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Unique-ish Cooling Issue on my GTP?

S

sambroom

New member
First, I absolutely SCOURED the internet and read up on everything and anything I could regarding the symptoms my 1999 GTP has. I could not find anyone with the same combination of symptoms as my car. I have only had this car for a few weeks, and I immediately went through basic maintenance.

Me: I am reasonably mechanically inclined, but I am not a certified tech, so there are definitely holes in my knowledge and ability.

The Car: 1999 GTP with 188k miles, bone stock except a 180 T-stat I put in. I bought it 3 weeks ago, so history is a mystery. It has a upper-end ticking noise at startup that goes away within one minute. I’m thinking lifter/tappet oil drain on that.

Here is the spread of symptoms that are keeping me up at night (maybe related?):

Smell of hot coolant under hood when warmed up (no visible leaks or puddles)

Engine runs hotter than I think is normal, especially with a 180 T-stat. It usually stays steady at 2-3 marks below the 210 line on the dummy gauge, though it climbs above that if I drive up long hills in 90 degree+ weather. I had to turn around and head downhill the other day because the temp got too high for comfort (3 marks above the 210 mark on the dummy gauge, I stopped and turned the engine off and opened the hood to help it cool. When the engine was off I could hear boiling coolant in the overflow). That night I tested the cooling ability by running the engine at 3000 RPM in park for a few minutes. The fans come on at about the 210 mark, but if I keep the RPM at 3000, it seems like even the fans are insufficient to bring the temp back down while stationary or uphill at low speed. The temp kept climbing until I stopped my test when the gauge reached 2 marks above 210 and rising. So yesterday I flushed the whole cooling system (ran the car for about 30 minutes with the heater blasting, feeding water into the radiator and letting it drain out the plug at the bottom, occasionally revving it), I drained the water, and put in fresh coolant, a new 180 t-stat and radiator cap, took a 20 minute drive and bled the air out through the valve on the t-stat housing. I have re-bled it a few times with the engine hot, and there is NO AIR. Radiator level under the cap looks good. I tested the cooling ability again today, but got the same results. The engine can’t cool itself under load without significant airflow.

So my worries are the following:

Lower intake Manifold Gasket?
Head Gasket?
Water Pump?
Clogged CAT?

Here are some of the other tests I have done so far:

Oil level looks good, and is clear. No “milkshake” look from coolant in the oil
Exhaust is clear and smells normal. No noticeable coolant burn smell or white smoke
Took the radiator cap off and checked for bubble while running, there were none
Checked the cooling system for pressure first thing in the morning. There was no pressure
No hint of oil in the coolant that I can see
Heater in the car blows good and hot when the engine is warmed up

Other than the cooling issue and the mild startup tick, it starts up and runs smooth.

To help eliminate head gaskets as suspect, I am going to compression test tonight.

So what do you think? Am I expecting too much of this car wanting it to go up hills during the summer? What about the smell? Without the presence of coolant in the oil and exhaust, could the intake manifold or head gaskets still be suspect?

Also, what are some of the other symptoms of a clogged cat? If the water pump is quiet and not leaking, can I assume its ok?
 
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First off, have you cleared out all of the dexcool sludge already and changed the lower intake manifold gaskets to the metal ones?

Next would be water pump, the sludge can actually destroy the fins on one and then it doesn't really pump anymore.
 
coolant issue sounds normal. the cluster gauge is worth less. you need to scan the temp via the obd2 port with the torque app or some thing of the likes to know what its really reading.

the coolant smell tho. you need to look into that. water pump can leak, the plastic elbows can leak as well, the heater hoses to the fire wall can leak too.

if you smell it in the car, then the heater core is likely leaking.

the ticking is a lifter. gm says its ok if goes away in a minute or two. oil change can help clear it up. mine would tick if i went past 3,000 miles on a oil change. change the oil and no more tick on cold starts. this engine had over 200,000 miles on it too.
 
Check between the cylinder head and intake manifold, see what color the intake gasket is. If the color is still black, then it's possible that the LIM gasket have not been done and that the cooling passages are blocked up from previous use of old dexcool coolant.

Other things that leak are the coolant elbows, they may not drop puddles on the ground but they are super common to leak and cause the coolant smell.

Water pump fins could be gone too, they wear away from corrosion with old dexcool.

If you had a head gasket failure this motor would overheat way faster, have white smoke from the exhaust.
 
Yeah I forgot to mention. It had dexcool in it, so after the flush I put green peak in, because of all the recommendations online that I do so. I'm not sure if the LIM has been done... it has black silicone visible, but it looks more globby in the corners than I thought the manufacturer seal would look... So that's still a question mark.
 
that's the RTV used to seal the valley gaskets, we are talking the gaskets between the LIM and the heads. they would either be black hard plastic or aluminum.
 


ah yeah. I'll take a closer look at the transition to the heads tonight. I think black though. I was looking for evidence of new LIM gaskets the other day
 
if you look at the lim bolts, they are in a deep well, if those bolts are covered in black fluid. its time to do the lim gaskets, thats coolant thats seeped up the threads of the lim bolts.

one of my out side edge bolts under the egr, it used cry when the engine was al warmed up. left a nice trail.
 
Wow this forum is great! Thanks for the quick response.

coolant issue sounds normal. the cluster gauge is worth less. you need to scan the temp via the obd2 port with the torque app or some thing of the likes to know what its really reading.

the coolant smell tho. you need to look into that. water pump can leak, the plastic elbows can leak as well, the heater hoses to the fire wall can leak too.

if you smell it in the car, then the heater core is likely leaking.
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I'll check the elbows and hoses tonight... I don't think the temp gauge reads accurately, but in the conditions I mentioned, it was definitely rising with no indication of leveling off, and the engine was definitely getting too hot (boiling coolant). Neither my 05 corolla or my 95 F150 get so hot running the same road. I'm going to go ahead and pull the water pump and check the fins too.

if you look at the lim bolts, they are in a deep well, if those bolts are covered in black fluid. its time to do the lim gaskets, thats coolant thats seeped up the threads of the lim bolts.

one of my out side edge bolts under the egr, it used cry when the engine was al warmed up. left a nice trail.
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I'll check that and the gaskets between the heads and the LIM too...

Honestly, if I can determine that the cooling issue is from the LIM gasket, its a non-issue for me, because ultimately my intention with this car was to build it a bit. If I do, I will inevitably have the LIM off at some point anyway. But before I launch into all that I really want to get everything running well, or at least be sure the engine is healthy and worth upgrading... If not, I want to sell it and get another one. If I can get it running and cooling flawlessly, and when I have the spare cash, I'm thinking higher ratio rocker arms, new lifters, tune-in-a-box PCM, 3.5in pulley and downpipe. So to do the lifters I would have to pull the LIM anyway... even if I left the stock lifters in, I might as well pull the LIM when I do the rocker arms... So, assuming the compression looks good tonight, if I could be pretty dang confident the issue is the LIM, I would go ahead and buy all the parts for my mods (when I can afford them), and just take care of it while modding. Any reasons why my plan my be stupid?
 
you'll want more than just a downpipe for the exhaust... If you can find a front PLOG that would be fine, or go with some cheap Speed Daddy headers, maybe 220-ish on ebay. They come with a down pipe anyways, and if you got a way of welding you're set.
 
Front PLOG eh? I wondered about headers, but I figured if I was only doing the 3.5 pulley (and not going for a drag racer, just a bit more get-up-and-go) I thought the downpipe would move enough exhaust... Evidently that is not a good idea? If I went the PLOG+DP route, why would the PLOG only be needed for the front? does the rear exhaust manifold flow better? If the headers include a DP for $220 sounds like that might be cheaper than a PLOG+DP anyway.

But as far as the cooling issues, does it seem like I can safely limit my worries to either water pump, LIM Gasket (or associated blockage)? Or need I look into other potential factors?
 


water pump and LIM gaskets are your main concerns, you will want to change out the coolant elbows for aluminum while you're in there. You should do a flush as well, there's still probably some sludge lurking around in there somewhere.

And the factory front manifold sucks balls, rear is tubular instead of cast iron. and headers can cost up to $850+ for good ones.
 
WarStryker13 said:
water pump and LIM gaskets are your main concerns, you will want to change out the coolant elbows for aluminum while you're in there. You should do a flush as well, there's still probably some sludge lurking around in there somewhere.

And the factory front manifold sucks balls, rear is tubular instead of cast iron. and headers can cost up to $850+ for good ones.
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Sounds like a plan. I'll look over the LIM tonight for indications that it is leaking coolant, and whether it has been done or not; compression test; and pull the water pump to see if the fins are worn bad. $850 happens to be what I paid for the car lol! Not going in that much for headers. I will look for a used front PLOG, or cheap headers though.
 


I can reach the holes, but I cant turn it enough, or even align the threads with that big bulky hose on it. I've been at it for over an hour and I'm about ready to give up on the back three... front three read dry 1:120, 3:125, 5:132

so, so far the biggest deviation is under 10%. I wish I could get at the back three, but I'm tired, and the engine is cooling to the point I wonder if I'll even get a consistent read. all the plugs looked the same, and a healthy dry reddish color at that.
 
You could use a pry bar to angle the engine forward slightly, if you disconnect the front dogbones you can get it even further.
 
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