So ive had my car for 2 years, got it at 60k and put on 36k, sitting at 96k atm. About a week ago i noticed my temp gauge was in the red, the wtf u dummy light came on, and i immediately killed the engine to prevent any damage. My car is my baby and i do everything by the book and go above and beyond in reference to preventative maintenance. I turned the car on about 5 minutes later and it was fine, engine temp was normal, just below half. Now because the radiator had been flushed and replaced with new coolant, I believe that air is being introduced into the system. As i drove into town the gauge would go up, then go back down, fluctuating constantly. When I got home i did a bleed of the radiator with the cap off and the engine running. I added coolant to top it off after about 5 minutes and just before it started to overflow from the temp going up. I went back to the gauge and it was in the right spot. Its been a couple of days and the coolant is going down and the gauge is starting to bounce around again, but not to the extremes it was previously.

I then examined the side of the lower intake manifold in the sunlight. Theres wetness because of what i believe is a broken gasket (gm thought it was a GOOD idea to put in plastic gaskets instead of metal/rubber.) The wetness is a streak on the passenger side and a couple spots on the driver side. Also wanted to add i did the T stat myself at 76k miles and got the most expensive one(in hopes it would last the longest) I believe their is air being introduced into this closed system and thus is why the gauge bounces around. I am for sure losing coolant because ive topped it off twice now,not much, but i shouldnt be losing ANY. What are some ways i can tell if my head is leaking besides sniffing the back exhaust?? Any special tests I can do? Any thoughts on this matter would be greatly appreciated!!!

Duncan~~

 

Is there coolant in your oil? Is there a milky white color forming on your oil cap? These are signs of a head gasket issue.

The 3400 is known for head gaskets and LIM gaskets leaking coolant and needing replaced. You may need to replace both gaskets.

 

About to change the oil tomorrow, ill update if there is any coolant in the oil. Im debating on doing a complete teardown to the heads at 90k, or waiting until the problem starts (I had a bad head gasket experience on the other monte.)

 

A compression test will also tell you if your head gasket is failing, but as MAMONTE said, it could be your LIM gasket.

 

When my headgasket went, I was constantly having air in my cooling system. No matter how much I bled the car, it would get air in it, in a mile.

 

Ive never done a compression test, but I do have the gauge for it...Now if I run a compression test on each cylinder, will that damage my engine? Does having a non working cyclinder damage the engine? Granted i wouldnt run it like that for long, but ive never performed the check before so any tips on it would be very helpful. Thanks!

 

if you air burning coolant in the engine an abnormal amount of steam will be present at the tailpipe or its leaking into the crank at which you will have the missing water in your oil pan. LIM (lower intake manifold) gasket do blow/leak quite often, I have done the LIM gasket on my chevy 1500 twice in 6 years now and can be a pain but do-able (my first i was 16). Try letting the var dry off for a few hours so you dont have any access fluid from topping it off, either on the block or on the ground. If its a LIM leak it will run off the engine. unlike head gaskets that normally spill into engine. Once you have allotted adiquite time for her to dry off. seal the cooling system and rev the engine a few times (around 2,000 rpms is fine) and inspect the engine for spurts/streams of cooling running from underneath the LIM.

Locating the LIM is simple, from the front of the engine locate the valve covers and find where they meet the heads. at that corner the manifold meets the head and the LIM. Follow its perimeter checking for leaks.

although, judging by your description of the speed at which the temperature fluctuates and that it spikes during city driving more? the Thermostat maybe stuck open, not giving the radiator enough time to do its job.

I would First:
1) check exhaust for a sweet smell or excessive steam
2)check the LIM for leaks
3) change the oil (if you haven't already done so) it will be a mustard color if there's leaking. it will also drain an excess amount of oil.
4) Drain the coolant and replace the thermostat if none of those are true.

Hope this helps!

 

Also check your heater core fittings, as this is what happened to me. Im not 100% on the 3400 but it should be around the same place. Check your belt tensioner. Heres a vid

http://www.youtube.com/watch?v=IFiICANvre4

 

Changed the oil, im now at 98.6k miles. No milky or abnormal colors in the valve cover area. Ive gone through about a gallon of coolant (ive been topping it off as the levels drop) since i last posted (about 2500 miles). I stuck my finger in the exhaust and smelled it, it was coolant. I am burning it for sure. I bought a tester for the cylinders that I will conduct tomorrow (for the heads) I will test the amount of pressure they can hold over X amount of time. That way I can determine if I need to change the heads as well as the LIM. Wish me luck!

 

no need to buy new heads unless they are cracked, and if the aluminum head cracks it will actually break off, send them off to a machine shop to get them flatten down, i just did mine all myself, final cost was around $700. and make sure you flush out that bull**** dexcool and switch over to green coolant.