2003 buick la sabre cooling/trans problem

my car recently started running overtemp not much, but enough to bother me. I flushed the system with no change. after about a week with continued symptoms, my trans started shifting hard between 1st to 2nd and 2nd to 3rd, and running rough in general, sputtering lightly in high gear. I assumed it was running over temp with the rest of the car, so I replaced the radiator and the radiator cap, yet still am having the same problem. Is it still related to the cooling system? if I replace the water pump will i solve my problems, or is it really a hidden trans problem? I’m fairly certain the trans has never been serviced, and I’m reluctant to do so given the high milage, 174,000. The fluid is full, but its very thin, and no longer red, its sort of a pale yellow.

fans work fine, and thermostat is also new.

The old radiator could have had a ruptured transmission cooler, which is inside the radiator, which introduced engine coolant into the transmission. If this has happened, the transmission cannot be saved by changing the fluid. The transmission MUST be removed, completely disassembled, vatted to get every bit of coolant out, and rebuilt. Engine coolant will very quickly destroy the friction material in the transmission i,e. clutches and bands. The friction material will start to fall off of its steel backing plates in chunks. Basically, your transmission is suffering a slow but sure death. If the fluid has never been changed in this transmission in its 174k life, then it has been SEVERLY neglected. You should always change your transmission fluid and filter every 25-30k miles regardless of what the owners manual says.

Heres what I would do. Take it to a local transmission shop and have them determine whether there is any engine coolant mixed in with the fluid and see what they find, you could be lucky and it just be a sensor or electronic item failing. If thats all it is, throw in a trans service while you are there.


What year is it? There must be a check engine light involved.

If you got 174K out of that transmission without ever servicing it, I’d call it a minor miracle. Have you actually looked at the transmission fluid? Is it all brown & dirty looking? Maybe very dark and burned smelling? If you had really old fluid that then became overheated from running too hot that wouldn’t be doing the transmission any good either.

the trans fluid was very brown and dirty when I pulled the lines off the radiator, but the dip stick isn’t. its like i said, pale yellow. is that an indication that coolant mixed with the trans fluid? there isn’t a check engine light on. didn’t come on once. also don’t i take the chance of blowing the trans up if I change the fluid at this point. I’ve had this happen before. also which sensor are you referring to.

also fluid is yellow but its clear. not milky at all.

I have never seen trans fluid contaminated with coolant before so I can’t tell you if that’s it. I can tell you that yellow to clear is absolutely the wrong result. It should be red - except yours is so old that you’d find something more like brown. Either way that fluid is shot - and your transmission probably is too. What did the coolant look like when you drained it after initially having the hot running? Is the transmission over full?

If you service a transmission - regardless of the miles - and it fails soon afterward its just because it was coming anyway. Unless something boneheaded is done such as use of the wrong fluid, over/under filling or maybe failing to install the filter properly.

When transman referred to “a sensor” or “electronic item” it wasn’t a reference to anything specific. There are multiple sensors & electronic items involved in running the transmission. Of course, you still haven’t said what year it is which really cuts down on anyone’s ability to elaborate.

could it be just a bad water pump not fully cooling the car and trans? I’m still running hot at an idle with the heat off. not over heating just above normal temp.

its an 03. its in my heading i thought

My bad on the year - I sometimes do read past that.

How long have you owned this car? I ask because I have a '00 olds van which uses a lot of the same stuff. My temp gauge in unbuffered meaning that, unlike many gauges, it actually rises & falls with engine temp. While driving it sits about 1/3 of the way up the gauge (a little variation for ambient temps). If you sit at idle it will climb to about 2/3 and then the fan kicks on & it comes back down to where it was. It will do that all day long if I leave it sit at idle. If yours just continues to climb then you need to recheck the cooling fans and the coolant temp sensor.

As transman said earlier, you’re just going to have to take it to a trans shop for the transmission issue. If the car isn’t overheating then replacing your water pump probably won’t do a thing - for the transmission or otherwise.

My guess on your transmission is that it is, in fact, at the end of its life. The computer is picking up long shift times (too much slip) and is maxing out the line pressures = hard shift. The “sputtering” is probably a slipping 4th or a slipping torque converter clutch.

The most influential “sensors” for shift quality will be the throttle position sensor (TPS) and mass airflow (MAF) sensors.

and if those senors were bad there’d be a code. the temp gauge never fluctuated before so i thought there was a chance that it might have something to do with the trans problem as both problems arose at the same time. I bought some lucas trans additive, it saved a previous transmission for me in the past, so here’s hoping. just out of curiosity, did i just waste 100 dollars on a radiator?

When did you replace the thermostat? Was it before or after the engine started running hot?

The sensors can have problems without throwing any codes. They can easily be “wrong” but not out of spec.

These GMs can have codes that don’t turn on the check engine light. You probably have error codes relating to transmission functions.

These transmissions do have problems with pressure control solenoids & there is reason to believe that heat is one thing that can send them screwy. But by the time you’re into getting the side cover off to replace it, you might as well the pull the whole thing out & do everything.

Based on your description of the trans fluid you got out when you pulled the lines of the radiator, it sounds to me like the coolant and the trans fluid have mixed thoroughly. That glopy brown stuff is what you get when you do that.

All symptoms taken together, I have no doubt whatsoever that Transman is correct. It fits the description, the engine cooling problems, and the tranny problems. Follow Transman’s advice.

before keith.

way before though like last summer

yes but why don’t i see that stuff on the dipstick?

It doesn’t matter why you didn;t see it on the dipstick. You’ve seen it in the tranny cooling lines. That’s definitive. It’s in the tranny too.

You need to accept the truth. You have all the signs that the fluids have mixed and you now have a choice:
follow Transman’s advice or drive it until it dies, which will be any time now.


If you really want to kill the transmission faster and P/O your rebuilder then add the Lucas. Do what I said on your trans then post back with the results. There is nothing else YOU can do with it, and by all means, go get your money back on that Lucas.


I talked to my mechanic, and decided to try a flush and new filter first since the trans seems to not be too contaminated. here’s hoping. I’ll let you know how it went.