I just swapped out a new motor, aside from a hard start condition, I'm also getting a minor overheating issue.

New waterpump, new T stat, new coolant temp sending unit.

I notice that every so often, it overheats just a bit above the normal position. Typically (on the old motor and usually one the new) the guage sits at just below half, and now I occaisionaly see it get to just above half to maybe 2/3 up the guage. It will reach that level and then go back to normal pretty quickly. Its pretty random how it does this. It's not just under load. I really can't figure it out. I drove it 20 miles on the freeway and it didn't happen, then drove it just down the street and it did. I thought I might have some air trapped in there, but I put the truck on ramps and burped it with the heater cranking for a long while. I don't think there is any air in there. But I will say that I have only seen this condition happen with the heater control valve open.

Might this just be the "new" normal condition of this new motor, with the new cooling system parts? Or is there something wrong that is causing this?

 

I just put a new engine in too and mine was doing the same thing. I put in the duel stage thermostat and I have not had the problem since.

You can find it at the dealer.

 

Talk to me about the dual stage tstat. What does it do differently?

 

Was that part no 90916-03070?

 

my truck does the same thing.. yes thats the correct part number for the dual stage

 

It's really only a thermostat with 2 tempature valves on it. The small one is set at a lower tempature to let some fluid flow through until the water is hot enough to trigger the bigger valve to open at the correct tempature -195 degrees. The heater core puts the cooled water back into the system right before the thermostat and it thinks the coolant is cooler than it really is. In reality the coolant is hot and the thermostat should be open.

It's really the design of the heating system that causes it and not because your coolant system is bad.

 

I had the same problem and I put in a larger radiator. It helped but it didn't solve the problem completely. Maybe I should try that dual tstat.

 

I love Yotatech. It helps solve those little problems.

 

I just bought the new thermostat and gasket. Gasket looks like big O ring. Is that right? How does this thing seal the top half and the bottom half of the housing?

 

it sits between the thermostat housing

 

Yes, the o-ring is correct. The o-ring becomes compressed in the recessed area of top & bottom halves of the housing, thus sealing the connection. Trust the engineers at Toyota, it does work. Just replaced my thermostat a few days ago using the same procedure. It's detailed in the FSM.

 

Ok, I was just used to the flat style gasket that went between the two halves of the housing. I don't have a FSM so I'm hoping its self explanatory. Anything tricky to it?

 

Drain the coolant until it's below the thermostat housing to prevent it from going all over (all of it if your replacing the coolant). If the bolts don't want to come out, don't try and force the situation. Spray with your favorite type of penetrating oil and try it again. You do not want to break them.

When putting it back in, make sure the jiggle valve (little rivet looking thing) is facing the radiator. It will help when burping the system. Make sure it’s in the right way and put the o-ring on the outside of the thermostat housing. Fill back up and burp the system and you should be fixed.

 

Good tips. Thanks. But, "put the O ring on the outside of the housing? The outside?

 

You will see once you have the old thermostat out. The o-ring fits on the outside of the thermostat.

 

The rubber gasket should have a slit in the center that the thin metal of the thermostat fits into. You will have to stretch the rubber to fit it around the thermostat. Then it should seat nicely around the thermostat.

 

OK, well I changed out the tstat last night with the new dual stage. Drove it for 10+ miles and it was fine. Drove it to work 10 miles this morning and fine. Drove it home and after 5 miles or so it did it again with the brief overheat. Drove it for about 15 more miles on the freeway and it never did it again. WTH? Why would it do it just once and then be fine? I'm not sure if the new Tstat solved the problem or even helped at all. Thoughts?

 

Well you changed the t-stat, so you had to drain coolant. You probably have a little pocket of air somewhere. Keep burping it. 22res are a pain to burp.

 

your telling me

 

Well I guess burping is worth a shot but I really don't think that is the problem as the condition is exactly the same as it was doing before. Front tires up on ramps, rad cap off and heater blasting?

What I don't understand is why this never happened with the old motor. I'm not sure what kind of tstat it had in it before, but it never moved one bit above normal range.