Is this really the problem?

My dad’s 1996 Toyota Tocoma truck was passed on to me after his death. We have had sever repairs. It has 118,000 miles on it. Most recently, the engine light came on (last week) and we found out that it was the catalaytic (spelling) converter. Our mechanic replaced it. When we got it back home, the very next day, the truck was still slow in changing from first gear. After it warmed up it seemed to be fine. But we took it back to the same mechanic and he looked at the transmission fluid and found that it was realy black and dirty and oily. He thinks someone somehow put oil in the transmission fluid container instead of transmission fluid. He has taken off the pan and cleaned it out, changed the filter inside this pan, and put an additive and clean transmission fluid in it. He said it was suppose to be pink in color and clean. When he was in the pan, he said it was really dirty and black. Does this sound right? And how would black dirty oil get into the transmission? Do you think this has damaged the transmission? We don’t know how this could have gotten inside the transmission. It seems to be running ok but we just got it back 2 hours ago. What do you think the problem is. It was going really slow during the cold mornings and when it warmed up it seemed to be running ok. Now it seems ok, but a little funny running, not the same as it was. Can you offer any suggestions as to what the problem is and how the transmission got so dirty. Also I don’t have any records of the service my dad on the truck when he had it. I guess he only did the oil change, etc, not the regular service recommended by the dealer. My mechanic told me that the catalaytic converter should have been changed out at 50,000.

Thanks for your help.

Jennie Bingol

Jennie, first question: Has the truck been used for towing a boat or trailer ?

I question your mechanic: “catalytic converter should have been changed out at 50,000.” Huh? That makes no sense.

As to transmission fluid - when was it last changed? While it should be pink/red, old fluid can look as you describe.

‘Really dirty and black’ most likely means the transmission has never been serviced. Cleaning it out and adding an additive may extend it’s life, but it is hard to say what damage may have been done.

Also, the catalytic converter does not need regular replacement. I’ve never had to replace the cats on any of my cars or trucks. I kept all of them in proper tune, done all the recommended maintenance, and have addressed any problems promptly. The catalytic converter is designed to out last the rest of the car if this is done. An out-of-tune engine, or continuing to drive with a known problem are sure ways to shorten a catalytic converter’s life. To give you an idea of the vehicles I’m talking about, an '82 Honda Prelude, '88 Ford LTD, '00 Ford Explorer, '90 Toyota Pick-up, '88 Toyota Supra, '92 Toyota Celica, and a '90 Mazda Protege, all of them with 200,000 miles or more.

Your story sounds extremely familiar. When people get older, looking after a car often gets put on the back burner or gets forgotten altogether.

It’s quite possible your dad accidentally put engine oil in the transmission. They come in the same shape 1 quart bottle. It’s also entirely possible he did not change the transmission fluid and filter.

Your mechanic was helpful in trying to find the cause, and now that the fluid and filter is changed, chances are your transmision will be OK.

If this was my truck, I would also do the following:

1)Flush the cooling system and replace any weak hoses. Your mechanic will know what to do. Budget about $85-$100 for this.

2)Have the brakes checked.

3)Check the battery to make sure it will make it through the winter.

  1. IF this engine has a timing belt, replace it and the water pump; this should be done at the same time as flushing the cooling system. If the engine has a timing CHAIN, no need to replace since they last the life of the engine.

No it has not.

This is what he told us, we don’t know what is right from wrong.

We have not changed the transmission fluid in the two years we have had the truck. Do you think it just got old and dirty?

This same mechanic has flushed the cooling system, also replaced the brakes and checked the battery. I don’t know if the engine has a timing belt. I would have to ask.

I would not trust a mechanic who said that catalytic converters need to be changed out at 50k miles. He is either very misinformed or else is a crook. Did he show you the fluid? Did you see him take it from the transmission or is he possibly showing you old engine oil to make easy work for himself?

You need a second opinion at another mechanic.

We have not changed the transmission fluid in the two years we have it.

When the engine light came on, it was on a Saturday, so we went to an Auto Zone and they came out and put the diagnostic tester on it. It said it was the exhaust system. So on Monday, we took it to the mechanic and he put his tester on it and read the code to be the catalytic converter. So he replaced it. then the next day it still was not normal. Seemed to having trouble shifting from first to second. It is an automatic. So we took it back to the same mechanic and he looked at the transmission fluid and fouund it to be black and dirty, thinking someone put oil in the transmission instead of transmission fluid. He was not sure, but he kept it overnight so that he could check it out when it was cold in the morning. He then cleaned out the pan? on the transmissin and changed the filter, saying that it was really dirty and black. That the filter was not letting any fluid get through. He put an additive in and also put in new fluid. Ask us to drive it around a few days and see if this helps, if not come back.

we don’t know what is right and what is wrong, this is why I am asking to see if anyone can tell us if this seems normal. I had a 90 Toyota Celica with over 200,000 on it and never had to change the catalytic converter either. So he may be wrong, but the code said it was. I don’t know. He may be ripping us off.

It certainly could be the fluid was just old and dirty. Have him show you how to check it. You may need to change it again shortly if some of the old fluid was left behind, it’s hard to get it all out.

And just ask him why he said that about the cat. converter. He may have a good reason.

I’m not jumping to the conclusion that he’s a crook or the truck didn’t need a new cat. A car or truck that has not been maintained correctly can compromise a catalytic converter. I’m just disagreeing with the notion that the cat needs replacement every 50,000 miles. I know for a fact this is not correct.

Thank you, I am glad you told me about the 50,000 miles. What is maintained correctly? We have regular oil changes, brakes checked, tires rotated, balanced, etc. But we do not have regular shecduled maintenance that the dealership recommends. We feel they charge way too high prices. We take in the car or truck if we feel something is wrong or sounds wrong or the light comes on.

IF the engine is a V6 (3.4L), the TIMING BELT will require changing every 90,000 or 100,000 miles. Change the water pump at the same time. It’s driven by the timing belt. If the engine is a four cylinder, it has a timing chain. Don’t worry about it.
If the engine still isn’t in tune, it can knock the catalytic converter out, again. The engine should be in such tune that it runs very smoothly under all conditions.

Maintained correctly is doing at least the maintenance recommended/required in the owner’s manual or maintenance schedule from the manufacturer.

Transmission fluid is oil and it will get black and dirty. I don’t care for additives in transmissions but most are probably harmless, just a waste of money.

Toyota transmissions require a special grade of transmission fluid, if your mechanic used Dexron III, that can cause shifting problems.

When the transmission fluid is changed, only about half of it is drained out and replaced. If your transmission was allowed to go 118k miles without service, you should go back and have it changed again after 100 miles or so. You may even need to do a third change in another 2 or 300 miles to get it clean enough.

As for the catalytic converter, if you had a P0420 code, the cat may not have been the problem, it could have been an O2 sensor. The code is catalytic converter efficiency below threshold and it is comparing the outputs of the front and rear sensor. This is a difficult code to troubleshoot.

He probably meant the transmission fluid should be changed at 50,000 miles. Maybe then or at some other mileage.