98 Cavalier 2.2L overcooling

Hi all - new to the forum, but have gotten some great tips here over the last year or so I figured I'd post with a problem I can't seem to solve.

Here's the problem:

I have a 1998 Chevy Cavalier 2.2L wit A/C.

In September, I noticed that the coolant bypass pipe (black metal pipe) leading from the upper rad hose to the engine was leaking at the welded elbow. I went to the GM dealership, got a new pipe and o-ring, and replaced the pipe (fixed the leak). When I replaced the pipe, I also had to remove and install the temperature sensor (no problem) and also flushed the rad out and refilled with a (approx) 60/40 Dexcool/water mixture. I made sure to bleed the cooling system to get out any air bubbles using the bleeder screw on the heater core pipe.

On the drive home on the highway, I noticed that the car ran cooler than it had previously. My car usually ran with the temperature gauge just shy of 90 degrees celcius (about 190F - halfway on the gauge). On the highway, it ran somewhere between the quarter tick mark (halfway between the 40 and the 90) and the 90. I figured that I had flushed some dirt into the thermostat and it was stuck open.

Fast forward to the end of October/November - it's getting colder outside. The car would warm up to 90 in stop and go traffic, but once the car was going down the road for an extended period of time without stopping, the temperature gauge would drop down to the quarter tick mark, and creep back up once I was stopped for any length of time.

I changed the thermostat (twice - the first one Motorad and the second from NAPA - both 180F opening temp., just like the original) but that didn't completely solved my problem. I then changed the temperature sensor, and the car now holds temperature - halfway between the quarter tick and the 90 degrees celcius in the city, and at the quarter tick on the highway).

I always have plenty of heat to the cabin - far more than I need actually, so I believe the heater core to be functioning properly - the intake and outtake pipes are both warm.

I tried putting cardboard in front of the rad, but that does nothing.

Here's what I noticed going on under the hood - after a good long drive, all the hoses are warm except for the lower rad hose going to the thermostat - that's cool to cold.

Other Cavalier owners I know in the area have their car operate at a constant 90 degrees.

I've read through the forums here and found this, but this doesn't seem to answer my problem:
http://www.automotiveforums.com/vbulletin/t498689.html


Any advice would be more than appreciated! Thanks in advance!

What I would do is go get a thermy from Gm. I have read were on ocassion aftermarket thermostats are just crap. Seems odd that with rad blocked off it still runs cold. on a side note I just changed coolant on my recently puchased firebird and I also noticed that it runs cooler . It has since been winter stored .will have to check it in spring

What I would do is go get a thermy from Gm. I have read were on ocassion aftermarket thermostats are just crap. Seems odd that with rad blocked off it still runs cold. on a side note I just changed coolant on my recently puchased firebird and I also noticed that it runs cooler . It has since been winter stored .will have to check it in spring

Well, I originally replaced the first thermostat with the Napa version because of threads I read here about how bad some of the replacement thermostats were - apparently Napa uses Stant thermostats, which are considered very good.

Still no luck though - the only thing I can think of is perhaps the new coolant is absorbing more heat??? :screwy:

I'll play around a bit more and see what I can come up with - any other ideas are always welcomed!

Thanks again.

Call me a dummy... but if you have good heat in the cabin, then what is the problem with the engine running cooler? I'm just wondering, because if i had this 'problem' i probably wouldn't think anything about it. Is overcooling truly a problem?

Call me a dummy... but if you have good heat in the cabin, then what is the problem with the engine running cooler? I'm just wondering, because if i had this 'problem' i probably wouldn't think anything about it. Is overcooling truly a problem?

Yes, consistent overcooling can cause damage to the engine, not to mention unneeded gas consumption as the car continues to run in the closed loop cycle keeping the RPMs higher in order to bring the car to temperature.

Also, the on board computer needs the car to be at operating temperature so it can fine tune the car properly for maximum efficiency.

I had checked under the hood while the car was running the other day, and the radiator fan was not running. I was hoping I was missing something as simple as the fan being stuck on...no such luck! :banghead:


This really has me stumped because a cooling system in a car isn't made up of that many moving parts - mostly just pipe, a water pump, a thermostat, a radiator, and a heater core....and some valves and sensors.

Here's a little more info on what I've noticed - The car almost never gets out of the closed loop when it's cold outside now (below 32 F or 0C) - my idle RPMs are still somewhere between the 1000 RPM and 700 RPM mark - my car idles at 650 RPM when warm. This tells me the car's sensors are showing that the car is cold, and needs to warm up.

Another bit of oddity with the cooling system is that there is a film on the inside of the windshield that looks like fog but won't go away - when you clean it with a rag, it's like dirt/grease.

Also, even after bleeding the coolant system, when I go to push on the gas going in drive for the first time of the day (or when the car is completely cold), I can hear a "gurgling" or "water running" sound like there's air in the system somewhere (most likely I can hear only the heater core, because that's the only cooling system component in the cabine, and it's very audible). This sound is MUCH less than it was before I replaced the thermostat and re-bled the system, but it is still there nonetheless.

Here's what I'm thinking - I've read on a few automotive forums that a blocked, or partially blocked (or partially air locked), heater core can cause overcooling - nobody can figure out why this is, but flushing the heater core usually solves the problem. Given that I can hear a "running water" sound when the car accelerates (and there's initially very little pressure in the system and the water pump is building pressure), I'm thinking one of two things - either the rad cap on the coolant reservoir isn't holding the 15 psi pressure when the pump isn't working, and thus not holding the required pressure at all, or there's a tiny leak in the heater core (causing air to enter the system (really BAD for DexCool I hear; and causing that greasy film on the inside of my windshield from the defrost vent venting onto the windshield).

I really can't see how either those would cause an overcooling condition since you'd think that they would cause over-heating (either not having enough pressure in the system to avoid boiling the coolant, or having a block/partial block of the heater core causing the coolant to not circulate fast enough to cool down sufficiently).

All the symptoms sort of point to an open thermostat, but the lower rad hose connected to the thermostat is cold - like no warm coolant rotating through it (even after it comes through the rad it would at least be warm!). The pipe that goes across the thermostat at the t-junction is warm on both sides of the thermostat...so I reckon that it's just not hot enough to open up the thermostat to allow the coolant to circulate in the open system. Also, thinking this through, the pipe that goes across the thermostat comes from the outlet hose of the heater core.

Any thoughts would be greatly appreciated...this is just so frustrating because it's like I'm missing something so simple.

Well, a new development - today after my drive to work when I shut down the car, I heard a glugging sound, like a drain not properly vented or a pop bottle being poured too quickly. It was very loud - do you think it's the heater core that's gone?

Thanks for the help!

Quick update - finally broke down and brought the car to a GM dealership - spent $200 on "diagnostics," 3 road tests, and I don't know how many times explaining myself. They acknowledge that the temperature is bouncing around (one temp when city driving, a significantly lower temp highway driving), but 1) don't see the need to do anything about it - "it's not overheating, so your fine," and 2) can't think of what might be wrong. They did find some air in the system, and had to "reverse fill" the system from the upper rad hose to get out all the air.

I even spoke with the shop forman who said that "it's not worth tearing up the car over."

The day after I got the car back, I drove to the store, shut the car down, and heard a loud bubbling...for like a full minute!

Can anybody think of what might be causing this?

I just read your post and I've had the same problem (in the same car). Mine started after I had to replace the water pump and drained most of the system. (about 2 years ago). I get the same overcooling problem, same water gurgling, but i don't have heat at any speeds above 40 mph. which makes my winter commute interesting. I haven't been able to figure it out either, 1 water pump, 3 thermostats and a couple of bleeds later. No one who I’ve talked to who has owned a cavalier has experienced this, and I've gotten no answers or results in anything I’ve done. Sorry I don't have any answers or suggestions, but it's nice to know your not alone with a problem sometimes. Good luck, and your not crazy for wanting your car to run right.

Yet another update in this never ending saga! :banghead:

I replaced the water pump and the rad cap - also tore into the dashboard and had a good look at the heater core (zero evidence of leaking). I'm still overcooling - only getting between the quarter and half way mark, and then falling again to the quarter mark if I'm not stopping with any regularity!

I'm also still hearing the gurgling sound after shutdown (only sporatically though) and hearing running water in the morning when I accellerate for the first time (only). There is also no evidence of coolant loss.

Please help! I need to pass my emissions test soon, and having it constantly in the high idle will not help me to pass!

take it back to your Gm garage where they say all is fine then tell them to pass the emissions test on it. Maybe ask what brand of thermy Gm uses , whether it is Stant or not

i can understand the worry over not reaching proper engine temp, but after reading your posts i didnt read if the check engine light was on. the reason im asking is that i also have caviler, a 96 that was brought in with the check engine light on. the code was for the engine not reaching proper engine running temp within the correct amount of time and drive cycles, so it never reaches open loop. so i changed the thermostat only to find that the previous owner had removed the stat but put back in the thermosts plate. so afer i replaced the thermostat, bled system, topped her off she would over heat in 10 minutes while idling or driving. so i replaced the raditor thinking that i had restriction, so after bleeding, and topping off it still overheats just takes longer, around 15 to 20 minutes wether driving or idling. so im looking to replace the water pump next(any help in this area would be gratfulyy appreciated). so the reason i was asking about the check engine light being on is that if there isnt MIL light set then the ECM doesnt see a problem. just like the GM techs didnt see a problem, there relying on a code to help them in there diagnostics rather then accept that there might be problem. like a sensor failing within range, so id check the coolant temp sending unit to make sure im actually getting the correct temp reading at the dash, since the ECM might be getting a different reading from the coolant temp sensor.

Yet another update - brought the car to a proper mechanic and not those yahoos at the GM dealership - he did a block test right in front of me...C02 detected - slow head gasket leak causing an air lock around the temp sensor from expelled compression. New head gasket being installed now.

A lesson to all you car guys out there - you know your car, and if you know something isn't right, don't let some tech tell you otherwise - find a good mechanic - he's worth his weight in gold!

I'll let you know if this solves everything.

Thanks to all who replied with great suggestions.

that is a new one to me, a bad head gasket causing overcooling, usually its the opposite

so how much are they going to charge you to do the head gasket??

my car runs really cool as well. usually about 1/4 and when idling it creeps up slowly. it never goes over half anymore but it used to overheat really bad and we discovered it was the fan motor. my old boss's mechanic said he "fixed it" but since then it's run cold. so i have no idea why. and when it's cold outside, it'll stay at or close to zero.

That bubbling your hearing is often your fuel return line gurgling. I've heard the same thing before after i've shut my car off and pin pointed it to that.

Yet another update - brought the car to a proper mechanic and not those yahoos at the GM dealership - he did a block test right in front of me...C02 detected - slow head gasket leak causing an air lock around the temp sensor from expelled compression. New head gasket being installed now.

A lesson to all you car guys out there - you know your car, and if you know something isn't right, don't let some tech tell you otherwise - find a good mechanic - he's worth his weight in gold!

I'll let you know if this solves everything.

Thanks to all who replied with great suggestions.Hmmmmm just wondering if this solved everything or if someone got peeled..........lol

Hmmmmm just wondering if this solved everything or if someone got peeled..........lol

Well, muff34, the answer to that question is both yes and no - the car did have a head gasket leak - I saw the gasket when they took it off - hairline crack between the cylinder and the coolant sleeve. The head was also very warped due to the over-heating that wasn't being detected. The head was machined, and a new Felpro gasket installed. The car runs a thousand times better than it did before - quieter, easier starting, better power and fuel milage.

That said, we've (the mechanic and myself) have had a bitch of a time getting rid of the residual air in the system, and have been bleeding it progressively. Every time we bleed the system, I works better and better, which is telling me that I'm not re-introducing air into the system, but just shifting air from the (very poorly designed) heater core. Who ever heard of a heater core with the lines coming in from the bottom with the core slopping upward creating a high spot for air to get trapped?

So, better, but not altogether fixed...and last week, I also threw as P1336 code (crank position sensor variation not learned) and have to bring it in to get re-learned...sometimes you should just scrap the car while you're ahead - I'm just in too deep now. :banghead:

Well, muff34, the answer to that question is both yes and no - the car did have a head gasket leak - I saw the gasket when they took it off - hairline crack between the cylinder and the coolant sleeve. The head was also very warped due to the over-heating that wasn't being detected. The head was machined, and a new Felpro gasket installed. The car runs a thousand times better than it did before - quieter, easier starting, better power and fuel milage.

That said, we've (the mechanic and myself) have had a bitch of a time getting rid of the residual air in the system, and have been bleeding it progressively. Every time we bleed the system, I works better and better, which is telling me that I'm not re-introducing air into the system, but just shifting air from the (very poorly designed) heater core. Who ever heard of a heater core with the lines coming in from the bottom with the core slopping upward creating a high spot for air to get trapped?

So, better, but not altogether fixed...and last week, I also threw as P1336 code (crank position sensor variation not learned) and have to bring it in to get re-learned...sometimes you should just scrap the car while you're ahead - I'm just in too deep now. :banghead:So the over heating was not being detected because of the air in the system??? Ya hear ya about being in too deep,they can nickle and dime you to death. sounds like this one is more like loonies and toonies........lol. Thanks for the reply ............interesting.