Van reluctant to shift into 4th

[purplegreendave]

At the beginning of every journey, my van doesn't want to shift into 4th for the first 40 - 60 minutes of the journey. Once it has done so, the shift is smooth as butter and for the rest of the journey it will shift in and out without any trouble. If I kill the engine, even for a few minutes, the problem reappears.

I'm hoping it's just a sensor somewhere, the tranny fluid looks to be at a good level (maybe even a bit on the high side) and not discoloured. It's a pretty irritating problem though, travelling 45 minutes to town in 3rd for it to shift into 4th as I arrive isn't good for my wallet, and can't be good for the car as a whole.

[timsrv]

There's a temp sensor on the engine that prevents OD operation until coolant temp is over 140 deg F. One possible cause for your problem is long engine warm-up due to an engine thermostat that is stuck open. Another possible cause is the OD temp switch is slow to open. If your temp gauge takes a long time to get to normal, then replace the engine t-stat (use an OEM Toyota one). If engine temp isn't an issue, then disconnect the OD temp switch to test.

I'm not exactly sure why Toyota doesn't want OD to happen when cold........perhaps they did that just so the van would warm up faster??? Regardless, I consider that feature worthless and I've run one of my vans for years with that switch disconnected. Here's a thread that explains the OD circuit more and shows a picture of that switch & it's location: http://www.toyotavantech.com/forum/showthread.php?556-Sensors-to-overdrive

[purplegreendave]

If your temp gauge takes a long time to get to normal, then replace the engine t-stat (use an OEM Toyota one).
What's a long time? It seems to climb fairly reasonably for 20 minutes or so and then a lot more slowly for the last few degrees (another 10 - 15 minutes).

It is a little happier now that the weather is picking up which is reassuring (I think?) - at least it's probably a circuit problem and not a transmission replacement!
I lifted the passenger seat and it looks as though someone already pulled that sensor - is there any way of testing the thermostat before buying a new one?

[timsrv]

Van should get up to normal running temp (about 1/4 - 1/2 of the way on the temp gauge) in under 10 minutes of driving. Once it's reached it's normal spot on the gauge, it should stay there and not creep up (may be exceptions for severe driving conditions, but return to normal spot when driving conditions return to normal).

Other than a quick visual inspection I consider it a waste of time to test the thermostat. Considering cost, it's importance, & ease of replacement, I always replace them rather than wonder if they're good or bad (consider it routine maintenance). Besides, who knows what's in there now. Changing the thermostat is one of the 1st things I do when I get a new (to me) van. Some aftermarket t-stats create overheating issues & that's a variable the van doesn't need.

If you wanted to test your t-stat, you would remove it and do a visual inspection. If it's open when cold, then it's junk (throw it away). If it'd closed, then drop it into a pot of water and place it on the stove. Put a thermometer in the water and heat. The thermostat should start to open when the water gets to 180 deg F & should be fully open before the water gets to 200 deg F. Tim