horunner1x

Bumping an old thread rather than making a new one even though this is super old.

1990 4Runner 22re,manual trans, 4x4, rear heat lines removed.
about a month ago when the temps started dropping a bit in SoCal I noticed my temp gauge in the morning wouldn’t reach the middle where it’s always gone. Afternoon drive home while it’s in the mid-high 70s it was normal. Only time I’ve ever experienced a drop in temp is coasting down the mountain in winter. Didn’t think a whole lot about it but the heater also wasn’t cranking real hot like it usually was. During this time I also noticed my water pump weeping so I swapped that with a new Toyota one and new gates hoses. Flushed my radiator and vacuumed out any sediment I could from the radiator. Temps remain normal but in the cold it’s not coming up to temp properly. This morning it was about 45° on my drive to work and the heat was warm, but not as warm as it was last winter, all the while my temp gauge staying at about 1/3 when normally it’s at 1/2. When I got to work I popped my hood and was able to hold my hand on the upper rad hose, but the radiator was a little too warm to keep my hand held there comfortably. Is it safe to say I need a new thermostat?

should I go with standard or a 2 stage? I’ll order it from 22reperformance rather than the dealership, they were a major pain when I got my water pump.

2ToyGuy

I would say thermostat is a very good possibility. Most thermostats are designed to fail open. IOW: if it's getting old and near, or at, the end of it's life, it will open all the way and stay that way. This could be the cause of the cooler than normal operating temps. It should open far enough to keep the water at a constant temp, opening and closing somewhat as required to achieve that end.

You can test it with a pot of water on the stove, and a thermometer that will read up above boiling by a fair amount, all the way down to "room temperature". Hang the thermostat in the water with a stick and string, or wire, and see where it opens, and closes. It should open completely as the water climbs above it's rated temp. don't let it, or the thermometer, sit on the bottom of the pot. You'll get false readings.
Of course, if you pull it out of the truck, and it's wide open at room temp, well, it's bad, no question.

Ok, ok, enough babbling. Yes, I would say replace the thermostat, and it's gasket. I would go with the two stage thermostat, especially if you have the situation where, when you are warming the engine up with the heater on, the temp gauge goes up well above normal range, then comes back down to the normal range. Especially if it "bounces" a few times, going a little high, then a little low, eventually settling at it's operating temp. The two stage thermostat will reduce, or eliminate completely, that situation.
DON'T forget to properly burp the system once ready to run the truck after replacing the thermostat. Important thing to remember to do.

Good luck, and let us know how things work out.
Pat☺

horunner1x

Thanks for the response, I’ve never had the temp go above half on the gauge, but it usually only take about 5-10 minutes to get there even with the heater on full blast in the winter. Lately it only gets to the middle of the gauge, even with heater off, once I get to work 15 miles away. Maybe I’ll stick with single stage since I’ve never had that problem with the bouncing gauge. Since this started before replacing the water pump I’d assume it’s not an air pocket, but I’ll triple check the burp later today. If it doesn’t help tomorrow morning I’ll order a new single stage from 22re performance.

2ToyGuy

You might be surprized at how these trucks can hide air bubbles in the cooling system. A quick way to see is to park it on a hill, or ramps, so the radiator cap is the highest point in the system, and let it run 20-30 minutes. Shut down, and let it cool off all the way, then check the radiator, and recovery tank, for proper fills of coolant. Often the recovery tank will be very low, and if low enough, there may well be air in the radiator, too.
Fill them both up all the way to proper fill lines, and drive normally, just keep an eye on the level of coolant in the recovery tank. You can give the upper radiator hose a squeeze with your hand to check for air in the radiator. If there IS air, you'll be able to squeeze it fairly easily, and may even hear "sloshing" from the radiator.

Anywho, I wish you good fortune!
Pat☺

horunner1x

I did it with the front end maxed on my jack with a 4x4 under it but I can always go park it on the steep incline in my back yard and let it idle for a while. Should I leave it there while it’s cooling back down till I open the cap again?

skypilot

iTrader: (1)

You really need the hill. Kinda like a poser shot. Anyway I have a basket of bad thermostats. I bet yours is stuck open. Or opens too soon because the spring is worn out. Anyway O-rings and T-stats are cheap. Replace both and the do the poser air bubble thing.

horunner1x

10-4 I’ll report back if a new single stage and poser shot burping doesn’t fix it, thanks guys.

2ToyGuy

Yes, you should leave it on the hill while it cools. At LEAST until it's done going up after you shut it down.
After running long enough to get fully warmed up, when you shut it down, the temp goes way up. It's called a heat soak. It can make air bubbles move around in the most peculiar ways. As long as the radiator cap is the highest point in the system, any and all air bubbles will make their way to it. If the pressure is still rising, they will exit through the cap to the recovery tank, and overboard. I've seen the level in the recovery tank rise nearly all the way to the fill cap during this period.
If the temperature is dropping, water will flow into the radiator from the recovery tank, but any air will stay in the radiator. Like if a bubble moves into the radiator after everything starts to drop in temp. Just remember the warm up period before it starts cooling down after the engine shuts off. That's why you want to open the radiator cap and check the fill level in the radiator once it all cools down. It's liable to be low on water. As is the recovery tank.
Make sure the recovery tank is filled up to the FULL line. Much above that, and it will likely dump water/coolant overboard as the truck heats up. It's really amazing how much the whole system expands as it heats up. Since water isn't compressible, it will flow out of the radiator into the recovery tank. If the recovery tank is too full to start with, it will dump what it can't hold overboard. Kind of a waste is all.

Remember all of this is after you get totally done with ALL the work involving the cooling system.

Good luck with it!
Pat☺

horunner1x

good info, thanks pat. Wonder if that heat soak you describe is why I get a low idle on start up when the truck has only been off for 5-10 mins. Like a quick stop. Enough time for the temp to jump up and make the IACV go real wide open? Ordered a t stat from 22re performance, was supposed to be here today but the tracking doesn’t really make sense. Hopefully tomorrow I’ll be able to tackle it.

2ToyGuy

Make sure the VSV controlling the vacuum going to the FPR is functioning correctly.
Essentially, there is vacuum applied to the FPR during normal operation. It comes from a VSV which is controlled by the engine temperature, which goes to the ECU. The ECU sends a signal to the VSV, so that it applies vacuum to the FPR. This lowers the pressure the FPR holds in the fuel rail down to 33--37 PSI, when the engine temp is below a certain point.
When the temp rises above the given set point, like during the heat soak condition, the vacuum to the FPR is shut off, and normal, atmospheric pressure is applied to the FPR. This raises the pressure in the fuel rail up to 38-44 PSI. This helps prevent the formation of bubbles in the fuel rail caused by the heat coming off the engine. If this system isn't functioning correctly, you can have troubles when the engine is hot.

You can check the system fairly easily, but you will need a fuel pressure gauge. Most people attach them to the cold start injector. Easy place to monitor fuel pressure. Right out in the open.
Then, when the engine is at normal operating temp, pull the vacuum line off the FPR, and see if the pressure jumps up. If not, bad FPR. If it does go up, possibly a bad VSV, ECT sensor, or ECU. Generally the ECT is the trouble, but not always.
Bear in mind, any time a crush washer has the items it seals up loosened off, even slightly, it MUST be replaced. That's three crush washers if you put a fuel pressure gauge on the cold start injector, and so on. It will take three when you install the fuel pressure gauge, two when you remove it. Always makes sure you have extras of every size you might need. You'll probably use them. They jump out of your hands and vanish. They malicious, and magical. It's amazing.

Having said all that, if the IACV isn't operating correctly, and is applying extra air to the TB when the engine is fully hot, or during a heat soak condition, it can cause problems, like those you're seeing. You can try pinching off the hose going to the throttle body when you're having those idle troubles, and seeing if the idle settles down and operates as it should. It's a fairly large hose, and right out in the open. You can use your fingers, or a sufficiently large pair of hose clamp type vice grips. Maybe a pair of those pipe clamp pliers. The ones where the jaws are adjustable, and angled to the handles.
Just be careful of the belts running right there when the engine is running.

Finally, and this would probably cause idle problems all the time, not just hot, but it's a possibility, the o-ring on the idle adjust screw. If it's gotten old, brittle, and cracked chunks off, which have gotten down into the air passages it controls, you'll have idle problems.
If you go to remove the idle adjust screw to check and clean the air passages, remember to screw it all the way down till it bottoms out, counting the turns and partial turns, it takes. Then, you can unscrew it all the way out, check it's o-ring, and check the air passages it controls. A shot of carb cleaner down the air passages is always a good idea, as long as you can get to them. A shot of carb cleaner down the vacuum ports on the throttle body, is generally a good idea. At least every few years.
A new o-ring is easy to find. They're everywhere. Apply thin layer of vaseline to the o-ring before installing the IAS. Makes for a better seal, and makes the o-ring last longer by a fair amount.
Then put the IAS all the way back in, and unscrew it to the point it was at when you started. It's a good starting point. Then set the idle normally, to about 800.
Remember, the Idle Adjust Screw is the smaller screw, under the larger size screw cap, on top of it. Not that *I* ever made that mistake. <ahem> Not me. No sir. No way. <ahem>

Might not be a bad idea to check and clean the PCV, and the EGR system. The EGR system gets clogged up after a while, due to the crud running through it.

Good luck, and let us know how things work out for you
Pat☺

horunner1x

poser burping shot

Okay so swapped in the new oem single stage thermostat and it warmed up quickly and stuck right in the middle. Parked it on the little hill in my backyard and ran it to temp, cooled, checked level, ran it to temp, cooled, checked level, and tbh the slow fill while running in my driveway worked Just as good as parking it on a hill I think? Didn’t hear any bubbling or have to add any more to the overflow or the rad. Think my overly cool system is fixed. Also exhaust didn’t smell like gasoline anymore cause it thought it was cold all the time lol.

I would know for sure till I drive it when it’s nice and cold out but it warmed up very quickly and stayed where it should.

2ToyGuy

I'm glad it was something simple and easy, like the thermostat.

Way to see if a two-stage thermostat would be good to have, is to start it up cold as cold gets. Turn the heater on full hot, fan going, as soon as you start it, and watch the temp gauge. If it climbs up above "normal", like to 3/4 or a bit more, even as far as just below the upper white line, then drops down either to, or below, "normal", then climbs back to normal and stays, a 2 stage would be beneficial. Not necessary, but would tend to stop the rise above "normal".

Toyota routed the return from the heater core to just before the thermostat. This tends to hold the thermostat closed longer with the heater on, than it would with the heater off (no "cold" water returning). Thus the temp goes higher than it would otherwise, before the thermostat "pops".

Anywho, glad it's working right, now. Watch the level in the recovery tank and radiator. It can still bubble some air out over the next couple weeks, if there is any. A quick check of the radiator's level, without opening the cap, is to squeeze the upper radiator hose with your hand. If it's relatively soft-ish, or collapses much, you have air in the radiator. Otherwise, you're GTG!

Enjoy your truck!
Pat☺

horunner1x

It was 43° this morning when I left for work, 4Runner warmed up very quickly and stayed right at the middle of the gauge for the whole drive. I think that thermostat has been tired the entire time I’ve owned this thing, it’s never warmed up so quick, only took 3-5 mins idling, usually takes 5-10 once I start driving. Thanks guys, pretty sure this is fixed and it’s due to yotatech! 🤙🏻

2ToyGuy

Glad it's fixed!

Now, go out and enjoy your nice, cozy, warm , truck

Pat☺