Overheating and no heat

[Scharper]

2003 Tahoe 4x4 5.3

Saturday I towed my boat 1 hour each way, no problems. Sunday, I drive it 10 minutes and its overheating.

Conditions:
-No heat in the climate control system (was working prior to overheating)
-Been getting a random "low coolant level" message on the dash for several weeks even though there is enough coolant in the reservoir.
-No coolant leaks.
-Looks like the radiator fan is spinning, though not fast and loud like I would expect. But it overheats while at speed as well when I would think it would be getting enough air-flow naturally.

Other, probably unrelated, conditions:
-There was a collision on the front passenger side some time before I bought it a couple months ago.
-Oil leak from the valve cover gasket.
-CEL for evap system.
-AC doesn't work (never has since I owned it)

I'm planning to flush the coolant. Should I keep using DEX or go to something else?

From what I've read, given my conditions its either a blockage in the coolant lines or the thermostat. Anything else? Any way to tell for sure?

 

[Larryjb]

I would check the following:

1) check that the system is purged of air.
2) do a pressure check (engine cold).
some leaks are slow enough that the leaking coolant evaporates before you can see it. A warm engine would push coolant out the leak area, then pull air in the same spot as the engine cools. If this does happen, you won't see the coolant level drop in the reservoir, but you will still go low on coolant.

The leak could be external, in which case you should be able to see it during the pressure test. If the leak is internal (into the intake manifold or cylinder) you won't see it, but your pressure will drop. You might have to leave the pressure tester connected overnight. Keep in mind that as the night cools, the pressure will drop slightly even if there are no leaks. I've found several leaks this way, and I couldn't see coolant leaking otherwise.

Larry

 

[Larryjb]

Dexcool was an issue on some cars in the 90's. Air would enter the system, often through the rad cap on the radiator so the driver didn't see the level drop lair war pulled through the faulty cap, not from the reservoir). Air + the organic buffers in Dexcool made the coolant go acidic. Acidic coolant + heat eroded the nylon intake manifold gaskets. I have not heard of this situation occurring in the GM trucks, but t guess it is possible. lf I were to switch, I would competely flush every bit of Dexcool out (hard to do) then switch to Zerex G05. However, I'm not very concerned with the truck engine and will likely keep the Dexcool. I did change my le Sabres.

Larry

 

[Larryjb]

I just did a quick search and did find some intake manifold gasket failures, so perhaps Dexcool is an issue in the GM truck engines. However, it doesn't seem nearly as bad as it was in GM's 3.8L engines where some engines hydrolocked!

Perhaps, for peace of mine, switch to Zerex G05. Some of the green coolant contains the same organic buffers found in Dexcool, so I'm not convinced that switching to green is the best solution. If you do flush, you need to flush ALL the Dexcool out. I would drain the coolant, use my wet shop vac on the lower rad hose, then fill with distilled water. Then I'd run the engine until it began to flow through the thermostat, stop, cool, drain again. I did this until I could see not trace of Dexcool orange, but this took about 10-15 flushes!

Larry

 

[Scharper]

Thanks for the quick replies! I don't have a pressure tester. Is there another alternative?

 

[Larryjb]

I think this is the only way to reliably find leaks. They're not too expensive, and you can probably borrow one from Orielies. I've use my kit many times, and I'm just a DIY.

Larry

 

[Scharper]

Ok, I got a pressure tester loaner from an auto parts store. I pumped up to 10psi and it comes down a couple psi in an hour. I don't see any leaks anywhere though. The oil looks perfectly clean, no bubbles so I don't think its a head gasket. How do I check that the system is purged of air?

On a side note, when it was overheating, the upper radiator hose was burning hot, so I'm thinking the thermostat is probably good if it was allowing the hot coolant to flow to the radiator, correct?

 

[ISU-152]

Might I suggest removing the thermostat and running it open loop for a bit? If the thermo is stuck closed then obviously no coolant will be flowing. You said you had the low coolant light...so in open loop the coolant overflow should drop right away and you've got your answer.

Are you parked on a decline a lot? As in nose down? You also have no heat which might mean an air lock in the heater core.

 

[retiredsparky]

A cracked head(s) can allow coolant to leak into the valve cover area. This type of leak happens more often in heads with a #706 embossed on the upper face of the head in the lower right corner. Google Castech heads. This type of leak can be so slow that the coolant mostly evaporates in the top of the head. Some will leak into the oil, but so little that there may be no "gravy".

Another common leak area is the tees that send coolant to the rear heater coil, if you have that option. The tees are located above the rear part of the engine at the firewall. The tees have o-rings which over time dry out and shrink. These tees should both be replaced at 100K miles. They leak very little, so it helps to pour some fluorescent dye (auto parts stores) into the coolant. Run the engine. Use the included black light flashlight to look for the dye leaking out. There are a lot of leaking tees out there, but their location makes it less likely to see a leak.

 

[Scharper]

Another common leak area is the tees that send coolant to the rear heater coil, if you have that option. The tees are located above the rear part of the engine at the firewall. The tees have o-rings which over time dry out and shrink. These tees should both be replaced at 100K miles. They leak very little, so it helps to pour some fluorescent dye (auto parts stores) into the coolant. Run the engine. Use the included black light flashlight to look for the dye leaking out. There are a lot of leaking tees out there, but their location makes it less likely to see a leak.

I believe that is the problem. I just re-pressure tested and noticed a pretty good leak (much worse when touched) from a tee-connector just behind the trans fluid dipstick. Would it make sense for that to be my only problem causing the overheating? Truck has 220k miles.