99 yukon intermintent overheating and cold air

[tentitans70]

I just purchased truck, noticed water temp guage went up to a hair below red mark within 5min down the road. Pulled over and put in park and temp came down(to about half of guage). Then drove 15 miles and temp went up and down (up to top of guage and down to about 180 ?? I'm guessing) The couple times it went down to the lowest temp is when I actually got a bit of hot air from the heater. Except for that I only had cool air from the heater.


I am thinking thermostat unless I find that it is low coolant or air in the system.

Can anyone confirm that or had the exact same thing happen. I would just like to fix on thing if possible and not just R&R until it's fixed.

Thank you.

Also did not see a search function on this forum to find previous topics on this issue.

Please give me some good news.

 

[718frankb]

change the t stat and run motor w/cap off the rad for a few minutes also when you reinstall the bolts on the t stat clean off the ground wire its a ground for the temp gauge . welcome to the forum!

 

[tentitans70]

change the t stat and run motor w/cap off the rad for a few minutes also when you reinstall the bolts on the t stat clean off the ground wire its a ground for the temp gauge . welcome to the forum!

Thanks for your response.

One other question if I can, truck had check engine light when I was checking it out. Hesitated buying until they could clear it up. I was there when they put a scanner on it and it showed #3 cylinder misfire, also the icons for oxygen sensor and egr valve where flashing on the scanner.

Now they checked it out and cleaned up a spark plug and got the check engine light to go out. Still a tad rough at idle but not when accellerating. Figure oxygen sensor is issue. Just after driving about 25 miles in 2 trips I was showing rig to my wife and is was just running at idle and got a bit rougher and engine light on again.

Sound like oxygen sensor? or position sensor? or EGR valve?

Also comming home after work on that leg of the drive today I got plenty of heat and water temp never went above 3/4 of the guage.

Thank for any that can help.

 

[Dan1987]

after you put the new thermostat in open the radiator cap and run the motor untill its at operating temp. Look down inside the radiator and see if there are any bubbles comming up. I know this sounds crazy but i struggled with this over a year on my 88 chevy. Cooling problems replaced everything new radiator and anything that had to do with the cooling of the motor. I talked to a local radiator shop in town and he told me it might be a head gasket he said he has never seen it but has heard of it before i didnt believe him. Turns out it was a blown head gasket that was leaking from a head bolt that went through the water jacket on the heads to one of the cylinders. When the stress and temp was just right it would open a pen hole and blow hot compression into the water jacket untill the coolant would boil. over the year it got worse untill it was blowing coolant out of the over flow. One day it wouldnt start sounded like the motor locked up and i knew one of the cylinders was full of coolant. i never let it over heat so all i had to do was put a new head gasket on its ran for over a year then i sold it no problems. I had problems with my heat to but as soon as the air got out of the system it would drop 80 deg. and be just fine. Just a thought

 

[718frankb]

do a small tune up new plugs and change oil .while you change the plugs disconnect the neg on the battery that will clear the trouble codes when your done reconnect and drive about 25-30 miles if it sets a new code then have it checked on a scanner.just because it sets a o2 code doesnt mean it the sensors are bad its most likely the cats are bad. also look at the condition of the plugs from each cyl that will give you a good idea of whats goin on- corroded,oily etc... good luck

 

[tentitans70]

do a small tune up new plugs and change oil .while you change the plugs disconnect the neg on the battery that will clear the trouble codes when your done reconnect and drive about 25-30 miles if it sets a new code then have it checked on a scanner.just because it sets a o2 code doesnt mean it the sensors are bad its most likely the cats are bad. also look at the condition of the plugs from each cyl that will give you a good idea of whats goin on- corroded,oily etc... good luck

Yeah, I do need to do some of the simple service and tune up items that will help narrow down the problem spot. It seems to run strong otherwise, so I have at least some hope that I got a decent rig. I will probably clean out the mass air flow sensor and egr valve.

What's best for cleaning those out?

 

[tentitans70]

Ok,

I might have found what is all going on in a nutshell.

This morning was my first chance to check over things that might be problems and this is what I found and my thoughts on it:

For the water temp issue - There was no coolant in the overflow tank and the radiator was down about a quarter. So put in 3/4 of a gallon between the two and will keep an eye on things ( leaks, fluid level and yes I am aware of the intake issue but see no signs of it so far.) Mine had the green coolant in it and was fine with me even though I have heard the argument of using only the dexcool stuff. No thanks I say. Good thing is I found no coolant in the oil or the other way around. Will be needing a rad flush though.


For the rough idle issue - bear with me. - Found the air filter completely saturated with dust. Sort of like what one of those canister filters on a vaccume cleaner looks like when it needs cleaned. I am thinking with next to no airflow there was not the right air/fuel mixture and that was causing a misfire (#3, possible others) and with it running rich over time it was probably gunking up the EGR valve and affecting the O2 sensors. All of which showed up on a handheld scanner when the dealer checked codes when I was there ( I saw the scanner screen myself ) and would also futher make the idle rought individually let alone togther. At least that all makes sense to me. The INSIDE of the air filter and ducting leading to the mass air flow sensor was clean and looked fine.

I was very happy to find those two definetive issues when checking things out and how it may point to simple fixes. I am keeping my fingers crossed.

Other than that the rig drives and runs fine and is clean and in quite good condition.

What do you guys think? Does that all make sense???