Help with my '99 coolant problems.....

I have a '99 with approx. 139,000 on it..I have two issues which are stumping me....

#1) Mysterious coolant leak from the front of the engine, dripping by the oil pan area.....amount varies from a couple of drops to a few ounces, and seems more frequent when it is parked on an incline...No leak visible from heater hose to intake, and the waterpump is less than a year old so I doubt that is a weep hole seep......

#2) After sitting, it seems that it takes longer to get to operating temp (165f to 190f is the norm on my Tahoe). The needle then swings from 210f to "pegged", and then the "check guages" light comes on. After about 8 seconds, the needle dips back to norm temp (165F). if I have the heat on, it blows cold to mild until the needle "pegs" and only blows warm after it returns to normal....initially I assumed this to be a thermostat issue, but after replacing the thermostat twice the problem still remains........

I do not know if these problems are related or not, I have had the leak for a while now and the temp issue has surfaced a couple of days ago....

Any help or advise would be greatly appreciated!
thanks....


Any help or advise would be greatly appreciated.....

Check for worn or slipping belts. If the belt is slipping, it can cause the water pump not to spin as efficiently. Also check for debris build up on front of the radiator. Have a pressure check on the cooling system performed.
As for the leak, check the pump to block mating surfaces for signs. Other possible areas are intake and head gaskets, freeze plugs, possible cracked block or heads.

engine temp

if your engine is running at 180 degrees that is TOO hot!!!

mine stays just under 160 as it should. your needle on the gauge should be in the middle, preferably to the left of the middle.

i had a coolant leak and mine was running hot about 2 months ago. dealership tried to replace the radiator for big bucks, but i look under the hood and saw it was leaking from a plastic "thingy". autozone told me this "thingy" was my heater valve. i got a new one for $13 and installed it in 20 minutes. been running cool ever since. now i just need to buy some coolant before the water in there freezes!

lol

Alright, I am still stumped.....

I replaced the belt when I replaced the water pump, but I checked it anyway...it's still new and not slipping.

I also cleaned out the front of the radiator while everything was loose....I removed the leaves, bugs, and found the 3/8th's socket wrench I had been looking for.....

this is still happening:

After sitting, it seems that it takes longer to get to operating temp (165f to 190f is the norm on my Tahoe). The needle then swings from 210f to "overheated", and then the "check guages" light comes on. After about 8 seconds, the needle dips back to norm temp (165F). It then floats around slowly from 165F to 210F for the rest of the drive, sitting at 165F most of the time. If I turn the heater on at startup, it blows cold and only warms up after about twelve minutes or so. if I turn the heater off and wait until the needle stabilizes at 165F, when I turn the heat back on it blows hot like it should.......

As for the leak, there are no visible signs of leakage anywhere. I had this leak before I replaced the waterpump, so I do not think it is coming from the pump/block mating......

Any suggestions??...

Man, it sounds like you have an air pocket to me. When the engine is cold and off, take the radiator cap off and start the engine. Turn the heater on so the heater valve is open and coolant is flowing through the heater core. While the engine is running, add coolant till it tops off. Try that and see if that helps.

don't know if'n it's been covered yet, sorry if i'm repeating common knowlege; get the gm dexcool out of your system. have it flushed and replaced with the good ol cheap green stuff. don't like to type, if you want that elaborated upon, your local radiator shop can go much farther in depth.

JKmotorsports said:

Man, it sounds like you have an air pocket to me. When the engine is cold and off, take the radiator cap off and start the engine. Turn the heater on so the heater valve is open and coolant is flowing through the heater core. While the engine is running, add coolant till it tops off. Try that and see if that helps.

Click to expand...

great diagnosis JK, I can't thank you enough!!.....

I did this today, and sure enough I got A "burb" out of my radiator...after that I topped it off and now the temperature guage is functioning as it should.....

Now if I could just locate that slow coolant leak.. I was under my Tahoe today and it seems to be seeping somewhere above the starter....

that leak sounds like either rear of the intake manifold dripping down the back of the engine or the freeze out plug above starter.

421racing said:

great diagnosis JK, I can't thank you enough!!.....

I did this today, and sure enough I got A "burb" out of my radiator...after that I topped it off and now the temperature guage is functioning as it should.....

Now if I could just locate that slow coolant leak.. I was under my Tahoe today and it seems to be seeping somewhere above the starter....

Click to expand...

:thumbsup: Glad you got that part of the problem fixed.
Good luck on the leak. Might be easier if you can get enough light under there and try to trace the leak upwards to its source. If you let the engine warm up, the cooling system will build pressure and more than likely start forcing coolant from the source of the leak, making it easier to find.

There is no visible leakage coming from the intake mainifold or anywhere above the area circled in the photo... I cleaned the area with a rag and sat back and watched it......Coolant slowly seeps out from that corner after a few seconds.....I am afriad that it is indeed the Passenger side head gasket...

That being said, my Tahoe has 140K on it....If I have to replace the head gasket, should I just get a top end rebuild?

Or go all the way and get the motor rebuilt??

Or just get a new long block?......

if it originates from that corner only, then it is infact a head gasket problem. i would do just a head gasket job on it. are you doing it yourself ?

if u go to an auto service place they can add an ultraviolet dye to your cooling system. then u can use special glasses to easily see any leaks under blacklight. shouldn't cost more than $20

i had this done to my a/c system but it can also be done on the coolant system.