Help diagnose a truck anyone?

[jimbob200521]

So this past weekend, I did some servicing on my truck (I'll explain what I did in a sec). It's a 2001 Silverado with the 5.3 Vortec engine in it and just around 128k miles. Today, I took it to run a few errands for work and of course, it's a good hot day here (mid 90's with heat index). Ran to Menards, all was ok. Ran to Kroger and let the truck run while I ran in to grab some bread and crackers, I was in 10-15 minutes (of course, I ran into a friend). Came back out and my temp gauge was nearly pegged in the red. I drove back to work hoping getting some air moving over it would calm it down but it didn't. So I parked it and when I get off work, I'll have to investigate more.

Now, the servicing I did. Saturday I pulled the intake manifold to replace both knock sensors, wiring harness, and intake manifold gaskets. I replaced the gaskets with new Felpro gaskets. Reinstalled everything and took it for a good run in the country to make sure my knock sensor problem was cured. It was, and all other gauges (including temp) were normal when I got home. Monday, I dropped the trans pan, changed about 5qts of trans fluid, the pan gasket, and the trans filter. Again, took it for a ride and all was good.

Then today, for the first time since I've had the ol' girl including some much hotter days than today, my temp gauge is nearly pegged and my dash tells me to check coolant temp.

My thoughts are either timing sucked and my thermostat went out making me think that some of the other work I did affected the cooling system some how OR something I did on the top end of the engine messed with the cooling system (vac line? coolant line?) but seeing as how things went back together the same way they came off, I don't know what it could be.

Anyone have any thoughts on this? I'd love to have some things to look for before I dive back into taring the top end off to double check my work blind.

[olds45512]

I would start with a thermostat and go from there. I always test new thermostat's with a temp gun before I install them, I had three bad one in a row once and learned that lesson the hard way.

[Alvy]

Ryan a couple things come to mind. Did you take off the serpentine belt to do these repairs and possibly put the belt back on wrong? Also, does it still have the OE mechanical fan w fan clutch? There's a lot of aftermarket companies that have electric fan conversions and if yours was converted maybe a wire or connection was knocked loose. Hopefully it's as simple as that or a t stat and not a head gasket. Lots of guys I know have the vortec 5.3 and rawdogged it way past 128k miles with no over heat issues so I would think not. Crossing fingers for you.

[IHinIN]

You could have an air pocket in the cooling system. When I changed intake gaskets on my '94 Chevy 350, that happened and the temp gauge almost pegged before the thermostat opened and the temp dropped to normal.

[jimbob200521]

Originally Posted by olds45512

I would start with a thermostat and go from there. I always test new thermostat's with a temp gun before I install them, I had three bad one in a row once and learned that lesson the hard way.

How would you test a thermostat out of the vehicle with a temp guj before installing?

On a more info note: when I got home I popped the hood and out a fan on the engine whole I double checked a few things. I took an 8mm and 10mm socket and along with a visual inspection, made sure things were snugged up and I didn't miss anything when I worked on it Saturday. Nada. Next, I took it for a drive, paying careful attention to the temp gauge. I drove and got to operating temp and it held there for a quick minute, then started shooting up towards the red line again. It shot to about 235° when I pulled in the driveway and shut it off. When I say shot, I mean it moved very quickly. Starting to thing thermostat. Either way, I hate doing proper maintenance on something then something else crops up. Ugh frustrating sometimes

[jimbob200521]

Originally Posted by Alvy

Ryan a couple things come to mind. Did you take off the serpentine belt to do these repairs and possibly put the belt back on wrong? Also, does it still have the OE mechanical fan w fan clutch? There's a lot of aftermarket companies that have electric fan conversions and if yours was converted maybe a wire or connection was knocked loose. Hopefully it's as simple as that or a t stat and not a head gasket. Lots of guys I know have the vortec 5.3 and rawdogged it way past 128k miles with no over heat issues so I would think not. Crossing fingers for you.

No sir the serpentine belt did not come off at any point. This engine also has a dry intake so even if the intake was left off, it wouldn't affect the cooling system (you know what I mean ). And finally, stock fan system and I can confirm the fan seems to be working with no issue. I'd stick my fingers in there to test my eyes but I like having my fingers

Originally Posted by IHinIN

You could have an air pocket in the cooling system. When I changed intake gaskets on my '94 Chevy 350, that happened and the temp gauge almost pegged before the thermostat opened and the temp dropped to normal.

I believe this truck has a dry intake so nothing I really did SHOULD have affected the cooling system.

[jimbob200521]

One thing I forgot to mention about my later test drive: when I was getting close to home, I cranked the heat full blast and it came out...warm. Not hot at all. Starting to seriously think thermostat.

[olds45512]

Originally Posted by jimbob200521

How would you test a thermostat out of the vehicle with a temp guj before installing?

I meant heat gun.

[Alvy]

Or put it on the stove in a pot of water with a thermometer and monitor temp when it opens

[olds45512]

Also check the lower rad hose, when they get soft the water pump can suck them shut and cut off the flow.