Leaking coolant SOMEWHERE

2005 Tundra w/ 4.7. Recently I got this truck back from my son where the truck overheated. I've seen the other posts about the cheapy plastic radiators, and this one burst at the neck just below the cap. Since then, the radiator has been replaced twice, once the fix the original problem and the second due to over pressurization (cracked radiator again). It's gone a good while and maintained good coolant levels. However, my son reported it overheating again. Took it back to the same shop and had them thoroughly go over it. Did a 12-15 hour pressure check at 21 PSI, good. Checked for coolant in the oil, good. Did a dye test for any exhaust fumes in the coolant, also good. That all was about a month ago, today I had to add an entire gallon of coolant. The thermostat is working, and the fluid is moving via a new water pump (replaced when original radiator failed).

Today, however, I noticed as I refilled the coolant that the heater was only blowing cool air. I'm not detecting any coolant smell, either it being burned or being expelled by the heater core. I'm also not seeing any indications of a leak from the radiator, hoses, or the carpeting (via the heater core).

Can anyone suggest a course of action? The parts and labor are still under warranty, and I will be taking it back to the shop. But I don't like not knowing what's going on. Any help would be appreciated.

 

Try a new radiator cap.

It's prob not the cause but it's a cheap first step.

 

The heater blowing cold air is from an air pocket in the cooling system. The radiator needs to be the highest point in the cooling system for the air to burb out. If you have a slanted driveway park with the front up hill or put the vehicle on car ramps.

You covered most of the checks for leaks but I would also have a cylinder leak down check done. With the overheating and radiator problems I would really be concerned about a blown head gasket.

 

Radiator cap has been replaced. I'll burp it tomorrow. I'm also concerned about a head gasket, but wouldn't that have been covered with a dye test?

 

Clutch fan working properly?

 

Yes. Clutch fan is good.

 

Coolant can be leaking into the cylinders without exhaust getting into the coolant.
I would do a compression check.

 

Without any major wet spots, either on the ground or on the engine, it looks like the fluid is dispersing very discretely. I suspect a blown head gasket, warped head, or cracked coolant galley in the head and leaking into the combustion chamber or exhaust port area. A quick check would be to smell the exhaust at the rear of the truck while the engine is running. If sweet smell, the problem is as I thought. The overheating condition that repeats itself is often a sign of head work needing to be done.

Such has been my experience with cast iron heads, with the possibility that aluminum heads are more prone to this warping, but there is some doubt that I am reading this correctly and that the aluminum heads are more stable. But this we do know, that the loss of a pressurized system means the coolant temps will rise and that a sufficient loss of fluid may further acerbate the problem bringing much higher temperatures into play. My gut feeling is that the failed radiator which led to the first overheating episode, lost pressure and with the higher temp coolant causing the head to warp, a condition which may have become more severe as time and hours of operation takes an increasing toll on the warped head.

Also of note, such an internal head leak leaves no indications outside the engine unless the warping or blown gasket is sufficiently large, and even then it may evaporate quickly on the hot engine block. Unpressurized, it may stop leaking all together until the engine is again started. So goes theory...

 

Bump for update.