Temperature Issue

I'm gonna copy my origional post on another forum and then add what I've since done to try to correct the problem. Maybe someone else can help me.



[i]When I first got my truck, the temp gauge worked fine, from a cold start up would go to about 210, then the t-stat would open and the temp dropped to about 170 or so and sat there from then on.

After getting it back from having leaking intake gasket replaced, the temp would go up to 260 before it went back to 170 and then would sit for a little bit, go back to 210, back to 170, back to 245 or so, then back to 170, but It never seemed to run hot.

I changed the thermostat with a brand new 190* from NAPA and it seemed to cure a little of it. It still went to 260 before it opened and went to 170 or the normal operating temp.

NOW it warms up to 260, back to 170, back to 260, back to 170 just back and forth the whole time. If its on its way up to 260, and I slow down or stop, the temp stops as well, then when back in the throttle it drops then goes back to 260. I let it sit outside Saturday for an hour running and the gauge did the same thing, but It never overheated that I could tell. I was going to let it sit and run hot if it would b/c warranty would fix anything.

Is it the sensor, or t-stat, or water pump, or what???


I've since then replaced the t-stat again and the temp sensor in the driver side head. Now it does even worse than before, or at least registers worse. Ive also bled the system 3 times and no help there either.

Tell me the correct procedure to bleed the cooling system please and any other info you might know?


OH. When hooked up to a computer on the OBDII port, the temp reading there is alot different than the gauge reads.

Sounds like maybe a ground issue on the instrument cluster. Do you have a good ground from the battery to the cab? Is the ground for the instrument cluster in good shape? It could just be a bad gauge.

I haven't checked the ground for the cluster, as I haven't pulled it out yet. I was going to wait until I changed over to LED's. As far as the grounds outside the cab, they are all fine?

Is there one that goes to a head somehere I should look for that he might have un-hooked while replacing the gaskets?

On the head on the driver's side, backside of the head.

I'll look that over in just a little while during my lunch break and post what I found.

Went and looked. Didn't find anything. I couldn't get under it though. Should it be hard to locate or see?

The ground wires are between the firewall and cylinder head. That's quite a tight spot on the NBS trucks. My ground wires broke off of the terminal before. It's possible to happen to your's but not very likely.

I have an OBS that looks like yours, just a little newer and 4x4.

I'll just have to take a better look.

Now, to check the cluster ground...HA. Where to I begin?

I checked the back of the passenger head and found 2 grounds that were un-hooked. The shop schematic we were looking at showed 3 that are supposed to ground there but all I could find was 2...a ground stsrap and a ground out of a harness. Hooked them all back up and it still does the same thing.

Do you have a one wire or a two wire sensor? When you read the water temps through the OBD2 port, do the readings seem more logical? I'm thinking it may be the ground circuit for the guage in the instrument panel or corrosion in a connector between the PCM and the instrument panel adding more resistance to the circuitry.

One wire sensor. Just replaced it 2 weeks ago.

When reading it through the OBDII port it seemed logical the couple times we checked it. I might check it one more time today just to make sure.

One thing I did notice yesterday after we re-grounded everything and started it up was that when the gauge was climbing up to 260, the air the fan was pulling through the radiator was not all that warm feeling, then all of a sudden when the t-stat opened (after being on 260 for several seconds to a minute) it got HOOOOOOT! We used a laser thermometer to check the temp at the sending unit and it read 205 after the gauge had settled just below 210.

That sounds like it's got an air pocket in the engine. I'm not sure how you bleed air out of the older vortecs but you have to open the highest point on the engine and fill until water comes out of it.

I've filled it each time when I changed the t-stat, and have opened the radiator cap and let it run for God knows how long and kept it full. I can't find instructions anywhere.

<div class='quotetop'>QUOTE(JayBo &#064; Apr 25 2007, 10&#58;47 AM) [snapback]91351[/snapback]</div>

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I&#39;ve filled it each time when I changed the t-stat, and have opened the radiator cap and let it run for God knows how long and kept it full. I can&#39;t find instructions anywhere.
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Yeah, either air pockets or not the correct mixture of coolant/water. Bleed the system WELL. Most of the air in the system should burp out through the overflow tube...

Also make sure that the coolant/water mixture is either 60% coolant/40% water or 70% coolant/30% water. I use 60/40, but you may need a 70/30. It sounds like it is heating up fast, then the t-stat opens...it cools....t-stat closes....heats up....etc. You might want to try and install a lower temp t-stat. Your heater won&#39;t be as hot (and it will take a LOT longer for the motor to warm up), but we all know that heat is the main enemy of engine performance and longevity. A 180 t-stat may be what you are seeking...

I dropped it off at the shop yesterday while I went to pick up a new Hemi Charger I gotta equip, and this morning my mechanic calls me and says he started it up and sat there with an infared thermometer and shot it at the temp sensor while it warmed up.

He sais the head is ACTUALLY getting to 260 so its not a mis-reading. He said it stayed up at about 260-275 for a minute or so then the t-stat opened and it went to 205 or so then back up to hot and back to normal.

Could the guy that fixed it in the first place have installed the intake or head gaskets improperly and blocked off a coolant port?

<div class='quotetop'>QUOTE(JayBo &#064; Apr 26 2007, 07&#58;55 AM) [snapback]91443[/snapback]</div>

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I dropped it off at the shop yesterday while I went to pick up a new Hemi Charger I gotta equip, and this morning my mechanic calls me and says he started it up and sat there with an infared thermometer and shot it at the temp sensor while it warmed up.

He sais the head is ACTUALLY getting to 260 so its not a mis-reading. He said it stayed up at about 260-275 for a minute or so then the t-stat opened and it went to 205 or so then back up to hot and back to normal.

Could the guy that fixed it in the first place have installed the intake or head gaskets improperly and blocked off a coolant port?
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Yes, that is a very possible scenario. Blocking off one port should not let the block or head temp rise to that point though... I am not sure, but 260-275 is pretty damn hot for the 5.7L Vortec to be running. I would say that 240 is the max temp. where it should run... Try installing a 180* t-stat. I know that installing a lower temp t-stat will not solve the problem with it fluctuating so frequently, but it will help keep the temps in a more normal range. You may want to do a REALLY GOOD coolant flush, then mix in the coolant a little thicker than the water (65-35 mix) and do the 180* t-stat...

Its up to the mechanic now. I gave up on it and put it in the shop. He said they&#39;d more than likely want to take the intake back off and replace BOTh head gaskets this time instead of just one like the other jack leg did.

I&#39;m going to take pics and document the whole thing if thats what they do so the warranty company won&#39;t try to sue me&#33;

if they decide not to, I&#39;ll do the steps you listed above. Thanks&#33;

After doing some testing yesterday, we found out that ONLY the head that jackass worked on is getting up to 240+ degrees. The one he left alone didn&#39;t get above 195. So its gotta be something either in the intake gasket or the head gasket. It&#39;ll be torn apart next week and fixed.

<div class='quotetop'>QUOTE(JayBo &#064; Apr 27 2007, 08&#58;35 AM) [snapback]91546[/snapback]</div>

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After doing some testing yesterday, we found out that ONLY the head that jackass worked on is getting up to 240+ degrees. The one he left alone didn&#39;t get above 195. So its gotta be something either in the intake gasket or the head gasket. It&#39;ll be torn apart next week and fixed.
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Good to hear that your mechanic finally figured out what went wrong. Hope all goes well after it is fixed.

Thanks man. I&#39;ll post what was wrong so everyone can laugh&#33;