'02 Impala 3.4L, 185k: Running HOT!

'02 Impala 3.4L, 185k: Running HOT !

Full Disclosure: This thing has had a coolant leak for a few months now, and without both time and energy to get to it, I’ve been just filling with mostly water, but enough coolant to prevent freeze damage (although this car is in the Carolinas where freezing is not much of an issue). Leak seemed to be coming from firewall side of engine, but I haven’t been able to determine exactly where. Water sometimes comes down like a waterfall with more than one stream, but then other times, it doesn’t appear to leak at all! Really weird.

Anyway, while I was away for 10 days, wife claims car “overheated” on a short 2 mile trip to place where she runs. “Overheated” means engine temp went to the far right, but she shut off the engine and never saw any “steam” coming out of engine compartment. Car had plenty of water in it at the time.

So I just checked it out and here’s what I found:

1.) On short neighborhood test drive, Engine temp rose quickly to 225 F.

2.) Popped hood and heard loud “SHHHHhhhhhhh” noise coming from cavity between Alternator and Power Steering Pump, but couldn’t see any obvious liquid leaking anywhere. Top of engine does have sooty ‘blemishes’ on aluminum intake, which is something that seemed to be getting more noticeable lately, but that’s it. Also some damp stains on “V” seal on side of block where intake gaskets are, but no liquid oozing out.

3.) LOW COOLANT Message appearing in cluster, but this might be dirty sensor (seen this before). But this was also symptom of intake gasket failure previously.

4.) Radiator cap reasonably clean underneath. No ‘sludge’ or ‘muddy’ residues.

5.) Top radiator hose got HOT during short drive, but bottom hose was STONE COLD. This means bad radiator, right?

6.) Intake gaskets replaced in May 2008 @ 104,980 miles. I used Felpro ‘metal-framed’ gaskets, also replaced all lifters, all disturbed o-rings (injectors, fuel rail, coolant bypass, oil pump drive, t-stat housing pipe), both valve cover gaskets, T-Stat, plugs, wires). Re-used old intake bolts, using blue threadlocker.

7.) Engine sounds and runs OK otherwise.

8.) Plenty of water in overflow tank.

9.) Radiator was replaced 4 years ago, Nov 2010, (Advance Auto, ReadyRad) at 140,700 miles. Might be able to get 1 free replacement if it turns out it has failed internally.

"Top radiator hose got HOT during short drive, but bottom hose was STONE COLD. This means bad radiator, right?"
A collapsed hose (internally) or a cavitating water pump will cause he same symptom.
You might want to flow test your radiator and your water pump. By the way, I’ve never seen a replacement radiator guaranteed for four years, so as much as you might hope to get the problem paid for on someone else’s tab, I wouldn’t count on it.

Water sometimes comes down like a waterfall with more than one stream, but then other times, it doesn’t appear to leak at all!
My money is on the heater core. Bypass it and see if the problem disappears.

10.) Computer Codes: P0102, P0442

I am absolutely leaning towards the lower intake gaskets on this engine

They are NOTORIOUS for that

The location of the leak seems to point in that direction

That code could also be caused by an intake air leak, which is, technically speaking, unmetered air

Per your point #6 it sounds like you did everything right, especially using the Fel-Pro metal based intake manifold gaskets. That’s what I used on my 2002 Malibu. In that paragraph you stated you changed the thermostat, but that was seven years ago. With a hot upper radiator hose and a stone cold lower radiator hose it seems like you’re getting no circulation. I would change the thermostat. I’ve never seen a radiator so plugged that the lower hose wouldn’t be at least luke warm.

Head gasket.

What do you think of this (for a pressure test)?


Would this work well enough, or should I purchase something more substantial?


I think that radiator came with an LLT which at Advance means ONE free replacement, but I’d have to check. On second thought, though, I don’t think it’s going to be the radiator. Leaning toward air pocket right now. Need to do pressure test, it sounds like. But when I do this, isn’t this just going to reproduce the hissing leak except with the engine off? And won’t I just be pushing out the existing air bubble and introducing a new one?


Yeah, hoping it’s NOT that, but this would still be better than “insightful’s” suggestion: Head gasket! I think maybe the intake gasket has blown a leak under extreme heat. Could be the head gasket, but it sounds higher than that to me. Could it be that the gasket is still OK, but the Permatex seal has blown? This car hasn’t been driven anywhere for any extended length of time, and there’s never been any steam coming from under the hood.


How about a big air bubble? Could that stop coolant flow? It seems like the T-Stat is opening because the upper hose got hot, but not so hot that I couldn’t hold my hand on it indefinitely (but then, the car wasn’t driven very far to GET it very hot).

@ColtHero‌ The thermostat may not be stuck completely shut. You may have a trickle flow coming through which would allow the hose to get really hot, especially when the engine gets overheated. With a trickle flow passing through the radiator it may be able to cool it way down.

And yes, you may have a big air pocket somewhere. Bleeding these off can be really tricky. Sometimes you have to get creative. The last time I changed the coolant on my Cavalier I had an air pocket that I couldn’t get rid of. Opening the bleeder screw didn’t help at all. I ended up pulling the small hose off the coolant recovery tank (the one that goes to the engine, not the radiator). I stuck a funnel in it, held it high and low and behold (glub glub) I got another quart or two in it. That solved everything.


Maybe running pretty much 90% water in the system the last few months has damaged the T-Stat? Going to do a pressure test and go from there. May try to burp air out first, but not holding out much hope there

In a properly operating cooling system the upper hose should be hot and the lower hose should be cold. That means the radiator is doing its job properly. But inadequate circulation can do the same thing. Low circulation due to a bad water pump will really aggravate the problem because the coolant spends so much time slowly going through the radiator that it gets a lot colder before getting to the lower hose.

I think you are going to find a bad water pump here.

Colthero, I’m not sure I understand your post, but bypassing the heater core would not cause another air bubble. You bypass the heater core by disconnecting both heater hoses and either placing a splice between them (a piece of copper of aluminum tubing will work fine) or “jumping” the two spots that the hoses are connected to with another piece of hose, taking the core out of the system. You do need to purge the system after installing the bypass, as you do any time you open the system.

Water intermittently “coming down like a waterfall” between the engine and the firewall sounds very much like the seam where the intake our output attachment pipe connects to the heater core is failing… There is absolutely no doubt that there are other possibilities, but that’s a common one.


I just replace the water pump last June at 182,932 miles. That was the 2nd replacement since factory. First replacement went in in July 2006 when the weep hole started leaking after a 900 mile drive to New England. Same thing happened this last time, too … weep hole leak. So I’m thinking the pump is probably OK. The radiator was also replaced November 2010 (that was 1st replacement since factory). I might’ve jumped the gun on the hose temperatures. Maybe I just felt it too soon. Top hose WAS getting hot, bottom was cold, and I immediately thought blockage, but maybe not. Might’ve been too soon to check.


I think I mis-characterized the “waterfall”. Apparently what’s happening is it appears NOW (after pressure testing with Advance “MasterBuilt” kit, that the very bottom of the front cover is leaking. This steady stream of fluid falls into the box frame support underneath, then comes out various holes, giving the appearance of a “waterfall”. This leakage is nowhere near the firewall, and the heater core hoses look fine (and dry).

Using the rented cooling system pressure test kit ($250 YIKES !!), even though there were 18 adapters, NONE fit the pedestrian Impala radiator neck (unbelievable) !! But the UNIVERSAL worked, and was able to pump it up to 14+ lbs (cap = 15 lbs). It actually held there pretty good, if not for the steady stream of fluid coming out the bottom !! After about 3-4 minutes, pressure was down to 6 lbs.

Can someone verify via attached pic that this is the front cover leaking?

The front cover doesn’t hold coolant, so it would not be leaking. Something behind it could be leaking though such as a freeze plug. It is hard to tell from that picture. It looks like one of the front bottom corners of the block, but it doesn’t show the trail of coolant or the source. I’m sure if you could see that, you would know where your leak is.

Do you have rubber or plastic covers on the inside of your wheel well that you can remove to inspect the front of the engine? This might help if you do.

Does this engine have a coolant crossover, at the front of the engine?

You could try some UV sensitive dye designed for this purpose. The kit comes with a blacklight. You simply add the dye to the coolant per the instructions, run the engine (in your case just until the leak starts), then look with a blacklight. The trace will glow.

The photo is great, and I tip my hat to you, but I was unable to tell anything from it.

I’m going to disagree about the timing cover not holding coolant. In fact the water pump is mounted in the timing cover, it has to hold coolant, and it travels through the timing cover into the engine block.

But the leak could also be from the front of the intake manifold gaskets. Get under the power steering pump and alternator with a mirror to take a closer look.

Yeah, it’s hard to see exactly where the coolant is coming from. When looking from the passenger fender from above, there’s just too much stuff in the way and no matter where I shine a flashlight I cannot see anything leaking anywhere. I just see this steady stream underneath falling to the ground and when I look up from underneath I see it coming from the bottom corner of the block.

Keith - good suggestion with the wheel well! I forgot about that! Should’ve thought of it because I just replaced the front cover gasket on my '97 Taurus last March and had to remove those plastic covers during that job. In the case of the Taurus, coolant was coming out of the seal at the top left corner. With that car, coolant does flow through the cover, and the water pump is embedded in the face of the cover, but with this Impala, the pump sits pretty high up and in front of the engine (more toward the radiator), not embedded in the cover like the Taurus, so I’m not sure yet if coolant flows through the cover (like the Taurus).


I’ll give the mirror a try, but it’s so congested over there that I’m skeptical I’ll be able to see anything. From what I can see, though, it doesn’t look like the intake gaskets are leaking. There’s some dampness along the “V” seal, sure, but nothing that would cause a steady stream way down below like I’m seeing. I can also see some dampness on the driver’s side “V” seal, too.

I’m going to pull those wheel well plastic panels off first. That might give me a straight-line view of the area of leakage. Or, the leak could still be behind a pulley - like the crankshaft pulley.

Hopefully it’s not the timing cover gasket because it does appear to have a couple of coolant ports in it.

The only things that can leak at that corner of the front of the engine are the head gasket, timing cover, and the intake gaskets. The water pump is mounted into the timing cover. I think if you pull the alternator you should be able to identify the source of the leak.

OK - I’ve got some glacial ‘progress’ to report. Before ripping anything apart, I decided to do a compression test today. Figured it was good information, right? Keep in mind that this engine starts right up and runs like a clock with no unusual noises (other than the hissing and water seepage noises coming from between the alternator and power steering unit at the very top of the engine, which I’ve yet to find the source of):

Here are the compression test results (BTW: each cylinder was ‘cranked’ for about 5 seconds, and each pressure was timed for at least 5 minutes afterwards to see if it held):

Front side (Right To Left):

Cylinder #6: 185 lbs/in2, and held solid

Cylinder #4: 190 lbs/in2, and held solid

Cylinder #2: 185 lbs/in2, and held solid

Firewall side (Right to Left):

Cylinder #5: 185 lbs/in2, and held solid

Cylinder #3: 190 lbs/in2, and held solid

Cylinder #1: 180 lbs/in2, but seemed to leak very slowly down to 175 lbs/in2 after about 1 HOUR

So - what does this mean? Is my head gasket probably OK? I was worried about cylinder #1 - that’s why I did it last, and was surprised to see the pressure reading seemingly OK. Although there does seem to be some leakage there, does this warrant a head gasket job?