General Temp Gauge

[jim whitehead]

When driving down hill I.E with foot off the gas, the temp gauge drops a little from normal temp to about two noches below, when I put foot on gas again temp appears to go back to normal.

It does this after car has reached normal temp not experiencing any other problems. Fiat Punto 1.2 8V. 114 000 miles on clock.

Any ideas ?

 

[homeward]

I'd suspect a small airlock, somewhere in the cooling system. Have a look at this guide, and see if it's any use....

Good luck...!

 

[fingers99]

Then again, foot off the gas, but car moving -- the engine is producing little power (and therefore little waste heat) but the radiator is getting cooling airflow. As soon as you hit the throttle again, the engine produces more power (or does more work) and produces more waste heat.

You might like to think of the situation of a cyclist doing the same thing.

 

[homeward]

Then again, foot off the gas, but car moving -- the engine is producing little power (and therefore little waste heat) but the radiator is getting cooling airflow. As soon as you hit the throttle again, the engine produces more power (or does more work) and produces more waste heat.

You might like to think of the situation of a cyclist doing the same thing.

I actually love the logic of this... -- and it makes a lot of sense to me... -- just that, since I fitted a new thermostat, and bled the system incredibly thoroughly: once warmed up, the temperature gauge remains pretty much rock steady, whatever the situation (including that of the OP's...).

 

[Brendan W]

I would be thinking the stat is sticking part open. Not enough to stop it warming up in a reasonable time but not able to react when the gas comes off.
I would also check that the alternator is producing 14+ volts at idle and is regulated as revs are increased. Temp senders are voltmeters at the end of the day.

 

[fingers99]

Changing the stat wouldn't be a bad idea anyway -- just make sure it's a branded, decent, one. Halfords, or one from Fluffy the Impaler or Shop4Parts or FIAT. There are a fair few dodgy ones out there.

The voltage thing is a possibility, but never something I've encountered on an Italian car -- or anything post 60s.

 

[Brendan W]

Voltage a long shot as I would expect ecus to have an internally regulated supply for sensors rather than relying on the offerings from the charging set up - but you never know.

 

[Ziggy122]

sounds like to a sticky stat all round to me

its only going to get worse tho

ziggy

 

[jim whitehead]

Thanks for all the advice, is it an easy job replace the stat? what sought of price I am I looking at?

Interestingly the alternator belt is a little loose so it could be that?

Any idea how long an Alternator would last on a Punto, bearing in mind it's done 114000 miles?

 

[Brendan W]

On paper the stat is easy but the screws can be corroded in the head to the extent that they snap off. Good idea to plus gas them a day or so before the big event. Reckon a good stat is around the £25 mark tops plus a bit for the coolant.
Might be worth wiggling the sender wires to see if you can reproduce the change in needle position. The motor will rock a bit going to overrun and if a wire is not free to go with it, it could be pulling a bit on a plug.
If you do disconnect the sensor with the motor running you can expect, depending on the model, the fan to come on and the eml lamp which can then stay lit for the next two or three cycles until the ecu is convinced it really is reattached.

 

[Ziggy122]

If the belt is loose - 3 bolts - slacken - Tension belt via alternator body - Tighten Job done

if the belts cracked or shiny = new belt needed

the alternator could last years or months
Check the alternator performance by doing the following test with a Multi-meter set to 20v DC over battery terminals

Engine off - 12v - 12.6v
Engine Running - 13.5 to 14.3v - if the battery was flat 13.5v is okay as its still recharging, but if the battery is new i'd be testing on a regular basis
Engine Under Heavy Demand - Switch all Fans, lights, heaters, Plug your phone in to charge etc etc - then See what voltage you get

Personally i know that the voltage often drops alot - as the punto has a small battery and alternator
i've seen loads drop to 11.8v - Few revs and its up at 13v +
13v+ is ideal really - but at idle the revs aren't often enough to power everything

Engine under heavy demand + 2k revs = Should show a stronger output around 13.5v

Ziggy

 

[jim whitehead]

thanks for your help Brendan