Erractic Engine Temp - Alfa Romeo Forum
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Erractic Engine Temp

Hello. Anyone know what this is?

I start my car from cold, the temp rises slowly until it reaches very close to the top of the guage then it suddenly drops right down to about 60deg in a matter of seconds.

Im thinking its the thermostat but after reading other posts (not with the same problem but similar) it could either be water pump or rad.
The rad does seem to be corroding incidently around the bottom.

Thanks for your help.
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Re: Erractic Engine Temp

Could be a malfunctioning thermostat, sticking maybe?:
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Re: Erractic Engine Temp

If you can see rad corrosion then it will be a lot worse than it looks.

However, what you describe is normal for this time of year, if a little more exaggerated on your car, possibly a sticky thermostat as ZF says, but it is working ok. The temp drop is caused by your thermostat opening. The temp sensor is right next to the thermostat opening so it is sensing a sudden rush of cold water.

So long as after this the temp rises up to normal and stays there with only minor fluctuations then everything is fine - although start to think about changing that rad.
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Re: Erractic Engine Temp

Bring back AC wax-stats, says I? The one on my nineteen year old dent collector, is about 19yrs. old! No history of it being replaced in the past.: Eh! I'm so repetitive!! Half a' Kip!
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Re: Erractic Engine Temp

The corrosion on the rad isn't rust or anything its the small zig-zag parts of the rad that are falling off to the touch (just to be clear) Have already started the replacement ball rolling. Funny tho, one thing goes wrong with the car and once you take a good long look you see a few more.
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Re: Erractic Engine Temp

Sounds like the thermostat. If it's working properly the temperature should just rise steadily to the normal level & stay there. It shouldn't overshoot, as thermostat opening is proportional to temperature - there isn't a sudden change from closed to open.
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Re: Erractic Engine Temp

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Originally Posted by Dave Brand View Post
Sounds like the thermostat. If it's working properly the temperature should just rise steadily to the normal level & stay there. It shouldn't overshoot, as thermostat opening is proportional to temperature - there isn't a sudden change from closed to open.

Sorry mate but I disagree. I`ve fitted a few and new or old the cars often show a marked drop in temperature on the gauge when they first open. Especially when the ambient temp is low.
However a drop to 60 is a bit extreme so sticking is likely in this case, I just wanted to make the point that *some* drop is common on all thermostats, new or old.
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Re: Erractic Engine Temp

It's the tubes the fins cool, that become obstructed, especially if the coolant is not replaced at the recommended service intervals?:
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Re: Erractic Engine Temp

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Originally Posted by Chris View Post
Sorry mate but I disagree. I`ve fitted a few and new or old the cars often show a marked drop in temperature on the gauge when they first open.
That probably depends on where the temp sensor for the gauge is situated. The thing that gives cause for concern here is the overshoot - a few degrees, maybe, but not close to the top of the gauge, as described in the original post.
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Re: Erractic Engine Temp

Mine will slowly rise to around the 90 mark from cold, then when the thermostat opens drop down to below the 50-90 midpoint, then move up before it settles.

The Alfa temp gauge shows the ACTUAL temp, rather than the average that most cars show, so it tends to fluctuate more.
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Re: Erractic Engine Temp

New rad & thermostat should do the trick. The rad could be partialy blocked, but most likely thermostat sticking. As theres corrosion & the fins are falling off, a new rad is the must.
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Re: Erractic Engine Temp

Quote:
Originally Posted by Chris View Post
Sorry mate but I disagree. I`ve fitted a few and new or old the cars often show a marked drop in temperature on the gauge when they first open. Especially when the ambient temp is low.
However a drop to 60 is a bit extreme so sticking is likely in this case, I just wanted to make the point that *some* drop is common on all thermostats, new or old.
And I disagree with you! We keep getting this problem on these pages but mine was fixed (still is fixed) with the new thermostat. Under the old one it did steadily move up to running temp then suddenly fall.
The new one just steadily climbs to a crack under 90 and stays rock solid.
I suggest any sudden drop means the thing is sticking.
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Re: Erractic Engine Temp

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Originally Posted by Chris Nason View Post
The new one just steadily climbs to a crack under 90 and stays rock solid.
Perfect.
Exactly how it should be.
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