94 Mazda MPV transmission

My buddy is having transmission issues in his 94 Mazda MPV. I'm going to quote what he posted on some forum. Anyone have any ideas? We think it is heat related.

Mike said: I still keep coming back to the heat issue. I can drive this van all over town (even in our 100+ days) under 60 mph and not in heavy stop and go traffic and it will never have a problem. Get in a lot of heavy stop and go or over 60 for 15-20 miles and it drops out of 4th/lock-up into 3rd gear. Even from a stop at that point it starts off in 3rd. I can manually select 1st and it works fine, bump the lever up and into 2nd and then into drive and it goes right into 3rd. Smooth as can be. Will not downshift if floored, but I can drop the lever down and I get 2nd or 1st no problem. If I let it cool for about 2 hrs and it is back to normal as long as I stay below 60 or keep it in light traffic. I have also noticed that when it starts acting up, the engine coolant temp starts creeping up as well. Otherwise it runs slightly below half gage. Since the transmission cooler is intergral with the radiator (which is less than a week old) I keep coming back to this being a heat related issue.

I don't know the answer, but I'm interested to hear possible solutions. My 92 mpv is used pretty much exclusively for towing my car and trailer so I would imagine I could soon run into similar problems.

maybe some of the passages are getting gunked up? perhaps a flush may be the ticket. also, if the rad replace happened recently, maybe one of the fittings going into the rad got kinked and is blocking up once pressure really builds in the lines?

my .02.

FWIW, auto transmissions have always been pandoras boxes filled with magic wizardry and voodoo juju from the great beyond that my puny mortal brain cannot comprehend, so I may be completely wrong in my entirety.

It's going into what we in the bidness refer to as 'limp mode', i.e. 'limp home'. That is generally a heat related issue as evidenced by the higher coolant temperatures (the hot tranny fluid is transferring its heat to the engine coolant).

Unfortunately, the additional heat is normally generated by slippage. There are two speed sensors, input and output and they have to agree within a certain percentage (this tells the computer how much the tranny is slipping) and if the right conditions are met of slip and heat the computer will stick it into 3rd (1:1 ratio) so you can 'limp home'. This means that most likely it will need a rebuild. If I were in your bud's shoes I would not drive it very much at all, continued operation in limp mode will cook the transmission fluid (if it hasn't already) and lead to much worse issues.

I would avoid a flush or filter change right now, if the fluid is burnt then changing the fluid can cause the transmission to not work at all. I have seen them driven in, change the fluid and then it won't even back off the lift.

We forgot to mention we did a filter change 3 weeks ago. The fluid was not burnt and there wasn't an abnormal about of gunk in there.

I'll pass on the info about limp-mode and slippage.

Thanks yall.

4cylndrfury wrote: FWIW, auto transmissions have always been pandoras boxes filled with magic wizardry and voodoo juju from the great beyond that my puny mortal brain cannot comprehend, s

My sentiments exactly, sir!

Then it's probably been caught early enough that a 'soft part' rebuild (seals, gaskets, clutch plates, bushings and bearings) will straighten it out. It might be worthwhile to run a 'line pressure' check first. If the line pressure is good it may be a valve body issue (unfortunately I doubt it going by the description of the problem), but in any event I'd not drive it any more than absolutely neccessary. Continued operation could roast drums etc and jack the cost of a rebuild way up.

If it turns out that the line pressure is low, then I'd look into a reman unit. Sometimes that's cheaper than a rebuild of the original unit. I'm not crazy about boneyard automatics; sometimes you get lucky sometimes you don't and that's a helluva lot of work. We had an insurance company insist on a boneyard tranny recently, they would only allow for R&R cost. The tranny really acted funky on installation, when we got permission to pull the pan we found that the filter was missing. That one was a nightmare.