• Replacing your van's thermostat

    Modeling for all but one of the following pics is PJvan, a 1984 LE 2WD.

    New parts:
    Toyota P/N 90916-03046 (all vans)
    DO NOT buy aftermarket; sole known exception is the Prestone Generation 2 t-stat

    Thermostat gasket
    Toyota P/N 16325-63010 (all vans)
    It does not come with the t-stat! (I don't know if aftermarket gaskets are a problem per se, but the one bad t-stat gasket I've encountered was aftermarket ... )

    Optional parts:
    Lower radiator hose if it's at all suspect, ie, soft spots, bulging, etc … also will be necessary if the hose has bonded to the radiator and must be cut off.
    for all 2WD vans — Toyota P/N 16572-71010
    for all 4WD vans — Toyota P/N 16572-73040
    On other vehicles, a seemingly good older lower radiator hose can soften when hot and collapse from the suction pressure generated by the water pump. I don't know if the vans will do this; I intend to never find out.

    The Job

    First, drain the coolant from the radiator and then the engine block.

    While you're waiting for the coolant to drain,

    Go ahead, ask me how I learned this ... (12V may not kill me, but RoseyCoyotevan sure tried ... )

    Put the NEW gasket on the NEW thermostat; these two pics show
    the gasket started on the rim ...and the gasket in place; Toyota's "jiggle valve" shown

    change_t-stat.02_a.jpg and change_t-stat.03_a.jpg

    Check the gasket carefully to make sure it is COMPLETELY seated. I have had one try to fool me. It would suck to have to do this all over, right?

    After the coolant has drained, close the radiator and engine block drain petcocks.

    Here's where you'll find the old thermostat on a 2WD ... and on a 4WD (1989 shown ... thanks, Skyler).
    This is when you either wilt at the apparent impossibility of access, or rise the the challenge. Seriously, if a rookie can do it (it was my first "van repair"), it can't be that hard.

    change_t-stat.05_a.jpg and change_t-stat.06_a.jpg

    Remove the upper end of the lower radiator hose. Hold the end UP to keep the coolant from pouring on your alternator. If you will be replacing the lower hose, remove the lower end first, spilling out the coolant, and then this upper end won't have any coolant left.


    Remove the upper/front nut using socket wrench, 3" extension + 12mm socket


    Same tool set-up, going after the lower/back nut. Sometimes the alternator wire wants to get in the way. Regardless, squirrel the socket out VERY carefully and the nut will stay in the socket.


    Pull the housing straight out ...


    ... paying attention to the orientation ... it is NOT symmetrical. I've not tried installing it backwards to see what will happen because I suspect Toyota made it asymmetrical for a good reason, and it should be re-installed just as it was.


    Old thermostat in situ. Note that PJ's old t-stat is installed incorrectly, with the jiggle valve down. Pull it straight out; it may be kinda stuck in there and require a tool to gently pry. NOTE: it is NOT as easy to visualize in real life (unless you are a goose or a snake), especially on a 4WD; the camera is at an advantage here.


    Inspect the rim carefully for hunks of old t-stat gasket and remove them (or it will leak when you're done). Note the amount of coolant sitting inside. I jack up the front end of the van to access the engine block drain petcock, and leave it jacked up while I replace the t-stat (makes a good working height for me). I don't get much more than a few drops coming out this way. IF you have the van level, I do not know how much more coolant might come out. IF you cannot get the engine drain petcock to budge, bag your alternator or, better still, remove it. The first t-stat replacement I did was on someone else's van. That person was in a hurry and insisted that I proceed without either draining the block or doing something for the alternator. Two weeks later, the van was back in my carport ... getting an alternator.


    First, make sure your tools, nuts, and housing are in reach. Place the new t-stat in the block with the jiggle valve at 11 o'clock. VERY CAREFULLY place the outer housing over the bolts and t-stat and HOLD IT ON FIRMLY. Even if the old t-stat needed a pry, these things are really just barely balanced in there, and delight in falling out juuuuuust as you think you've got the housing seated. (I’ve been told a small amount of Vaseline on the gasket before insertion will help it stay in place; I’ve not tried that yet myself.) If you're not sure it's on right, do it over. Plan to do it over about a dozen times and you'll be pleasantly surprised when it's only half-a-dozen or fewer. (My first t-stat replacement was first-time right ... that sure spoiled me!)


    Make sure the housing does not rock (indicating improper seating of either t-stat or housing). WITHOUT releasing pressure on the housing, get the upper/front nut on (yeah, it's tricky and helps if you have skinny hands). Get it on far enough that the housing can't shift on that side, and go for the nasty lower/back one (this is where the housing likes to shift, the t-stat drops into the gap, and you cuss ).

    IF at any point when you're tightening the nuts it feels like it's tough to turn but not because it's as far as it will go, STOP. It could be because the t-stat has slipped and you're squishing the gasket (if you really squish it, you will need another gasket). You also do NOT want to cross-thread these bolts. Just be patient and focus on getting it right. Yeah, I know it's "more fun" on 4WD. 4WD is just more fun all the way around; that’s why you own it!

    Replace the alternator if you removed it. Replace the lower radiator hose. Add coolant. YIPPEE!!!!
    This article was originally published in forum thread: Replacing your van's thermostat started by llamavan View original post