low and irregular operating temp

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geezer - 10 Dec 2005 11:17 GMT

now that our daily temps are in the teens my 2004 gmc 1500 sierra with the
small v8 won't maintain normal operation temp of 200 degrees. It will reach
200 going up hills or running on the interstate but immediately starts to
cool down when coasting downhill or driving around town. I got the dealer
to install a second new thermostat yesterday but if anything that just made
it harder to warm up, I drove around town for 1 1/2 hours last evening at
about 170 degrees. Now I know that ain't right and i think it effects my
gas mileage too. So what should I do?

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putt@webtv.net - 10 Dec 2005 13:55 GMT

>my 2004 gmc 1500 sierra with the small
> v8 won't maintain normal operation
> temp of 200 degrees.

If you are relying on the factory gauge for correct temp: those are
unreliable. It may be out of calibration. Since you paid someone to
replace the t-stat, do you know if the correct 'range' unit was
installed? For good heater operation, at least a 180° stat is needed.
If you are in a really cold area, a 190° stat is better. I'd start
with making sure the gauge is accurate....NOT(normal operating temp) in
a well-maintained cooling system is 210°-220°. Hope this is of some
use.....

Dave S(Texas)

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geezer - 10 Dec 2005 21:03 GMT

thanks putt-yah the gauge works and was backed up by the dealers computer,
and I'm on the third tstat already. All spring summer and fall it runs
about 205 but when the outside temp falls below about 20 the truck won't
maintain a steady temperature while I'm driving around. is still under
warranty but pissing me off

>my 2004 gmc 1500 sierra with the small
> v8 won't maintain normal operation
> temp of 200 degrees.

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Woody - 11 Dec 2005 00:07 GMT

It probably is just running efficiently and not wasting a lot of gas making
heat. Some gauges will fluctuate depending on where they are in the block.
What temperature does the OBDII tester show? That is what is controlling the
engine. What temp thermostat is in the engine? It is possible your fan is
running all the time causing excessive cooling.

> thanks putt-yah the gauge works and was backed up by the dealers computer,
> and I'm on the third tstat already. All spring summer and fall it runs
[quoted text clipped - 16 lines]
>
> Dave S(Texas)

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geezer - 11 Dec 2005 11:50 GMT

the mechanic's tool plugged into my truck (I guess that's his OBD II),
mirrored the gauge in the dash. you can see the temperature drop while the
truck idles (right after I finally got it up to 200 on a long hill). They
told me the correct thermostats were installed. I'm especially concerned
because my gas mileage drops from about 17.5 mpg to 13 mpg when this cooling
problem is going on. It could be related. I'll check to see if the fan
isn't shutting off. The service manager is checking to see if somehow the
wrong radiator got installed during production. Thanks for your help.

> It probably is just running efficiently and not wasting a lot of gas
> making heat. Some gauges will fluctuate depending on where they are in the
[quoted text clipped - 22 lines]
>>
>> Dave S(Texas)

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=AB Paul =BB - 11 Dec 2005 15:16 GMT

> the mechanic's tool plugged into my truck (I guess that's his OBD II),
> mirrored the gauge in the dash. you can see the temperature drop while the
[quoted text clipped - 4 lines]
> isn't shutting off. The service manager is checking to see if somehow the
> wrong radiator got installed during production. Thanks for your help.

Engine temp is supposed to be maintained by the thermostat
by regulating the amount of water flowing through the radiator.
Too large of a radiator should not matter unless too much water
were getting past the thermostat into the radiator via the bypass
hoses/pipes. I wonder if there should have been a restrictor in
the bypass that got left out at the factory?

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geezer - 11 Dec 2005 17:35 GMT

there is there a bypass around the thermostat? I wondered because I thought
like you about the radiator, but i couldn't imagine this problem going on
after 3 thermostats. to my way of thinking there has to be a bypass and it
has to be wide open, maybe it's in the radiator, i have no idea. But even
just now i drove 30 minutes and 15 miles and it barely got over 160 degrees
and it is 33 outside. I'll tell/ask the service guys about the bypass
tomorrow- thanks

"« Paul »" <"=?x-user-defined?Q?=AB?= Paul
=?x-user-defined?Q?=BB?="@houston.rr.com> wrote in message
news:439C42B3.A6C1BBDF@houston.rr.com...

>> the mechanic's tool plugged into my truck (I guess that's his OBD II),
>> mirrored the gauge in the dash. you can see the temperature drop while
[quoted text clipped - 15 lines]
> hoses/pipes. I wonder if there should have been a restrictor in
> the bypass that got left out at the factory?

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geezer - 11 Dec 2005 11:58 GMT

If an OBD II is the tool the mechanic plugged into my truck it showed the
same temp change as my gauge. After I finally got it up to 200 the tool
showed it cooling off while at idle too. My mileage drops from about 17.5
mpg to about 13.5 mpg at the temperatures (below 20) when this cooling thing
goes on. It might be related, I don't think it should drop that much just
because it's cold outside. I think the truck needs to run over 200 for the
computer to send the right fuel mixture. I'll check the fan to see if it is
not shutting off. They tell me the correct thermostats have been installed
and are looking in to seeing if somehow the wrong radiator got installed
during production. Thanks for your help.

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