Chevy 5.3 Coolant issue

[dhermesc]

I just bought a 2002 Chevy 1500 with a 5.3 engine (about 95K on the clock). The previous owner said that the "low coolant" light had been on the entire time they owned the vehicle(2 years) - but the coolant wasn't low. The day before I test drove the vehicle the expansion tank (reserve tank) had been replaced - he said they couldn't replace just the sensor - it was part of the tank. I test drove and bought the truck. About an hour of driving it the "low coolant light" came on. Parked and checked and it was below the half mark (full when cold line) about an inch or two. Very carefully removed the cap and the expansion tank backfilled to the "full" line when the pressure was relieved. I went ahead poured a little less than a quart of coolant into the expansion tank (overfilling it some) and drove it 6 more hours without issue.


Most people say the tank gets fuller under pressure - this one appeared to lower the coolant level an inch or so. It was as if the hot air pushed the coolant out into the rubber hoses and engine. Would soft (original?) water hoses account for this?





I did some more checking and everyone appears to agree a loss of coolant indicates a failing water pump - even if there is no visible leak.

 

[Sprint 6]

Those will show a lower collant level with pressure on the system because that tank is a closed system. Relieve the pressure and the level rises because the coolant expands as it is exposed to atmospheric pressure.

Not to scare you, but a leak that you can't find on a 5.3 of that vintage is likely a porous head casting. Pull the valve covers and look for shiney clean aluminum around the three center head bolts. They don't leak enough into the oil to show in the oil.

 

[Steve@Advance]

Hopefully, when they replaced the tank, they didn't get all the air out. Once the air purged, the level dropped, now it is full and no more problems.

Common places to leak are the plastic adapters where the heater hoses go to the heater core. If they have not been replaced, they are cooked hard and ready to fail. Better to replace them now than on the side of the road!

Also look at the radiator, the front of the tank directly in front of where the upper hose connects. That is a heat concentration area, prone to crack. Look for discoloration from coolant running down. Stop leak will not fix it.

Look at the front of the heads, especially the left side. Known to leak externally. Hard to see, usually shows as a drip on the floor. Stop leak will "sometimes" fix it.

Same with the water pump. If it's leaking, look for coolant dripping from behind the pulley. Sometimes they will leak then stop, then leak again. If you do replace the pump, spend the extra for a GM pump, do it once.

 

[DoubleO7]

5.3L of that vintage also had issues with heads cracking.
Heads #706 prone to cracking.
#862 not so much.
Also prone to washing out the head gaskets and leaking coolant into push rod/rocker arm area.

The internal leak can be so small it will not make the oil milky.

Pull the oil fill cap and look under it for condensation. If there is any it will be your missing antifreeze.

 

[Bob]

(quoted from post at 17:23:14 04/25/18) Those will show a lower collant level with pressure on the system because that tank is a closed system. Relieve the pressure and the level rises because the coolant expands as it is exposed to atmospheric pressure.

Not to scare you, but a leak that you can't find on a 5.3 of that vintage is likely a porous head casting. Pull the valve covers and look for shiney clean aluminum around the three center head bolts. They don't leak enough into the oil to show in the oil.

"the coolant expands as it is exposed to atmospheric pressure"

You've re-written a basic law of physics here!

"Coolant" is a liquid and SHOULDN'T expand when relieved of pressure.

 

[1948CaseVAI]

(quoted from post at 18:23:14 04/25/18) Those will show a lower collant level with pressure on the system because that tank is a closed system. Relieve the pressure and the level rises because the coolant expands as it is exposed to atmospheric pressure.

If you could compress a liquid your hydraulics wouldn't be worth a darn!

 

[Hobo,NC]

Whut you call a expansion tank (reserve tank) is a Degas tank.

BACKGROUND OF THE INVENTION

In certain automobiles manufactured by various auto companies, the cooling system used for the engine is of the so called "closed" type wherein a plastic degas tank is provided that is physically separated from the radiator and is closed by a pressure cap of a type normally located on the radiator. The degas tank is operated under internal pressure of about 15 PSI gage and is connected to the engine and the radiator so that the coolant circulates through the degas tank. One purpose for the degas tank is to allow entrained air and gasses in the coolant to be separated from the coolant as the coolant flows through the degas tank.

Keep a check on it, it may not be a problem then it may be. I would not completely fill it worst case it will belch some coolant out. If it has the original hose I would order up new ones from GM if for nothing more than to replace all the plastic parts in the hoses THAT ARE GONNA BREAK!!!!... One overlooked problem could be the hose that goes from the top engine side tank to the radiator could be stopped up, are stopped up on the nipple at the tank are radiator. The hose is preformed 1/2" heater hose retailing for about $100 from GM... Its the only hose I make up from a roll of 1/2" heater hose I mark it and just swap it out every couple of years EZ as pie... The rest I pay the ransom fee ...

If it has a leak there is no reason it can not be found with a pressure test... The issue with those castech cylinder heads you do not have to remove a valve cover to confirm a issue just look at the oil filter it will tell the story... Dirty filter in the pix leaking castech heads at 3K miles...

 

[Grandpa's Fords]

As Steve@Advance stated

Hopefully, when they replaced the tank, they didn't get all the air out. Once the air purged, the level dropped, now it is full and no more problems.

My father's 2005 5.3 had new hoses installed at a local shop and after 10 mile drive light came on. Noticed the upper radiator hose was sucked in. I had recognized that problem from race car engines that were designed very similar. Took off hose after it cooled and filled it with water replaced it started the truck and kneaded the hose as it warmed and could feel flow. No more issue.
Most times they purge themselves but I believe the new but somewhat flattened preformed hose had enough restriction that it was limiting enough flow to purge.

 

[dhermesc]

I changed the oil in it last night - it appeared OK with almost 5K on it (black as coal though). I am sending a sample off to Blackstone Labs for analysis to make sure there is no coolant is getting in the oil.

 

[Hobo,NC]

Look at the base of the oil filter if its gummy that's not good it should be clean. If clean you don't have a problem...