Ideal engine temperature - Alfa Romeo Forum
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(Post Link) post #1 of 24 Old 15-12-10 Thread Starter
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Ideal engine temperature

Just had a new engine fitted in my GT after a bottom end failure (overheated crankshaft, bearing shelves melted). It's a 2.0JTS. Old engine had only done 51k miles. I've noticed that the new engine doesn't seem to get as hot as the old one. Whereas the old one was almost always reading 90 on the temp. gauge, the new one's steady at about 70. I'm wondering if the old one was running too hot all the time and this contributed to the failure over time, or if the new one is running too cold and it should be at about 90 ? Is it because it's a new engine ? (Can't remember what the old one was like when I first brought it). Appreciate any comments/advice anyone can give me.
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Should be at 90 all the time once the engine has warmed up.
No matter what speed you are doing or how cold it is outside.
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Also the gauge often tells lies.

You really need to hook the car up to Alfadiag or othere diagnostic program to get the temperature reading that the ECU sees.

The gauge on my GTV V6 was consistently reading 10C lower than the real coolant temperature, and it was only when I fitted a new thermostat that I realised the old one was actually ok...
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i replaced my stat early last year after the gauge rarely got much above 50, since then it warms to just over 90 when the fan kicks in then sits at 80ish unless in traffic
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Sounds like you got a random old thermostat from the old cylinder head fitted to your new engine, rather than a new one (or your old, working one).
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Quote:
Originally Posted by symon View Post
Also the gauge often tells lies.

You really need to hook the car up to Alfadiag or othere diagnostic program to get the temperature reading that the ECU sees.
Absolutely....
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Quote:
Originally Posted by jaypeebee View Post
i replaced my stat early last year after the gauge rarely got much above 50, since then it warms to just over 90 when the fan kicks in then sits at 80ish unless in traffic
Mine always sits between 50 and 55.

I thought this was a little low so i decided to let her run idle for 10 minutes.

The temp rose to about 90 and just after that the fan kicked in to take her back down to 85 - 90 ish.

Does this mean I need a new thermostat? Surely if the thermo wasnt working then the heat would have just continued to rise? Any suggestions?
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Quote:
Originally Posted by Chenzo View Post
Mine always sits between 50 and 55.

I thought this was a little low so i decided to let her run idle for 10 minutes.

The temp rose to about 90 and just after that the fan kicked in to take her back down to 85 - 90 ish.

Does this mean I need a new thermostat?
Yes

Quote:
Originally Posted by Chenzo View Post
Surely if the thermo wasnt working then the heat would have just continued to rise?
No it wouldn't. Because the thermostat is stuck open. So coolant is always flowing through the rad, even when the engine is cold.
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Okey dokey - yet another thing to fix - oh joy! still, she may be a bit nippier afterwards!

Thanks for the advice - thank God Alfa had the good sense to have the default as open!
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Quote:
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... thank God Alfa had the good sense to have the default as open!
Not just an Alfa thing.
Most thermostats stick open when they fail.
Very VERY unusual for one to stick closed.
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This is going back some but I had a Renault 5 which stuck on closed u can guess what happened next!

Now I just need to figure out which one of the two types of thermostat I need. Hope the part is visible in the engine bay so I can compare!
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My 1.6 twin spark used to run at 70 and go up to 90 in traffic, after the thermostat change the needle now splits the 9 on the gauge. Probably about 85.
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I was always told 82 degrees was the sign of a good cooling system 90 is when most fans kick in
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Interesting thread. Hope this isnt too much of a hijack, but i am a month into my first diesel engine ( mgzt cdti ) and it seems to run cool. There is much discussion on the pipe&slippers forum regarding the low temps people get in the winter ( mine is never 1/4 with 1/2 being normal. Heater takes 10 miles to warm up).

This is mostly due to the regular failure of the thermostat but its a pig to change on the zt. So people want to fit in-line stats in the top rad hose. Thing is, i am not convinced they know what temp they are aiming for while stat testing. General concensus says it should be 80 -90 but i am yet to see any evindence.

I want to know what the ideal operating temp for a diesel engine should be. Anyone know ?
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the ideal engine temperature is a mainly related to the oil ... too cold and the oil is too thick, too hot and the oil doesn't protect the engine well enough ... 80-90 seems to be about the standard though
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Makes me wonder why in the uk we need oil coolers
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Makes me wonder why in the uk we need oil coolers
I ran a 3 litre engine in my old 156 with only a oil:water heat exchanger, rather than using an oil cooler.
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My 164 24 valver had a leaking oil cooler and for a quick fix i got a peice of hydraulic oil pipe with a union at each end and fitted it to the car where the oil cooler once was
ran it for years without a single problem
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Quote:
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Makes me wonder why in the uk we need oil coolers
For when we drive our cars to Italy???
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It should sit at 90, take action when it fails to go above 80
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Quote:
Originally Posted by symon View Post
Also the gauge often tells lies.

You really need to hook the car up to Alfadiag or othere diagnostic program to get the temperature reading that the ECU sees.

The gauge on my GTV V6 was consistently reading 10C lower than the real coolant temperature, and it was only when I fitted a new thermostat that I realised the old one was actually ok...
I will go with symon on this having used diagnostics, guage showing a lot lower than indicated by diagnostics. The number of times this subject crops up, before you throw money at anything get it checked. Whilst replacing the stat has worked for some, others on this site have had no change to the temp reading. A good investment is a second hand laptop, cables and free fiatecuscan software.
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90 degrees =)
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(Post Link) post #23 of 24 Old 17-02-11 Thread Starter
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Thanks for all the comments. Finally found the time to get it back to the garage that did the engine re-build. Told them it's not reaching the correct temperature on the gauge and feels a bit 'lumpy' at tick-over. Took two hours out of my day at work (nice but obviously not ideal) to be told that the engine is running as they would expect and since no fault-codes are showing they can't do anything about it. Said if it's the thermostat they'd need the car from cold. But reading the posts here, can't the diagnostics pick up if the engine is at the correct temperature ? I am admittedly a numpty where most of the finer points of car maintenance are concerned, so should I get it into a reliable independant for them to check it for me ? Oh, and they also had the cheek to sting me 17 quid for a new sidelight bulb !!
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sidelight bulbs aren't cheap... 4 a piece is about what I'd expect... then there's fitting which can take a couple of minutes... depending on the rates they charge it wouldn't be a total rip off...

you could've bought your own sidelight bulb and fitted it yourself
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