place! but I guess looking at the other bodges in the engine bay... That would explain why it was sold with a blown head gasket.

The whole system is working perfectly now, many thanks for the advice Robert it is very much appreciated.

Nigel

Nigel,
Thanks' so much for the update just happy to help!!

Robert