Cooling System Diagnosis

Over the weekend I attempted to drain, flush, and refill the cooling system—first coolant change of the vehicle. I didn’t bother with the engine drain plugs I only drained from the radiator. I started the truck with the radiator valve loosened to attempt to drain the coolant inside the block and wherever else it would be. I managed to drain about 7.5L. The system holds around 9L, so couldn’t catch it all. I flushed with distilled water then drained, flushed etc. I refilled with super long life coolant and am now trying to burp the system. How exactly should this be done; I am finding conflicting methods. Are we supposed to have the fan set to hi, lo, or off while running the heater? Are we supposed to squeeze the upper and lower radiator hoses? Should my lower radiator hose be cold? I used a spill free funnel and topped the coolant off. Started the truck and let it get onto operating temp while running the fan on high with max heat setting. I squeeze the upper and lower radiator hoses but every time I squeeze it’s the same bubble popping up; doesn’t seem to get any better. Also, my lower radiator hose is cold. I ran the truck for half an hour and this is where I am at now. Need a consistent method to follow and whether the constant bubble along with the cool lower radiator hoses is a potential problem. I know this is a long post, sorry about that. Thanks in advance

 

The fan does nothing but blow air. Just shut it off.
Set the temp control to full hot.
Park the truck facing uphill if possible and run the engine with the rad cap off, add fluid as necessary.

 

Heater on high will ensure coolant is circulating through the heater core. Fill radiator up best you can getting as much air out as you can, fill or overfill the reservoir. A couple warm it up, cool down cycles should get any remaining air out. Then if you're still uncertain, once fully cooled down, like overnight, pop the radiator cap. You can stick your spill free funnel on and squeeze the hoses, no air should come out. Then you might need to add some more to the reservoir. If it's overfilled, it's not the end of the world, it'll spit out the excess, something to keep in mind if you have pets.

I've seen some very poorly designed systems that are very difficult to get the air out. Caps mounted low so the radiator can't be fully filled. Hoses that arc up higher than the cap. Pira.

 

So the air in the system gets worked out after a few warm up and cool down cycles? Over the next few days I will check it cold and add to reservoir. When the truck is cold it should be at low, but when I went for a drive today and checked the reservoir warm it was only slightly above the low mark. Should it be at the full mark once engine has hit operating temp? If so I will add some more when engine cools down to get it to full mark. what about the fact that my lower radiator hose is cold when my upper is hot? To me it makes sense that it’s cold since that’s the radiator job—to act as a heat exchanger and cool down the hot coolant coming from the engine, but when I look it up online some people are saying it’s a sign your thermostat hasn’t opened up?
I guess this whole process is easier if I understand the mechanics, which is what I am trying to do

 

Air should purge out as long as the reservoir isn't empty or very low. I suspect your warm up drive isn't enough to open the thermostat. Both hoses should feel hot to the touch. Thermostats have a tiny hole, imagine a hole with a rivet that's too small so it jiggles around allowing a snall amount of hot coolant to bypass even though the thermostat hasn't opened yet. That would explain one hot & 1 cold hose.

I'd go for a freeway drive, leave the heater on hot/low fan. Fan on high will pull heat out of the system so the thermostat might not open. Drive long and hard enough to get that thermostat opened. Watch the temp gauge, if it buries into hot, thermostat is no good. If it stays fairly steady no matter how hard you floor it, thermostat is doing it's job. Then top off reservoir to the hot line before it cools down. If you fill to the upper hot line when it's cold, it'll just come squirting out. One more top off the reservoir hot in a week or two you should be good.

Remember the radiator cap condition? The rubber part should not be cracked or swollen making it difficult to put on.

What combination do you have? 6 or 4cyl, manual or auto?

 

Here's how I do it on a full flush like you did.

Assuming empty.

I remove the upper heater hose, fill with hose off, plugging one end.
I fill until its flowing out the heater core and plug off temporarily.
I then fill and ensure the fill funnel is the highest point.
Run until I have full heat on both heatercore lines, usually 2500rpm with heat on max recirc.
If I dont have heat and my temps are rising, I shut it off with revs, let it burp. Start it again.
If I still dont have heat and my temps are rising past operating, I pull off the heater line while its running, this is an old method that still works for me. The air traps in high points, and the heater core is higher than the cylinder head.

 

Just watch the reservoir level over the next few days and top off as needed. Also check under the radiator cap when the engine is cold (sitting overnight) and add there too if needed

 

I've done similar. After draining, disconnect both radiator hoses, garden hose in the upper hose, engine running, bottom hose spewing all the rust crap out, try to match the garden hose pressure to match what the engine will consume so it isn't spewing out the top. For when some previous owner only ever added water. Then I like to flush with distilled a couple times to get the garden hose water out, then fill with coolant and distilled water.

 

You should have opened the block drains, there's quite a bit that stays in there you'd be surprised. As for refilling, the FSM lays it out pretty well. Leave fan on low, place heat on high, massage those hoses, take for a drive and repeat. I always park on a slight incline as well to help dispel any entrained gas. Sometimes it takes a few drives around town for all the air to bleed out.

 

A lot of responses, thanks everyone. I am taking it all in.

1. I have the 4.0L V6
2. My upper rad hose was hot, very hot, but my lower was cold. If hot coolant is entering the upper hose is has to be going down the radiator so having the lower hose cold would have to mean it’s effectively cooling down?
3. When I ran the burping process I had the heat on and the engine was blowing hot air, so wouldn’t that mean the engine has hit operating temp? Wouldn’t that also mean the thermostat has already opened up? And since my upper rad hose was hot that means the thermostat was open right?

 

Hot air doesn't mean air is free, but it is a good indicator.

You want to feel heat in both upper and lower rad hoses. Same with the heater core lines near the brake booster. You want them both to be hot. Sometimes we block the radiator as the fan will cool the radiator with time.

Honestly if its already sat and hasn't overheated its likely fine.

 

I’m in agreement with bishop, you’re probably ok.

Is the ambient air very cold where you live? If yes, your thermostat might not open at all until it warms up outside. That would also explain the lower hose being cold.

By now, I’m certain you’ve purged the air out of the heater core. During burping did you have it on max heat, fan low? If you had the fan on high you’re defeating trying to get the coolant hot to open the thermostat. Did you top off the reservoir to the upper hot line while the engine was still warmed up? If after sitting overnight, there’s anything in the reservoir then you’ve probably burped all the air out, don’t take the cap off now or you’ll put air back in. Fill the reservoir to the upper hot line with the engine warmed up, check the reservoir in a week & top it off if needed hot one more time, good.

One winter I turned turned my heater on for the first time in months. Suddenly my radiator was very low. Filled it, next day the top plastic end tank cracked. I knew my thermostat was stuck open because it would take forever for the engine to warm up. So now I always run the heater, even for a little bit when it’s summer hot time. Honestly don’t know if any problem had to do with another or my heater exercise helps at all.

 

Yeah it didn’t overheat. What do you mean by hot air doesn’t mean air is free?
Should my radiator/cooling fan come on as soon as the engine is on or should it only come on when the vehicle hits operating temp?
I live in a cold area and it was very close to freezing when I done this job. I understand what you are saying about the thermostat may not even open in a cold climate but I was under the impression that the thermostat opened up since my upper rad hose was hot. If my thermostat stayed closed the coolant would just be circulating the engine block/heater core and not even be sent to the rad to cool off? But since my upper rad hose was hot I thought the thermostat had opened. Either way my upper rad hose was very hot and my lower was cold. Is there anywhere else for the coolant to go between the upper and lower rad hoses? If not, still kinda stumped as to how the upper could be hot and the lower cold.
Yeah my system is probably ok I will definitely top the levels up with coolant as you have all mentioned. My interest now is purely academic so I can understand the cooling system as much as possible. First step in solving a problem is understanding the problem

 

the upper radiator hose is the outlet so it will be hot almost immediately. It will not flow through the radiator until the thermostat opens up, hence why the lower coolant pipe would still be cold. Here's the water circuit

 

Electric radiator fans mostly are temperature controlled. So maybe the thermostat opens at 185, then the fan maybe turns on at 200.

It’s all a learning journey

 

thermostat should start to open at 176 to 183°F and should be fully open at 203 deg F. The "reset" on the thermostat should fully close it at 171 to prevent excessive cycling. The fan is not electric in the 2nd gens, it uses a fluid coupling.

 

Uh oh, a bad fan clutch? Or aftermarket electric fan?

 

If your fan has a belt attached, which it should, any time the engine is running the fan needs to be spinning. If it isn't your fan clutch or fluid coupling is trash & needs replacing. If you're fan doesn't have a belt attached, instead has wires sticking out of it, it's an electric fan. If it's a quality electric fan, good. If it's a cheap one ALWAYS watch your temperature gauge. Worst case, on a hot day, stuck crawling in a traffic jam, very little air is flowing across the radiator, a cheap electric fan fails, you overheat.

 

It’s bolted to the water pump pulley. If the water pump pulley isn’t spinning it will be overheating in a very short time. If fan isn’t spinning, clutch fluid is likely low.

 

I doubt it’s an electric fan so it just be operated by the drive belt, that makes the most sense. There is nothing aftermarket on my truck as of right now. I am finding it hard to follow along with that water circuit diagram, but it’s stuff like that want to see. What’s the deal with FSMs? Are we able to buy them or is not for public sale?