Low Coolant Light Warning

[NutNbutGMC]

A plea for suggestions, if I may?

I have a 2000 Suburban, 5.3L engine. Two hundred and twenty thousand miles. Been a great vheicle.

The dang low coolant warning light comes on every so often and it is driving me nuts.

Sequence of recent events:

A while back, light comes on, check reservoir, add fluid, and go on about my business.

A few days later warning light reappears. Shucks. Add more coolant. Fluid is going somewhere.

Took it to a radiator shop. Replaced water pump after a radiator guy (local business) said he saw it leaking a bit. Also checked all hose clamp fittings for tightness, etc.

Light reappears again in a few days.

A week or so later, the Mrs. rear-ended another vehicle at low speed and had front-end damage. Radiator was replaced due to the accident damage. I think the coolant sensor is in side of the radiator but I may be wrong. My thought is the sensor should be good.

While at the repair shop / body shop, a GM mechanic there diagnosed bad head gaskets (of which I suspected). What else could it be (I am thinking)?

Had the gaskets replaced.

The Mrs. called this morning on the way to church... low coolant light returns..... She's mad and I'm going nuts.

Any suggestions please?

[NutNbutGMC]

Light did not return on the way home for her.

Resevoir is low.

Dang it.

[Robyn]

Does the truck have a rear heater unit or lines that could be leaking and not showing??
Radiator- Replaced
Head gaskets- Replaced
Hoses ??????????
Water pump Replaced
Front heater core?????
Going into the engine, any signs of coolant mixing ?????

There is not many more places that can leak coolant

Missy

[rustyk]

The low coolant could just be the result of air bleeding out of the system. Bring the level up and see how it goes.

[NutNbutGMC]

Does the truck have a rear heater unit or lines that could be leaking and not showing??
Radiator- Replaced
Head gaskets- Replaced
Hoses ??????????
Water pump Replaced
Front heater core?????
Going into the engine, any signs of coolant mixing ?????

There is not many more places that can leak coolant

Missy

Thank you Missy for the additional checklist. I'm on it this evening.

Hoses are good. The front heater core has not been checked. I do have rear heating but have no visible leaks.

I do indeed keep a piece of cardboard under it while looking for leaks. Dry as a bone.

No signs of fluid mixing into the oil. I have changed it twice looking for this specifically.

[NutNbutGMC]

The low coolant could just be the result of air bleeding out of the system. Bring the level up and see how it goes.

This is the second time I have heard this in as many days. This goes on the checklist of the few remaining areas of possible causes. Thank you.

[NutNbutGMC]

Came back on today.

Could there be a crack in a head or engine the block, leaking the fluid to an internal destination?


This one is fixing to go to the scrap yard.

[NutNbutGMC]

I'll take it in tomorrow for a final verdict.

[NutNbutGMC]

Diagnosing. Will know something tomorrow.

[spoolinstyle]

Any updates by chance?

[NutNbutGMC]

Left it in the shop today with a GM Tech. They pressure tested it, checked the rear heater, front core, visual (not disassembled) on the heads (again) and no leaks. They drained the oil and it was not contaminated (where I suspected an internal leak by way of a cracked head or block, even though the head gaskets were just replaced and one would have thought to make that visual inspection at that time). No leaks on the ground (concrete floor), no damp or wet carpet from a heater core, no leaky hose connections, and no idea.

Nothing.

They scoured that entire enclosed system. The contention was that the last warning light may still be attributed to said air pocket in the system. Their next plan is to replace the resevoir tank (where the sensor is located) if the warning returns. My point to them is that when the light comes on, sure enough, the fluid is low.

Bottom line is that the Tech took the truck down off the rack scratching his head wondering.

I am replacing about 1/4 - 1/2 gal of fluid each time (which spans across about a week's time). The fluid has to be going somewhere. If it is leaking externally, I do not see it or smell it. Internally, the oil is clean.

Thanks for asking. I'll stay on this as time progresses. May be another week or so until the fluid drains down again, or it may be purged of air this time....

[NutNbutGMC]

The Mrs. called today from her travels. She has heard (from within the cab) a recurring gurgling sound. Her hearing is impecable. She says the light will be coming back on soon.

[NH2112]

What I'd do is find out the total cooling system capacity, then drain the system completely by whatever means necessary (back up on ramps or a hill, remove block drain, etc.) Measure what comes out, add coolant to bring to proper amount if needed, then pour it back in. Until every drop that's supposed be in there IS in there, you won't be able to accurately troubleshoot the problem.

[NutNbutGMC]

What I'd do is find out the total cooling system capacity, then drain the system completely by whatever means necessary (back up on ramps or a hill, remove block drain, etc.) Measure what comes out, add coolant to bring to proper amount if needed, then pour it back in. Until every drop that's supposed be in there IS in there, you won't be able to accurately troubleshoot the problem.

Certainly not out of the question at this point. Thank you Sir.

I am still waiting on the light. I am betting that it will come on while she is driving to church tomorrow...

[hatzie55]

Certainly not out of the question at this point. Thank you Sir.

I am still waiting on the light. I am betting that it will come on while she is driving to church tomorrow...

If the Mrs is hearing gurgling inside the cabin you have air pocket(s) in the heater(s).
Does it gurgle when you think the system is full or does this happen after the coolant level has dropped? Air pockets can actually damage the heater cores over time.

Is the Radiator cap new? Is the spring center closing and sealing properly? Are the sealing lips on the tank or radiator free of burrs. If the cap is not sealing it will bleed out coolant and let fresh air in with the coolant.
If the cap isn't new get a new one, back-flush the entire system, then completely empty it including the block drains. Blow out the heater cores with no more than 5 PSI air.
When the fill cap is on the radiator I clean the rust and crud out of the overflow bottle with CLR and tons of water.
I usually make up 4 gallons of 50/50 distilled water and coolant mix so I have a known concentration to work with.

1) Place the front of the truck and radiator top significantly higher than the heater by using ramps or parking it on a very steep hill. This will force air to the top of the cooling system which should now be the rad cap. Double check that you in fact have the rad cap side of the radiator slightly higher than the rest of the cooling system. If the cap is on a reservoir then you may have to un-bolt/clip and hang the reservoir reasonably level to achieve this.

2) Turn the heater(s) to full heat and the directional controls to the floor. Turn the fan(s) to medium speed.

3) With a stone cold engine only... Open the bleeder on the thermostat housing if your engine has one. Fill the empty cooling system all the way to the top with a 50/50 coolant and distilled water mix. Keep filling till the level stops dropping or coolant flows from the bleeder ( you can ignore the HOT level on the tank for now ). Close the bleeder and cap the cooling system with a new Stant spring center cap.

4) Start the engine and block the accelerator pedal at a high idle of 1500-2000rpms. Uncap the cooling system. As the engine warms up the thermostat will open, the top radiator hose will abruptly get warmer, and the coolant level may drop. Start adding more of your 50/50 mix of coolant and distilled water until it is right up to the top of the radiator fill neck or a 1/8" or so above the HOT fill line on the separate tank. The coolant level will drop and you may see air bubbles coming up as coolant displaces air in the heater core(s). Continue for at least 10 minutes... longer if air bubbles can be seen or the level keeps dropping. Don't worry if small amounts of coolant mix burp out the fill neck, you can rinse this off with a hose when you're done.

5) When no more air bubbles can be seen or the coolant level is not dropping for more than 5 minutes, re-install your new Stant spring center rad cap then unblock the accelerator pedal. Don't drop the revs till you cap the system.

6) Verify that you have filled the system with "at least" the published amount of coolant.

7) Check the level on the bottle when you return the truck to a level surface. The radiator should be completely full and/or the tank will be filled to the HOT level or just above . If it's below the HOT level top it off to just above the HOT line. If it's significantly overfull there may be a little more air in the system. If it's showing overfull I'd take the truck for a 50 or so mile run in hilly terrain to slosh the air out. Make sure to keep the RPMs up above 2500 for the entire run and the heat in the hot positions with the fans on medium. This should push coolant everywhere it should be and dislodge any small air pockets.

8) If it's gurgling again after your maiden voyage or reading low drive it back up on ramps or the steep hill used in step 1, top it off with 50/50 mix starting at step 4, then take it for another run.

[NutNbutGMC]

Thank you very much. Currently it is still an issue. I'll jump on this, this coming Saturday. Thank you Sir.

They replaced the resevoir and sensor this past week.