Low Coolant only when cooldown startup

02 Impala 3400 71K radiator flushed and dexcool replaced with "Complete" a dexcool compatable product last fall. I have NO Coolant Loss whatsoever, No overheating. Read through thread searches and cleaned LC sensor. the result was it was a bit dirty, cleaned, put back in solved problem of light staying on all the time. Now the light comes on at cool start then goes off as engine reaches Operating temp...system was properly bled at bypass and thermostat. Again no coolant loss nor performance issue. My thoughts are that it is either a bad pressure cap or the thermostat is malfuntioning of which the latter does not make sense to me due to proper operating temps. Heater works as normal airconditioning also working normal. Again NO Measured coolant loss over two week period 1000 miles. Radiator is full when cap removed cold....normal warm up when cap left off and light goes out....at op temp....

littledave~

What brand coolant did you use? I noticed over the years some members have complained about the low coolant indicator not working properly after switching coolants like from Dex-cool. Including after replacing the level sensor. I don't recall any resolution to the issue either although a lot of us do not get the problem. Must be some kind of variable. Some are disconnecting the sensor to get rid of the light but checking coolant levels in the radiator and reservoir monthly.

Just out of curiosity try running a conductivity test. With a DMM on dc volts at lowest scale dip the positive lead into the radiator opening in the coolant only and black lead to battery ground. See what you get for a reading.

Thanks for the response BNaylor, Well the garage that I had the flush done said it was called complete (Komplete)? never heard of it but I figured he new what he was doing as he said it was dex cool compatible...and Biodegradable..all was OK thru winter till I took a 350 mile trip and light came on, on the way back about 200 miles out. Just watched the temp the rest of the way with no rise in temp above 190-5. I don't get any reading on DMM Batt ground to coolant, however do get 13.6 V one side of sensor...I have cleaned the sensor but thinking I need to drain and flush system again as it seams a little cruddy to me. Probably left over from the dex-cool sludge before the flush. this being My first experience with that coolant I didn't reallize it cood turn so quickly...on month it was fine then a month or so later it was sludgy (is that a word?). By the way that is what he told me about the unplugging the sensor but I don't see that as a solution to live with. At this point I am a bit stumped hence search and post here.

littledave~

Decided to clean the cooling system and sensor so I drained the anti-freeze, flushed the block and the radiator+recovery tank. Refilled with water only for a couple of days may put some flush in. But results the same so far...

Yeah sometimes it takes awhile to get all the old Dex-cool and any possible remaining crud/sludge out so a repeated flush is not unusual. About all I can think of is the level sensor?

BNaylor: WOW...I just stopped at the dealer to buy a new cap to start with. Parts guy asks me why? I tell him the story as I did here and he says to me " I guarrantee you it's the sensor gone bad...says he sells 2 a week. Well they're 65 +tax title and first born....I found an ACdelco online for 37+ship so I'll probably go that route....I think you are right and kudos to ya.

littledave~

Update: 6/10/08, put in a new sensor yesterday and so far it's working. I have yet still to replace the antifreeze but I will be using Dex-cool. I understand that I could go with the ethylene glycol Green but want to use original setup when ever possible. It's strange to me that 5-6 quarts are recomended when it only comes in gallon jugs, brilliant. why not a 6-pack!?
Oops, I was thinking out loud, sorry bout' that.

New update: Low coolant level light back on and staying on now...Puzzled? Yeah, I are! I just threw 60 bucks away on the sensor, Argh!

57chevyragtop:

Your intake manifold gaskets are probably leaking. Everything you've mentioned I've already been through with my '02 3.4l Impala. And I started noticing a problem with my car around 65k miles (close to where your mileage is right now). I also didn't think I was losing coolant, and my car wasn't overheating either (and it was running perfectly fine). But over a longer period of time (months), you'll probably see that the coolant level drops and you'll have to keep adding fluid.

When you pulled out the radiator sensor (which I also did), was it muddy with brown-colored slime around the center post (that you wiped off)? If so, that's oil leaching into your radiator. Check the backside of your radiator cap. Same thing? It's oil in your coolant. You probably DO have enough fluid in your system, but once that center post gets gunked up, the LOW COOLANT LEVEL message appears and it doesn't go away until you pull out the sensor and clean it off.

Check the side of your engine block behind the power steering pump. Look along the diagonal black "V" seal running from the valve cover down to the center of the block. Do you see any damp-looking spotting along this seal? Look down below this seal into the trough formed by the shape of the block. Is it wet and muddy-looking down in there? If so, coolant is slowly leaking out the "V" seal and dripping down into the collected road sand to form the muddy mix.

I monitored my car from 65k to 100k, checking the fluid level often and watching for leaks (adding a bright green dye to the coolant at one point only to see it bubble out the side of the block), until I finally replaced the gaskets about 1500 miles ago. So far, no leaks (block and trough are nice and clean and dry), no LOW COOLANT messages, and no brown sludge on the underside of my radiator cap.

Really sounds like you've got the same problem I had. Three years ago, a guy at an auto parts store told me, "they (GM 3.4L engines) all leak". I didn't believe him then - but I do now. Co-worker is driving a 2003 Impala 3.4L. Guess what? It has the same dampness spotting on the side of the block that mine had. It'll only be a matter of time before the LOW COOLANT message starts appearing on that car, too.

Thanks Colt Hero, I will check that today, and yes I do have the brown sludge you speak of on cap and the sensor. I was hoping against hope for that situation I will repost finding.

Results: Thermostat did the trick, system was well cleaned as well and put in 6 qts of Dex-Cool and filled with distilled water. No Light now. I will admit though it is a difficult part to replace in this engine design. Crossover exhaust pipe cover needs to come off as well as the throttlebody return pipe/heater inlet hose. Getting either back on is just as difficult as removal....So there is my story and I'll stick with it......dave....Thanks all!

OK, but I'll also have you know that I flushed my system too - completely re-filling with the standard green stuff instead of Dex-Cool (I use the "mixes-with-anything" SuperTech stuff sold at Wal-Mart - I think it's actually yellow in color). That was three years ago now. The light came back on anyway.

My guess is the T-stat change had no effect - you probably could've just poured more coolant in to make the light go out.

Good luck! I hope that's the end of it for you, but don't be surprised if it isn't...

Thanks Colt Hero, genuinly understand your point. I have reservation as to the presant fix being the end of it. If I have to tackle the more difficult task of LIM gasket replacement, I'll just have to do so. As far as GM and Chevy product this is definately my last. My 92 Lumina was a much better car and a great deal less costly to maintain. This one has cost more in 3 years than the 92 did in 12 years...Time to sell me thinks!

I went thru the same ordeal with my 3.8L... Wasn't properly fixed until I had the UIM and LIM gaskets replaced...

Funny, but I'm looking at my records right now ... I got my first "LOW COOLANT LEVEL" message at exactly 67,650 miles (on 10/29/05). My annotation says, "message appears for ~ 5 miles at startup only" - which is exactly what the title of your thread says. Surprising to me, but I had actually flushed out the Dexcool at 60,800 miles on 5/30/05 - BEFORE the first LCL message. I remember now reading about theories that the Dexcool was to blame (which I didn't believe), but I got it out of there anyway because it was easy and needed to be done.

Subsequent to this, (looking at my records further) I had to add coolant 8 months later on 6/11/06 at 78,405 miles (~1 Qt!), then again on 11/27/06 at 85,450 miles (~.75 Qt), then again on 2/4/07 at 89,596 (2/3 Qt), 3/11/07 @90,409, 4/8/07 @91,226, 5/10/07 @92,295, 5/29/07 @92,976, then I changed the sensor on 7/5/07 at 93,859 (needlessly, as it turned out), still the light came back ON on 9/13/07 @ 97,495 miles.

Boy, it's really shocking me right now that I added coolant that many times - especially the increased frequency toward the end....

THEN, I finally got the wake-up call: VERY LOUD ENGINE CLICKING NOISE on 3/24/08 that did NOT go away even after warm up. This scared me enough to pour in 8oz of SeaFoam 5 days later at 104,537 miles. Then I finally changed the gaskets on 5/6/08 (the car quieted down enough to allow me to wait for the optimal time, but it wasn't due to the SeaFoam).

I used the Fel-Pro gasket set (~$80), replacing the upper, lower intake gaskets, plus all the other stuff: T-Stat, Oil pump drive o-ringl, plugs, wires, valve cover gaskets, coolant bypass o-ring, injector o-rings, o-rings on fuel rails, t-stat coolant pipe o-ring, but I re-used the original bolts (applying blue threadlocker). Also replaced all 12 valve lifters because the clicking was probably an indication that at least one of them was damaged. Only paid $8/lifter at Autozone (Melling).

You can do this repair yourself if you're reasonably handy. It just takes time. No special tools - unless a low-torque torque wrench, or a Torx ratchet bit are "special" to you. I also ended up buying a 1/4" slim-line ratchet and socket to remove the lower bolt on the T-Stat housing. Even after removing the exhaust cover, it's still really tight getting that lower bolt out! Also bought a 1/4 extension and a deep socket for the bolt at the rear left of the UIM, plus a universal socket to torque the diagonal bolts on the LIM.

Update: 6/26/08...Well guys and gals, It has been a few weeks now and I must let you know the the thermostat replacement and good clean out solved my problem on this. Actually the engine is running better and starting easier than when I bought it three years ago. Gas mileage has improved for in town driving from an avg of 17 mpg to 23mpg. Yes it is hard to get to this thermostat, too hard really....but sure made a difference for my engine.

Again I want to thank all of you for your input right or wrong! It's the participation in the forum that counts. You mean well as you post your thoughts and you make this forum work.....kudos!

Well it's been a few weeks and all is well so far.....Not fully convinced I don't have a LIM gasket problem however. I'll be keeping an eye on the fluid level over next few weeks as I am traveling during that time. I have a gallon of 50/50 mixed going with me but I'll be doing the driving!

Well, it's actually been less than 48 hours since your last post. The leak occurs over several weeks time typically. Then, toward the end, you start losing coolant quicker and quicker.

So - looking ahead to your LIM project - can you do this job yourself, or are you going to pay a mechanic? My Dad just had his Impala done in New England for $528 by an independent. I thought that was a pretty reasonable price. A dealer would've been $1000, most likely...

the last time I was on today I did not see my previous post for some reason, just wasn't there so I was reposting with added thoughts. I will be doing it myself when the time comes. from what I gather the fluid gets sucked into the lower imtake then out the exhaust after combustion in minute proportions at first then gets heavier and performance becomes affected.

Even though the system was apparently "properly bled at bypass and thermostat" you probably did not expel all the air in the system. Even though you used distilled water in at least one of those drain/refill episodes, there is still dissolved oxygen in the water unless you preheated the water to about 180ºF before adding it to the system. Water has an affinity for gasses in air, and will absorb and hold it. Heating that water later (especially under pressure) will liberate gasses and create an air pocket in the system. It may take a couple weeks of heat/cool cycles before the level in the overflow/expansion tank remains constant.

As always, the fluid levels need to be monitored by regular inspection, but the "mysterious loss" of coolant which eventually "fixes itself" is sometimes not really a loss.

Several manufacturers have specifications on the type and quality of water to be used to mix coolant and for top-off. Cummins has/had a very informative section detailing this on their website, and their newer engines are also using an OAT coolant (like DexCool) for the required coolant fill.

I can say that with MY Impala, I never had any performance problems. The car always had plenty of power and never stumbled, stalled, or anything.

However, it DID ultimately make a loud clicking noise ONE day which, as I stated earlier, prompted me to resort to the SeaFoam treatment (which I think did absolutely nothing because the clicking had already stopped the very next day BEFORE I used it).

When I replaced my gaskets, I drew up a pretty nice procedure that I think would allow almost anyone to do the job. I'd say it takes more NERVE than KNOW-HOW to do an intake gasket job on these cars...