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My Chevy 2007 trailblazer LT [57,000 mi] transmission oil runs dry after 70 miles. Oil leakage seen at the breather. There are oil stains on the driveway but may be from another car. Bought car used, no warranty, 7,000 miles ago.

Symptoms: few days ago while parked, put in reverse with no gas applied. After 15 sec the car backed up. In drive from stand still hit 1000 RPM before car went forward. Hear some light metal grinding now and then. Various combinations of all the above. Anyway, adding oil solves problem temporarily. Had momentary slippage as I rolled car into mechanic's garage.

My mechanic [good guy but not a trans pro] put a tester on the car. Got a trans error. Don't know what number. Engine light is on. No other warning indicators.

What's happening?  

operating the transmission with the fluid level LOW.. where its slow to engage.. is a  BAD IDEA.. you will DAMAGE the transmission ..   not just the clutch friction surfaces.. but the front pump .. it was not designed to run completely dry...

fluid level is checked with the engine running in park on level ground..

if the transmission has an external leak... that has to be found and fixed...   the codes read and written down before any tear down... so the mechanic can see what the codes point to in the transmission to examine those circuits or devices while he is working..

again.. driving until the truck stops moving.. is going to completely destroy the transmission..

the transmission guys will probably add some to this thread.   sounds like its time for a mechanic who is familiar with transmissions.. or a transmission specialist..

you are not the first to have to rebuild their chevy truck transmission ..

if you had not operated it until it stopped working.. i would say it might be worth attempting to repair the leak..

it still might.. .............................  

You misunderstood a... limits of the computer. I haven't run it till it stopped. The mechanic added a few quarts yesterday when it was extremely low, and after getting home I was curious about the level - looked empty to me. A coincidence of timing.

So you're suggesting then same as the mechanic - there's leak number two somewhere?  

if its leaking... the LEAK has to be fixed....

the computer controls the Shifting of the transmission.. also receives signals from some of the sensors to schedule and calculate shifting ...


you also described it as making new scraping noises...

if it works when its full.. then there might be a chance...  i tend to read between lines..  so if you don't say it.. i may imagine the worst case..

the transmission guys always drop in early in the morning..   they can put this better than i can...

i have been at the computer since 5 am..  so i am kinda tired..   the monitor is kinda distorting..  but thats just because i am falling asleep.. not bad.. only 15 hours today..  

Good morning pmarc,

If you decide to work with a dealership on getting your transmission looked into, please be sure to let me know as I'm available to you throughout the process to assist as much as I can!

Sarah, GM Customer Service  

If the trans is in good working condition when filled up the source of ATF loss must be found.  If the fluid loss isn't external to the trans then there are two other possibilities.  One is that the trans cooler ( inside the radiator ) has sprung a leak and you would find ATF in the engine coolant, at the same time, this can cause engine coolant inside the trans.  Another possibility, and more common, is to have The trans fluid leave the trans and enter the transfer case- assuming this is a four wheel drive.  Pull the FILL plug on transfer case and if it is way overfilled then that is where it is going.  The transfer case would have to be pulled out and have the front seal replaced.  Drain and refill t-case with proper fluid.  It would be helpful to know what trans code(s) it had.  

OK. A trans expert looked into it. He found some device in the radiator went bad and coolant ended up in the trans. In fact he prefaced his findings by asking me first what hole I poured trans oil down - I did not. The mechanic did.. and in the right place. He says I need a new radiator and the trans is not worth rebuilding because stuff got inside and made it unpredictable to keep using it, and also no telling how much extra trans work it might take. Which is probably a lot. Says he'll get a trans somewhere and install it. $3,500 total.

I'm getting a 2nd appraisal tomorrow, but what are all your responses on this now? He topped off the trans fluid. The engine now sounds like a loud whirring sound. Like a truck with a hell of a lot of torque. Or like sucking air.

I'll get a 2nd opinion tomorrow. If it's the same I'll go back to the first guy who was referred to me by a god mechanic.

How does anyone respond to all of this? Thanx.  

Engine coolant in trans means that it does need a rebuild or replacement but does not necessarily mean that it can't be rebuilt.  That can only be determined by removing, disassembling, and inspecting parts to see if a rebuild cost exceeds a remanufactured unit.  I have rebuilt many units with coolant inside.  Excellent choice to get a second opinion from a reputable transmission shop.  It would be a must to replace radiator and flush cooling system.  

" removing, disassembling, and inspecting parts to see if a rebuild cost exceeds a re-manufactured unit "

You're saying someone will want to do this inspection at no cost?  

I would get estimates on used vs rebuilt vs remanufactured and decide what you can afford.  The trans has to come out either way you go.  At that point, they could disassemble trans. and give you an exact estimate to rebuild.  GM remans are good units but usually more expensive than a rebuild.  A used unit is usually the cheapest way out but you have no idea what you're getting.  You might pay to have it installed only to find out it has more problems than what was in there.  That wouldn't be the installer's fault since you're only paying to have a used unit installed not have it disassembled, cleaned, and inspected.  Just like any trans a 4L60E has several updates while rebuilding it.  How good the rebuild is comes down to the trans tech that does it.  

Since you only have 57,000 miles most likely your trans will not need a lot of hard parts. The coolant mostly just swells up seals,o-rings and ruins electronic parts. That trans should be very rebuildable. I'm not sure how much those radiators cost but $3500 for that job is a little on the high side.  

The 57,000 conclusion is sound. Used def out. By the way, no one at edmunds.com replied on this subject..? Thanx, I can handle it from here. Good luck to all.