99 Alero with 3.4L engineand 130k miles is overheating. I changed the thermostat and waterpump but that did not help. The cooling fans DO come on. The temp gauge moves slowly and seems to be accurate, meaning the engine REALLY does get hot (not a bad gauge or electrical).


Now, the interesting thing to note is that Ido NOT seem to have heat in the cabin (or it is intermittent...comes and goes). This suggests air in the system. I have tried to bleed the air with the little valve on the cooling system and have had limited success. Still seems to overheat.


Other things to note: There is a slight yellowish "sludge" in the upper valve chamber when view from the oil filler hole. I entertained the idea of a blown head gasket but did a compression test and got approx. 160 psi on all cylinders. The engine runs nice and smooth. The sludge may be nothing more than a 130K mile motor.


Right now, I tend to believe that there is still air in the system and it will never run cool w/o proper purging. These engines are unliike any I have ever worked on before. I have never had so much hassle trying to bleed the system. Anyone have a procedure for bleeding the cooling system? Or thoughts as to what else I can try?


An update: add white smoke coming from the exhaust to the list. I can also smell antifreeze in the exhaust. So, happy days, coolant is getting into one of the cylinders. Wonder if that is abad intake gasket? That would explain the loss of coolant. Now, how to check the intake gasket before teardown. Vacuum testing?





Edited by: landar

 

I bet the lower intake gasket is leaking to test it you could try a leak down test...and listen it''s not fail proof but once you get it apart you''ll be able to see it........ the compression test shows that the coolant isn''t leaking into the cylinder at the headgasket which is why i say the lower intake gasket

 

Well you sound like you are very mechanically inclined so a lower intake manifold gasket wouldn''t be too hard for you. In all honesty it sounds just like a headgasket. I would look right below the throttle body and the power steering pump for a leak on the block. If you see it in those two places its an intake manifold gasket.


To bleed the air from the cooling system you will need a 2 foot long peice of clear hoses, 1/4in id. With the system cool fill the over flow tank to the full level. Now pull the little plug out at the air bleeder. Put the hose over the bleeder and run it to the overflow tank. The cap needs to be off. Now start the car and put the heater all the way on with the fan on high. Watch the the level of the overflow tank and fill as needed, and watch the temp gauge. When everything warms up coolant will start to come into the clear 1/4in hose. Let the car run till the bubbes stop coming up the hose. I have a hood prop so i zip tied the clear hose to it instead of the overflow tank, that way the air bubbles excape easyier. I didn''t have any coolant come out of the hose till I shut the motor off and even then it was just a little bit. Hope this help you out.

 

Thanks for the replies!


After researching the GM 3.4L engine in the 1999 era, I am almost 100% convinced that I have the dreaded nylon gasket lower intake manifold leak. At least I hope it''s that simple. My worst fear is a cracked block or head.


rusty, thanks for the detailed bleeding procedure. I know exactly what you are talking about and will give that a try. I am interested in knowing why you think this might be a head gasket and not just the intake gasket? Thats why I performed the compression test on each cylinder. If it were a head gasket leak, would you not think that cylinder would show up on the low side (< 100 psi)? I am still open to that being a possibility, just wondering about the logic.


Another interesting note is that one of the new NGK Iridium spark plugs has a brownish colored insulator tip while the others are pure white. I think this shows which cylinder is sucking in the coolant (its one of the front cylinders).


smdepew, I will do a search on leak-down tests and see if that shows anything. You wouldn''t happen to have a quick procedure that you could share, would you?


Thanks again for the replies.

 

Your welcome for the procedure.


The reason I say head gasket is becasue usually when its the intake manifold gasket it doesn''t get coolant in the cylinders. Its usually leaking into the oil or out the side of the block. I could be way wrong though. If you are gonna fix the intake manifold leak I would go one step further and change the head gaskets while your at it.


You said the plug was brownish, take a flashlight and look into the cylinder, as much as you can, to see if you can see the piston. If the top of it looks like rust that where you leak is.

 

I''ll have to look for a write up on it but i have seen quite a few of those intake gaskets break from the coolant into the intake tube as opposed to into the valley area which leads to what your talking about....and besides you have to take off the intake to change the head gaskets so if you get it off and find out it''s not blown out then your not that far from pulling the heads.....

 

Ok, I have removed the lower intake manifold. There is a bunch of slimely, yellow goo on the bottom of the manifold. But oddly enough, the goo is NOT around the lifters or cam. Figure that one out.


I looked carefully at the intake manifold gasket and it is fairly thick and brittle feeling. It also has like a laminated white silicone in it. Looking at the design, I can not see how coolant could get from the water jacket outlets intoan intake plenum. It would have to jump acrossa pushrod that is in-between and that does not appear too likely. No, I would think a bad intake gasket would allow coolant to run onto the top of the cam and into the oil pan. But, I dont seem to have any coolant in the oil. I should mention that when I removed the 8 manifold bolts, I found that one (drivers side, nearest the firewall) was already loose. So, it could not have been doing its job. All of the bolts were drenched in engine oil.


That leaves the (gulp) next most likely scenario: Bad head gasket or cracked block/head. BTW, this engine is the biggest PITA that I have ever worked on! And I have dealt with a few. (Sorry for that little rant. I feel better now[img]smileys/smiley17.gif[/img]).


Do you guys see any way that a bad lower intake manifold gasket would allow coolant to get directly in a cylinder to be burned? There is no mistaking the white exhaust smoke and smell of coolant being burned. Or,despite the good compression test, does this indicate bad head gasket?Edited by: landar

 

My guess is still blown head gasket. I have read and read all about the lower intake manifold gasket failures and have never heard of the coolant going into one of the intake runners, not to say its not possible.


How hot would you say the motor has gotten? When my head gasket blew my temp gauge got up to the 3/4 mark or a little higher. I never had the heads or block checked, just put new gaskets in and its been good to go ever since.


Have you gotten any service engine soon lights yet?

 

The engine service light did come on at one point and the code was "cylinder #2 misfire". The motor temp usually fluctuates between slightly abovehalf and full.


I also do not see how coolant would go from the water jacket hole to an intake runner so I am going after the head gaskets.


What puzzles me is that the compression showed fairly even and the engine runs nice and smooth. I guess a slight crack that opens up when the engine heats up. Next, I will remove the front head (that is cylinder #2) and see what it looks like. Thanks for the info. I also need all the moral support that I can get! This aint fun. [img]smileys/smiley18.gif[/img]

 

Yeah that sounds exactly like when my head gasket went, and it was the #2 cylinder also.


I dug this up for you.


http://www.grandamgt.com/forum/showthread.php?t=68087&hi ghlight=intake+manifold


One thing to watch for is the o ring on the inlet line to the fuel rail. If it tears or gets lost GM is about the only place you can get it, its some weird off size.


Hope this helps you out.


One more thing, get a manual if you don''t have one. GM has changed some of the torque specs over that last few years. I would recommend trying to get a torque spec sheet from GM.Edited by: rustyballs_69