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Discussion Starter #1
Guys I have some problems that have stumped me and need input. Last summer noticed on some really hot days temp gauge would hit 3/4 and above but never would get to the point where I needed to shut it down. Now that it's cool gauge never gets past 1/4 if it makes it there at all. Also in summer if I shut the engine down it will not start again till gauge drops below 1/2 (acts like it's flooded). It will also on some days if it idles for a while like sitting in traffic or school line it will start to spudder and sometime shut off it will start back but it runs like crap till I can start moving again. I have changed temp sensor,both o2 sensors,fuel filter,cleaned mass air sensor & throttle body. Last week I changed out the old mass air sensor to a new one drove it to work (about 50 miles round trip ) truck spuddered the whole way even at highway speed at a stop had to put it in neutral and give it gas to keep it running. Took it off and put the old one back on and it went back to just being randomly crappy. So I changed or checked everything I can think of in no way am I an mechanic. Hopefully one of you guys can point me in the right direction. Sorry for the long post wanted to make sure got all the symptoms in there. Thanks guys
 

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Id replace the thermostat. Never replaced one on a Colorado but most of the are under $15 and dont take long to change.

Edit: Do you have any way of looking at the engine temp other than the factory gauge? If not you might want to look into an ultragauge/scangauge or something like that. Lots of info already on here about them. But yoy could also look at fuel trims ans such when its stumbling to see if its getting gas.

also mighy check spark plugs and coils.
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Id replace the thermostat. Never replaced one on a Colorado but most of the are under $15 and dont take long to change.

Edit: Do you have any way of looking at the engine temp other than the factory gauge? If not you might want to look into an ultragauge/scangauge or something like that. Lots of info already on here about them. But yoy could also look at fuel trims ans such when its stumbling to see if its getting gas.

also mighy check spark plugs and coils.
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I'd start with the thermostat too, AutoZone about $40.00 (we have a hose fitting on it so more than most.
A failing coil could also cause some extra struggles for the other 3 cyls I would think.
Another less popular problem might even be a bad head gasket. You getting any other symtoms like oil in water, water in the oil, etc?
 

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Discussion Starter #4
Not that I have noticed what would beore symptoms for the head gasket?Also first thing I thought of was the thermostat but wouldn't that cause either a always hot or always cold (stuck open or closed)? Not trying to argue just trying to rap my head around it with limited knowledge.
 

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Not that I have noticed what would beore symptoms for the head gasket?Also first thing I thought of was the thermostat but wouldn't that cause either a always hot or always cold (stuck open or closed)? Not trying to argue just trying to rap my head around it with limited knowledge.

I had a 'sticky' thermostat in an old S-10. Some days ran hot, some days never warmed up until I was at work. In the Colorado, I changed it at 100K miles because I figured it had to be close.
As far as bad head gasket, bubbles in the radiator, oil too. Water in the oil. All depends on where the gasket is bad. Low compression in a couple of close cylinders.

I'm only a shade tree mechanic, been that way for tooo many years to change now. Someone with a real knowledge of heads and head gasket problems could help more I'm sure.
 

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Having a failed coil won't make the other cylinders work harder. They all one one job...fire. If one coil doesn't work the others don't get overtime.

OP, do you have any codes? It seems to be common for the t-stat to fail in the open position. I'm sure that is by design (prevents overheating). Then when it's open it throws a code suggesting the coolant isn't normal.

If you change the t-stat, you're going to find it runs warmer because the new t-stat (by GM design) is hotter than the one in your truck from the factory.

I'd suggest first reading the coolant temperature before you get too involved with anything else. You can get an infrared tool yourself, or take it to a shop and they can shoot the radiator and measure the temp. Then that is ruled out and you can look elsewhere.

How has your mileage been? Any idea? In most cases when the truck doesn't warm up it runs rich.
 

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I think some kind of scanner that will give you temps and fuel trims is a good investment . You could check engine temps, oil pressure, fuel trims, ect. Could pay for its self pretty fast by not guessing and checkr so much, not replacing good parts

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Discussion Starter #9
I'm hoping not the head gasket I never have to add water/coolant. radiator and reservoir stay full I don't add but about a quart of oil between changes but do have a small leak coming from the top passenger side of the engine looks to be the valve cover. However if it is the hg how much damage have I done by driving it.
 

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I know you said your not losing any coolant but jave you checked the condition of it? Id siphon some out and see if there's any oil in it.

Also a compression test could tell a lot. I think most parts house's will let you borrow/rent the tester. Its easy to do and can tell you a lot about the health of your engine.

When you change your oil has it ever looked milky?

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Replace the thermostat. My truck did the same thing. It run real cool then hot on warmer days. Then it go to the point when it reach operating temp it kill the truck do to lean conditions vuase the ecu can tell what the actual temp is for correct air/fuel mixture. Once installed clear any codes and it has ran beautiful since.
 
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