5VZ-FE slow coolant loss

Hi all,

I’m working on a 2003 Tundra with the 3.4l 5VZ-FE and manual trans. I’m experiencing a slow loss of coolant that I first noticed about 6 months ago. I have since monitored the coolant level closely, but have had no luck tracing the leak. The most I’ll lose is about 2 inches from the reservoir over about 100 miles. I found a small leak from the water pump. I then replaced the water pump including new factory gasket and thermostat/gasket with jiggle at 6 o’clock. Still losing coolant. ECT is no greater than 181 degrees while driving. I have not experienced any performance issues, no overheating, no coolant on floorboard, and no signs of oil/coolant mixing. I’ve scanned relevant threads and I’m thinking a small leak at the coolant bypass tube inside the intake manifold or maybe a small leak in the radiator. Only leaks while running. About ready to try a pressure test, but would appreciate ideas/suggestions.

Thanks

 

You might be losing it through the exhaust. Not large enough to produce a steam trail but enough to notice.

 

probably a head gasket leaking. most likely into the combustion chamber, so it gets burned and there is no sign of leakage. there are several tests to confirm.

 

I can't keep my overflow reservoir full, either. People told me I have a head gasket leak, but I refuse to believe it! I just run the reservoir empty and no problems running or overheating.

 

Yep, I second this. The 1st gen I had intially had a two cylinders with small cracks in the head between the coolant flow areas and the exhaust valves. Coolant would leak into the exhaust and get burned off - very slowly like you describe. My head gasket was fine, but the truck was overheated by the previous owner and the heads were slight warped as well.

Either keep and eye on the coolant and keep refilling it, or do a pressure test and start dumping money into a fix (rebuild).

 

The thing is, the radiator stays full of coolant. Only the reservoir drains off. No pink stains anywhere indicating a leak in the reservoir. Maybe it's evaporating??

https://haynes.com/en-us/tips-tutorials/7-different-ways-head-gasket-can-fail

I don't believe it. I will do a leakdown test next weekend though. My compression test results were terribly low, though.

 

Think about the point of the reservoir. It's job is to supply coolant when the radiator is low, and accept it back under sufficient pressure.
If you're losing it from the reservoir, you're losing it. If you don't see it coming out of any external coolant tubes, then there's only one other place: internally.

 

I can't dispute the logic of that, but I also can't explain how my radiator stays full, years of driving with an empty reservoir, but as soon as I top off the reservoir it quickly vanishes. Conundrum I gave up on.

 

I mean, the reservoir is only supposed to be filled halfway, for the record

 

I'll bet the Radiator Cap gasket is bad.
Or the neck of the radiator isn't seating tight to cap.
That's why no visible sign of leak.

 

You'd see white trails

 

The radiators are notorious for cracking and leaking with age.. Check that thing real hard for leaks

 

it's just a matter of time before it gets worse and you will have an overheating issue, which could warp your heads, and even strand you.

 

the coolant has to go somewhere, simple physics. either it is leaking into your cylinders or the radiator or some other part of the cooling system.

 

Thank you all for the input.

To clarify... I have already replaced the rad cap and the coolant loss is not limited to my reservoir.

I think I’ll start with a radiator pressure test before conceding to larger problems.

 

Sorry I hijacked the post with my own issue. Glad you chimed in to get it back on track.

 

Check out these good resources for pinpointing a coolant leak:

https://www.youtube.com/watch?v=rDuGeQnMOzk

https://www.youtube.com/watch?v=7RDarciXfwg

 

there are 2 coolant lines that go from the back of the intake manifold to the Idle control valve. They will seep and the coolant will drop onto the intake and "disappear".

 

Update:

Borrowed a radiator pressure test kit. Pumped up to 13psi. Gauge dropped to 12psi within 15 minutes then stayed there...relieved pressure and disconnected after an hour (still at 12psi). I’ve looked everywhere possible without starting to take things apart. Still no luck finding a leak. I guess a dye and uv light might be next. Any thoughts about the dye/uv and next steps?

 

Years ago, I kept losing coolant just like you have pointed out. I could not find leaks and never.had anything on the ground. I son's remember if it was late fall or early spring I was parked in my driveway, which has a good slope to it, with the Taco idling. I was coming back out of my garage and finally seen something dripping under the truck. The drip was coming from the back of the motor.

Anyway, the coolant was leaking into the void under the I take manifold. Can't remember the space of the leak, but the combination of it finally leaking enough to fill that void and the slope of my driveway caused it to run out at.the back of.the I take and down.the back of.the motor.

I was luck.that my truck was still under the extended warranty, as the dealer tore down the motor to clean everything up.