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Coolant Questions. Low Coolant Sensor is Intermittent

TheBude

New member
18
5
3
Buick Ownership
2001 Century
2000 Century Custom, 90k miles.

Wanting to know exactly where the coolant level should be inside the radiator. Should it be filled to top of radiator neck? Should it be about one inch below the cap or neck?
Aso what temperature should the coolant be at operating temp.

Low coolant sensor light is intermittent. Previous owner replaced intake gasket a few months ago. I've read some forum posts that state oil in coolant from intake gasket leak can cause residual oil to coat level sensor causing it to become faulty. Any suggestions?
 

chem_man

Buick Newbie
28
6
3
Fallston, MD
Buick Ownership
1999 Century
The radiator should be completely full. Also, the coolant reservoir located on the passenger wheel well should have a hose connecting it to the nipple on the radiator neck just below the radiator cap. Also there are cold and hot levels marked on the coolant reservoir. If it is not filled, it should be filled to at least the cold level. I keep mine filled to about midway between the cold and hot levels.

Regarding your intermittent low coolant indicator light, I would check to make that the plug is fully seated into the sensor. Also, I would unplug the connector first and make sure that the contacts are not corroded. If they are only lightly corroded, get some CRC electrical contact cleaner and spray the contacts and then plug and unplug the connector several times to clean the contacts up a bit. FYI, the coolant level sensor is located about 1/3rd of the way down the engine side of the radiator on the passenger side of the radiator and it is below the automatic transmission oil cooler line.

Your 2000 Century should run between 195 - 205 degrees Fahrenheit when fully warmed up.

Good luck!
 

MelsRegal

Full Member
3,969
507
113
Buick Ownership
Regal GS 2017
On a completely cold engine the radiator should be full and the coolant recovery tank should be at the cold level or half full.
Normal operating temperature is 195 to about 225.
Check the sensor and see if it is coated.
 

TheBude

New member
18
5
3
Buick Ownership
2001 Century
Thank you chem_man.

if you are willing to, hopefully you can answer another related question.

The person I purchased it from recently is a trusted friend. He replaced the intake gasket (as mentioned previously) and did a coolant drain and fill + bleed as well. When he sent me pictures prior to buying the car one picture showed the rad-cap off and the radiator filled to the top with (green dye) coolant. I checked the coolant level today and it was down an inch or more from the top. The reservoir is between low and full line.

I am not sure what method he used to bleed the coolant. He is very mechanically inclined so my guess is he did it per service manual. There are no external leaks so I'm a bit concerned coolant may be leaking into the cylinders possibly through a head gasket breach or possibly not tightening the intake gasket bolts to proper inch/pound spec.
I told him concerned (or paranoia..lol) but I didn't want to question him to intensely as it may appear that I am scrutinizing and I don't want to come off like that. Anyway, any thoughts please?
______________________________
 

chem_man

Buick Newbie
28
6
3
Fallston, MD
Buick Ownership
1999 Century
OK on your observation about the coolant level in the radiator being about an inch down. Not too bad - a good drive will get things hot enough and then as it cools down, the radiator will draw in coolant from the coolant reservoir/overflow tank. Also OK on your friend using the green antifreeze.

Just as an FYI, the orange colored antifreeze better known as Dex-Cool, got bad reputation because of intake manifold leaks in the 3.1L, 3.4L, 3.8L, and other engines. The leak that happened was not the fault of the antifreeze, it was the fault of the polymeric/plastic materials some design engineers at GM picked to use in the intake manifold gaskets. The gaskets degraded in the presence of ethylene glycol based antifreezes. After the intake manifold gaskets began to leak, better intake manifold gaskets were developed and the problem vanished. However, there is one "difficulty" so to speak with Dex-Cool, and that is if the cooling system is not completely sealed to air, some gunk will form due to a chemical reaction, and this junk or crud, often collects around the radiator cap. GM did redesign the radiator cap so it would seal out air much better. I am currently unsure of the new part number but a search on google should be able to find it. Also, do not mix the green antifreeze with Dex-Cool.

If I were in your shoes, I would top off the radiator as best as I could with 100% antifreeze, and then put the radiator cap on and bring your coolant reservoir up to the full hot line using more 100% antifreeze. Then drive around in order to get the engine good and hot, and then park it where you live or can work on the car. Let the engine run, roll down the windows and turn the heater on and move the temperature selector to hot and let it run for another 5 to 10 minutes. After the 5 to 10 minutes, open the hood if you have not done so already, and using the appropriately sized metric socket (assuming you have one) loosen the air vent on the metal heater hose line that comes out of the engine and makes 90 degree bend. You will want to loosen it very slowly praying that it does not shear off inside the larger brass fitting. Hopefully it is not seized and as you continue to loosen it, you'll soon have some air spit out followed by antifreeze. There is also a 2nd air bleed on top of the thermostat housing at the other end of the engine. Carefully loosen that one as well in order to bleed out any trapped air. Be sure and tighten both screws down firmly, but not like a gorilla. If one or both break, you can purchase new ones at most any auto parts store. They are made by Dorman, and the part number is 902-112. They are normally sold two to a box.

Now you can turn the engine off and let it cool down for several hours and then check to see if the coolant level in the coolant reservoir dropped any. On thing I would also do is to make sure all the hose clamps on the upper and lower radiator hoses are tight (not gorilla tight, but tight) and that all the hose clamps on the heater hoses and the bypass hoses around the base of the throttle body are also tight (again, not gorilla tight). Your friend who did the work might have missed a hose clamp or two when he was putting everything back together. I know I did when I replaced the lower intake manifold gaskets on my 99 Century this last summer. I caught the loose ones when I went back over everything and double checked my work.

Now comes my big recommendation. If you plan on doing any of your own maintenance, be sure and purchase a Haynes Manual for your Buick, It will be invaluable to you in that it has lots of pictures and step-by-step instructions on how to do things like changing your own oil, doing your own brakes, how to troubleshoot things, etc.

Regarding whether or not your friend properly torqued the lower intake manifold bolts or the upper manifold bolts can be checked rather easily using an appropriate torque wrench (in-pounds or foot-pounds). Advance Auto Parts, O'Reilly Auto Parts, and AutoZone all have loaner tools that you can use by leaving a monetary deposit when you check out say a torque wrench or a ball joint press. You can then look up the appropriate torque specification in the Haynes Manual and then check a couple of the outer lower intake manifold bolts for proper torque. When you return the tool, you get your deposit back.

Be sure and check the oil level in the engine to make sure that it is not increasing due to antifreeze leaking into the crankcase. Also, observe the dipstick carefully and make sure there is not anything like a chocolate milkshake clinging to it above where the full level indicator is on the dipstick. Also look at the bottom of the oil fill cap. There should not be any of that chocolate milkshake stuff there either. HOWEVER, if you live in a cold climate, and the majority of your driving is short trips, some of that chocolate milkshake stuff is considered normal because the engine does not really get hot enough for long enough to completely boil off the moisture in the air that gets trapped in the engine and then condenses onto the oil and mixed up with it.

I don't really think you have a bad head gasket or a loose/leaky lower intake manifold bolt. But it is possible, and that is why I have given you all this information so you can check and hopefully rule it out. If all else fails, some auto parts stores can recommend a test kit that you can use to see if there are combustion gases in the antifreeze, or you can get an oil analysis performed by a laboratory such as Blackstone labs by requesting a sampling kit and sending in a couple ounces of oil that you drain from your engine and requesting a test for antifreeze. NAPA also sells a kit for that where you send the sample into Wix Filters and they have a lab analyze for lots of thing - fuel in oil, wear metals, etc.

I know this is a lot to digest, but take things one step at a time and you'll soon learn if you do or do not have a major problem. Plus, remember, there are a lot of people on this forum who have a great deal of experience to assist you, Just spell out the problem, answer our/their questions, be patient and you'll get some guidance/advice/answers to your questions.

Good Luck!
 

TheBude

New member
18
5
3
Buick Ownership
2001 Century
Thanks again chem-man. Great info.

I think it may have an updated rad-cap...looks like this one: 2000 Buick Century V6 3.1L (8th Vin Digit J) Radiator Cap

I just filled the reservoir to the high mark with green (all make/models) pre-diluted coolant and also filled the radiator to the top. It required about 3 or 4 cups of coolant. Engine oil was just below low mark on stick and my friend said oil was changed 2k miles ago. Took one quart to get it to high mark on oil stick. No milkshake appearance. I will bleed it per manual soon.

I've done block tests on cars before and know they are accurate only if blue test fluid turns yellow or green denoting exhaust emissions in coolant. Though a negative block test doesn't disprove some types of head gasket breaches it's a good place to start. I may do a leakdown test on it when I get a chance.
 

TheBude

New member
18
5
3
Buick Ownership
2001 Century
At which point on dash temp gauge should the radiator fan(s) engage? During bleeding the coolant with front end on ramps, heater on Max heat + fan on 3, the dash temp gauge rose to one bar past halfway point. Is this normal level on temp gauge if the engine is idling for 20 minutes or more?

I hear a clicking noise but the fan hasn't engage. I turn the engine because I didn't want an overheat.
A waited a couple hours, added coolant (less than a cup) to full and then drove it for 20 minutes. While carveas in motion the temp gauge never rose past 1/3 mark . Got home, idled it for 15 minutes and temp needle went up one line past half for a few minutes and then dropped back down to halfway and just below halfway. Is this normal?
 

TheBude

New member
18
5
3
Buick Ownership
2001 Century
I forgot to add that heater worked great inside the cabin the entire time.
______________________________
 

Waiex191

Active member
208
74
28
Poplar Grove, IL
Buick Ownership
2000 Century
My coolant light was on. I got a sensor from the junkyard and then it was good.

White smoke from the exhaust is a sign that coolant is getting into the combustion chamber. I had that on mine when I got it. It was a barn car for 5 years and maybe the gaskets dried up. The seal for the coolant passage was busted and it must have been sucking that in through a leaky intake seal. I replaced it with a fel-pro gasket and now it's good.

For cooling fans check out this thread including links:
https://buickforums.com/forums/threads/2000-century-cooling-fans.53346/

Here is my thread:
Another new member with a 2000 Century
 

chem_man

Buick Newbie
28
6
3
Fallston, MD
Buick Ownership
1999 Century
I'm not sure at what temp the cooling fans come on, so thanks to Waiex191 for the link.

Regarding your temperature gauge, I am not sure if your gauge is funky or if the engine coolant sensor is funky. Do you have a scanner that can monitor real time data such as engine temperature? Also, do you have access to an IR temperature gun? My 99 Century's temperature gauge is always showing ~200 Deg F (and verified using an ODB bluetooth dongle and BlueDriver on my Android phone). I do know that the 2000 Century uses a 195 Deg F thermostat. Sounds like this is something you might want to look into.

Regarding the clicking you heard, it could come from a number of sources such as the EVAP system canister purge solenoid or the AC compressor.

FYI, Waiex191 is sort of an expert on repairing the Buick Century. He and his sons rebuilt one and posted about it in great detail, and as a result, he has a great deal of excellent information on how to do things! Thanks Waiex191.

Good luck!
 

TheBude

New member
18
5
3
Buick Ownership
2001 Century
Thanks everyone for the replies so far.

To clarify the bleed procedure I used: I put the car on ramps ( rad neck higher than cylinder head) and bled the coolant by (at cold engine) opened the bleed screw and added coolant via radiator until the bleed screw hole pushed coolant out (displacing air with coolant) and coolant filled to top of radiator neck. I then tightened the bleed screw closed.
Next, with the rad cap still off and climate control set to max heat + fan on 3 (4 not working) I ran the engine with from cold to operating temp, held a rev occassionally (at operating temp) and filled with coolant as needed. At one point with revving (not past 2k rpms) I could see air bubbles and then some coolant gushed out of the radiator. I shut the engine off and about 10 minutes later added coolant again to top of radiator and bleed screw. Started it and let it idle or (bleed screw closed/ rad cap off) for 20 more minutes. Filled the reservoir full and radiator full. Let it sit overnight and checked both the reservoir and radiator the next morning. The radiator was full and the reservoir looked to be a bit over the full mark.

Just drove the car from south Florida to north North Carolina yesterday and it ran well. Low coolant level light flickered about three hours into the drive so I shut off the engine and opened the rad cap (with a rag, standing back, and halfway first for a minute to relieve pressure. Removed the cap fully and fluid was all the full to top of radiator neck. I pushed and wiggled the low coolant sensor with my fingers, pulled on the connector wiring and then put the rad cap back on. The low coolant light has not come on since. After arriving home in NC the engine cooled overnight and I checked the coolant level in the radiator before driving the car. The coolant level (cold level) was down to the base of the radiator neck. The reservoir level is about an inch over the max mark.

When I turn the a/c on the radiator fan engaged. During the 12 hour drive yesterday the temp gauge stayed steady at the first mark above cold mark on dash gauge. Here's a thread that seems to say that my car's temp readings are normal: 2000 Coolant temp - how high is too high?!

I just purchased a BAFX Bluetooth obd2 scanner and plan to use it tomorrow and will post results.
 

Waiex191

Active member
208
74
28
Poplar Grove, IL
Buick Ownership
2000 Century
You will like that scanner. They are great.

I bled my coolant system on the ground, engine running, using the bleeders. That was the procedure I had found online.

Thanks chem_man for the positive feedback!
______________________________
 

chem_man

Buick Newbie
28
6
3
Fallston, MD
Buick Ownership
1999 Century
TheBude, OK on how you bled the system. According to what you wrote regarding your trip, it sounds like all is well with the cooling system, and that you don't have a leak. Also sounds like you may have fixed your intermittent low coolant light.

I have 2 of the BAFX bluetooth scanners and as Waiex191 said, you will love it! I use the Torque Pro app and it has made my life much easier in tracking down misfires! I love being able to monitor engine temp, long term fuel trims, transmission temp, engine load, etc., while cruising down the road.

Waiex191, you are quite welcome. Just telling it like it is!
 

TheBude

New member
18
5
3
Buick Ownership
2001 Century
Waiex191 and chem_man great replies so far...thank you.

Today I found an external leak (could have been there since I purchased it?). I can't see where it's emitting from, only where it drips from. It's dripping from the far left hand (driver's side) bottom of the radiator near a round rubber piece. It's such a slow drip that when watching that area from underneath the car for 5 minutes I only saw two drops hit the driveway. Hoping it's not the radiator but confirms coolant loss and better than an internal leak. I'm going to get it looked at tomorrow. With the old Honda Civic's I've owned (and other various cars) in the past 10 years I did all the repairs but it's a bit congested in that area of the leak and I'd like to get it up on a rack and second pair of eyes (and hopefully experience) to pinpoint it.

The BAFX scanner is reading well with an app named "Car Scanner" I downloaded. Radiator fan engaged at 223 degrees without having to turn on the a/c compressor. It may need a new thermostat as the current one may be stuck open? How long should it take to open and at what temp (195 F)?

Yesterday after work the transmission started hard shifting from work to home (15 minute drive).Today, it's shifting correctly. I've read this is somewhat of a common issue and is usually the pressure shift solenoid. Also a Transgo shift-kit may help along with new filter and fluid drain and fill. I'm even considering using Seafoam Hydra Trans-tune to clean out varnish deposits about 100 miles before changing ATF. I usually don't but into that kind of stuff but there are many good reviews only. However, all opinions and suggestions appreciated.
 
Last edited:

chem_man

Buick Newbie
28
6
3
Fallston, MD
Buick Ownership
1999 Century
OK on finding a small drip. If I had to guess, you are talking about the radiator drain petcock. I think it uses a 1/4 inch drive socket extension to remove. You might want to get a replacement - I know that Dorman has one. And, yes, the drip could have been there when you purchased the car.

Congrats on getting a BAFX OBDII dongle! I use one with Torque Pro, and I love it! One can monitor lots of engine parameters with it.

My 99 Century gets up to temperature (195 Deg F) fairly quickly - 5 to 10 minutes in cold weather if I had to venture a guess. If your thermostat is stuck open, I believe that it would take quite a while for the engine to heat up and you would notice that your heater was not putting out hot air. If you do decide to change the thermostat, you will need a special wrench like the ATD 3310 GM Thermostat Wrench in order to remove the thermostat housing bolts. If you don't have the tool, you'll need to remove a whole lot of parts in order to get at the bolts! Here is a link to the wrench - Amazon.com: ATD Tools 3310 GM Thermostat Wrench: Automotive

Regarding your rough transmission shifting, I would not use any cleaner additives in the transmission. I would do a pan drop drain and filter change and refill the transmission with 6 to 7 quarts of Dexron VI. Then after driving 500 to 1000 miles, I would drain the AT fluid in the pan again and refill using another 6 to 7 quarts of Dexron VI. Let the fresh Dexron VI do the cleaning for you. Also, consider purchasing an AT oil pan that has a drain plug in it (Dorman has one and they are under $30 from rockauto.com) as it will make doing fluid changes much easier (and less messy). The only additive I would add to the transmission fluid is LubeGard Red at the recommended rate of 1 oz LubeGard Red per quart of ATF in the system.
 

TheBude

New member
18
5
3
Buick Ownership
2001 Century
Frisbee: Yes, confirmed same car.

chem_man: After I posted my past reply I looked at oem radiators to check for prices in case that's the issue. The pics shows the drain plug in the area of the leak so I am with you that the drain plug (o-ring) may be the issue. I reached up to tighten it and it I couldn't tighten it any farther by hand. The video below shows the gentleman using a 21 mm socket on the drain plug. I'll find a socket and try tightening it today.

The thermostat takes about 10 minutes to get too 195 F and it's been in the 30's-40's in my area in the mornings. Heat is working decently. It doesn't ever stop putting out heat but it seems/feels like it could be hotter than it gets currently.

Any experience with the Transgo shift kit? Amazon.com: 4T65E Transgo Shift Kit: Automotive I've used Lubegard Red in a 1998 Honda Civic EX before and while I can't say it helped it certainly didn't cause any issue. That generation Civic EX a/t was known for hard shifts even when new....wasn't a harsh/hard shift, just really firm.

 

Frisbee

Member
50
26
8
OK, now that I know that the same vehicle is being discussed, it raises the next question: Just what model year is this Century? The thread I linked in my post above says "2002", your status block (to the left of each of your posts) says "2001", and the 1st post in this thread (as I write this) says "2000"! o_O

If your thermostat is stuck open, you will probably be seeing DTC P0128 ("Coolant Temperature Below Thermostat Regulating Temperature"), but (initially) only in colder weather. In warmer weather, the MIL (Malfunction Indicator Lamp) will eventually go out (after 40 "trips" without the PCM sensing that condition, IIRC) but that P0128 code will remain in the PCM, quite evident if you regularly scan for codes like I do.

Here's a post I made that's very relevant to P0128 (on any GM vehicle), but also has some useful general advice.

Did you scan for codes with your new scantool setup yet?

Nobody has commented on this, but your coolant temperature gauge seems too low compared to what I typically see on Buicks of this era! The dashboard gauge usually stays near the half-way mark in my experience.

Also, FWIW, I too am happy with the BAFX Bluetooth scantool. I don't use it nearly as often as my wired (USB) scantools, but I found it to be quite capable and a good value.
 

TheBude

New member
18
5
3
Buick Ownership
2001 Century
OK, now that I know that the same vehicle is being discussed, it raises the next question: Just what model year is this Century? The thread I linked in my post above says "2002", your status block (to the left of each of your posts) says "2001", and the 1st post in this thread (as I write this) says "2000"! o_O

If your thermostat is stuck open, you will probably be seeing DTC P0128 ("Coolant Temperature Below Thermostat Regulating Temperature"), but (initially) only in colder weather. In warmer weather, the MIL (Malfunction Indicator Lamp) will eventually go out (after 40 "trips" without the PCM sensing that condition, IIRC) but that P0128 code will remain in the PCM, quite evident if you regularly scan for codes like I do.

Here's a post I made that's very relevant to P0128 (on any GM vehicle), but also has some useful general advice.

Did you scan for codes with your new scantool setup yet?

Nobody has commented on this, but your coolant temperature gauge seems too low compared to what I typically see on Buicks of this era! The dashboard gauge usually stays near the half-way mark in my experience.

Also, FWIW, I too am happy with the BAFX Bluetooth scantool. I don't use it nearly as often as my wired (USB) scantools, but I found it to be quite capable and a good value.
I made a mistake it's not a 2002, it is a 2000. No CEL's and while driving it today from cold to operating temp and monitoring the temp with the scanner it shows temp up to 195 F within 7 minutes of driving and 215 F after 10 minutes. Tops out and fan comes on at 225 F at idle for several minutes after reaching operating temp.
 
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