98 Tahoe losing coolant intake manifold questions help!!!

nygacr95 · #1 03-15-2005, 10:14 PM

Okay, I found this site yesterday, and found it quite helpful. I have a 98 tahie that has been losing coolant for a while now. I decided to pull the intake off today, (what a job!) and see if I could find any leakage. (I replaced the radiator cap previously, no signs of external leakage, the replies point to intake manifold gaskets) I cannot determine if my intake manifold gaskets are the culprit. Does anyone know what I should look for? I am considering taking the heads off, since I am this far down. The tahoe ran pretty much normal the whole time I had it (about a year) and it has 88,000 miles on it, 350 vortec. Any help would be appreciated! I would prefer to not take heads off, if they don't need to come off. I could smell coolant while it was idling, and when it was shut off, if it is any help. Thanks!

SpitAndDirt · #2 03-16-2005, 08:38 PM

If you already have your intake off, you need to replace the gaskets anyway, there's no reusing your old ones. You will just have piece of mind that they have been replaced now. Just make sure that all of your mating surfaces are clean and free of pitting so that coolant doesn't find it's way around the new gasket.

dramey_2004 · #3 03-16-2005, 08:46 PM

The best thing to do (yesterday) is to pressure test you cooling system with a coolant manual pump. At this point your best bet would to be to pull the spark plugs out make sure you pull them all and look at the electrodes to see if the are a white ashy color. good luck

nygacr95 · #4 03-16-2005, 09:34 PM

Update... I pulled the plugs today, the machine shop did not have my intake done (broken coolant fitting, which I heard is real common with these manifolds) All of the plugs looked the same, the porcealin (sp) was a nice mocha tan where the plug was indexed, the electrode (l shaped thing) was soft powdery gray, typical of a normal running engine. All of them looked good. I am not going to pull heads now, I am going to just fix the intake and put it back together. I guess sometimes you got to roll the dice. I did pick up a cap and rotor, since mine are horrible looking, figured since it was this far down, might as well replace them. Any other advice would be greatly appreciated, especially on timing, can this be done with a timing light? I marked the distributor, as the haynes manual said to (the factory manuals are a bit more complex, IMHO, and heavy...) and it seems there is a mystery in timing...

dramey_2004 · #5 03-17-2005, 02:17 PM

Hey good thing you marked the distributor when you put it back in hopefully you have not turned the engine over at all or you will have to line up the rotor button so it is pointing towards the #1 plug wire fitting on dis. cap and have the #1 cylander all the way up on the compresion stroke. Just let me know if you need a detailed discription. But hopefully you havent turned your engine over any and just lock the distributor down where it was you can not do any timing adjustments on this vechicle your ecu will advance or retaurd the timing. let us know

nygacr95 · #6 03-18-2005, 09:52 AM

well, the intake is on, That's all the further I got... I guess I got the flu or something. I did not move the engine, and marked the distributor at all, so I should be good. I am impresses that the ECU can set the timing as such, pretty cool. You guys have been of superb help! I think what makes this job so bad, is all of the wiring that you have to maneauver around. BTW, did anyone else have to sit in the engine bay on more than one occassion? (haha, I did, and I am 6'7" my gosh) I just hope I got everything sealed up real well, I used a lot of acetone to make sure it was all clean and followed the instructions of sealing around the water outlets on the head side. I really hope this is the final chapter on this intake... I miss driving the tahoe...

glenncof · #7 03-19-2005, 11:11 AM

1997 Tahoe - 118K miles

Yea, the intake leaks are a "feature" of this engine. Using RTV as sealant with thin walls and streching bolts ... it is surprising they last as long as they do. Common failure here is defined as nearly 100% I would guess.

I have other suggestions. Change front oxygen sensors. Life expectancy is 100K miles and gas mileage drops off ~10% on mine.
www.thepartsbin.com Bosch 15703 $44.67 each.

Another suggestion is replace spark plugs. GM says replace at 100K. You already have done cap/rotor I believe. Those lasted until 100K. Plugs were still servicable at 100K but replace with authentic GM plugs (Do Not Use Substitions.) I got at dealer for $42. I think that's OK for 100K miles.

nygacr95 · #8 03-19-2005, 09:50 PM

More updates... Okay, got it all back together today. I originally changed plugs about 10,000 miles ago, but my buddy had a set of plugs left over from his 97 he never put in. I installed them with a new cap and rotor, (even a new fan belt) hooked everything up, and it seems to be running okay. Give it a couple of days, and we will see if we lose anymore coolant. My only problem I had was my oil pressure guage read like 130 lbs, and never zero'd. I swore I hooked everything back up, and low and behold, how I even manged to unhook it in the first place is beyond me. I hooked it up, and it took care of everything. It seems to run fine, and I will be taking it to work in about half an hour. (give it a real road test) Thanks for all of the help! Funny thing is I was checking my parent's 98 for routing and some hook-ups, and their's has the early tell tale signs of the same problems...

CHARLENE MCGHEE · #9 05-23-2005, 04:35 AM

Quote:

Originally Posted by nygacr95

More updates... Okay, got it all back together today. I originally changed plugs about 10,000 miles ago, but my buddy had a set of plugs left over from his 97 he never put in. I installed them with a new cap and rotor, (even a new fan belt) hooked everything up, and it seems to be running okay. Give it a couple of days, and we will see if we lose anymore coolant. My only problem I had was my oil pressure guage read like 130 lbs, and never zero'd. I swore I hooked everything back up, and low and behold, how I even manged to unhook it in the first place is beyond me. I hooked it up, and it took care of everything. It seems to run fine, and I will be taking it to work in about half an hour. (give it a real road test) Thanks for all of the help! Funny thing is I was checking my parent's 98 for routing and some hook-ups, and their's has the early tell tale signs of the same problems...

Well - did this seem to fix it, or do you still have the leak? Whats the latest update?

nygacr95 · #10 05-26-2005, 03:32 PM

Well, I guess I need to check the coolant, as i haven't checked it for several weeks. I topped it off last time, it took maybe 16 ozs, if that, and before that it was the same, about two weeks before that. (I checked the coolant twice, since I did the repair) I can tell you this, THe Tahoe runs a ton better, it has way more power, andthe gas mileage greatly improved, but this might have been somewhat due to the temperature change. I am now getting right around 15 MPG and I was getting 10.5 or so. (I check regularly...) Keep in mind, I put new plugs in, and a cap and rotor. (although the plugs only had 10,000 miles on them, I got a free set from a buddy that were never used...)

All in all, it seems to be good. I think the worst part of the repair was access to the back of the engine, placing th intake back on the engine, and of course, working around the wiring harness. Everything else was real straight forward, if you got the tools, and some pretty decent know-how. If you are confused at changing oil, or brakes, maybe you should consider paying someone to do it.

Thanks again to all of you on the forum that helped!

Best!
RIck

Imcgyver · #11 07-31-2005, 05:47 PM

Great info but I have not seen the timing specs, here they are the timing is +-2 degrees cam retard if it is not in spec the computer will throw a code of having cam retard out of limits. a scn tool will help but remember to shut the engine off to reset the cam retard once running turning the disrtibuter will not change the reading on the scan tool.

Spicoli · #12 08-02-2005, 09:19 PM

In all of that I don't know if I got the jest of it. What was the fix? New coolant fitting?
Where is it on the manifold?

nygacr95 · #13 08-03-2005, 08:54 AM

Okay, more UPDATES....

Tahoe is running great. Once about a month, I top it off with about 8 oz of coolant. I figure this is an air bubble or pocket working it's way out.

As far as timing goes, I was not under the belief that there was timing adjust on this series of engines, unless you tap into the brain of the great computer. The distributor engages the cam in one specific location, the same as where it is removed, and the computer sets the timing from there. When you remove the distributor, make sure you know exactly where it came out so as to return it to the proper spot, the computer does all of the rest. So I guess you can spin the distributor all you want, you're not going to change the timing spec, as far as I know... (and that seems to be the thought of the 98 Chevy 1500 series factory service manuals... )

As far as what actually fixed this thing, here is what I found. THe intake manifold gaskets were blown/leaking, whether minor, or major, i was loosing coolant, and pulling the intake and putting on new gaskets solved the problem. The coolant fitting, located on the right side towards the front of the manifold, has a quick release, and it looks like it was made of pot metal, or some softer alloy. It was corroded and easily broke off, when i tried to remove it. THis is common to have these break, and they are readily available at you local autozone, or chevy dealership.

I hope this additional information was helpful. I will keep answering questions, as they come up. It really wasn't that bad of a project, looking back several months now....

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