After a few miles of driving on the highway, steam started suddenly blowing out the hood and temp started to rise. Turned on the heater but out blew cold air. I just had the water pump, thermostat and timing pulleys and belt replaced about 200 or so miles ago. It started running rough when this happened so I do not think the heater core could be blocked. My two guesses are maybe a defect thermostat or blown headgasket.... any one have any ideas?

 

Could have been air in the system that caused it to overheat.
Once the engine over heats though, the possibility of a warped head is there and that can result in a blown head gasket.

 

What engine is this?

Don't immediately assume that you blew the head gasket.

I overheated an hour and a half from home, kept coolant in it as much as possible and got home. Ran a pressure test on it, and found a leak from the timing idler.

Fixed it and it still runs fine, no gasket problem.

 

Where was steam coming out of?

[QUOTE=zanzabar0;52147116]Turned on the heater but out blew cold air.[QUOTE]
Yes, either air in system OR steam was your coolant vaporizing, leaving no hot coolant in heater core.

How about your radiator? Good? No cracks? Fan Clutch engaging?

 

Its the 3.0, steam was coming out the radiator cap and egr tube where it meets the egr body via the nut, the nut hasn't been screwed in for about two years and its overheated before and hasn't come out there. Radiator was replaced last year all good

 

Hmm, might be the thermostat, or the water pump itself. How far did you drive it after wards? I had a water pump go at highway speed, and it blew a crack in the radiator (plastic tank).

Test the thermostat first, but you might have to dig further.

 

I probably drove a solid half mile no more than a mile at around 40-45. I'm about to go out and check through things now. How would i go about testing the thermostat?

---for some reason my sig wasnt showing up earlier...

 

You'll need a meat thermometer, or equivalent...

THERMOSTAT INSPECTION
HINT: Thermostat is numbered according to the valve
opening temperature.
(a) Immerse the thermostat in water and heat the water
gradually.
(b) Check the valve opening temperature and valve lift.
Valve opening temperature:
80 – 84
C (176 – 183
F)
Valve lift:
8 mm (0.31 in.) or more at 95
C (203
F)
If the valve opening temperature and valve lift are not
within specifications, replace the thermostat.
(c) Check that the valve spring is tight when the ther–
mostat is fully closed.
If not tight, replace the thermostat.

 

Also, before I got on the highway around town and stuff, at idle no heat would blow but at speed and driving it would crank it. Idk if that would add to the possibility of air in the system or heater core or not

 

tested the thermostat everything was within spec it opened and closed fine springs were good. The oil on the dipstick looked regular but the bottom of the fill cap was that light colored foamy sludge.

 

So after i put the tstat back in, i started the truck up and it idled around 2000rpm for a bit until reaching normal temp and made it back down to 800-1k area. Still ran roughly and the only area steam was coming out of was the rad cap opening, i didnt have the cap on. White, sweet smelling smoke was coming out the exhaust and exhaust leaks. The temp gauge didnt read it was real hot but it was around 3/4 of the way to redzone. Tomorrow i am going to try pressure testing the cooling system and a compression test on the cylinders

 

With engine cold, did you try running with radiator cap off? When engine is cold, there is nothing to pressurize the system. If you see bubbles and coolant wells over, while still cold, it must be exhaust pressurizing the cooling system, through a break in HG.

Good luck. I just had head gasket go bad on me at 185k miles. The truck had crack in radiator when I bought it so chances are it had overheated while in the hands of P.O. After engine rebuild and replacement of ALL coolant path and components, she runs well.
Last thing I need to replace is Fan Clutch (aka fluid coupling). Seems Ok but I want brand-new and OEM (Got an Aisin)

 

I did have the cap off when it was running. It wasn't at running temp but wasn't cold and steam was just pouring up like a steam train engine. Coolant never welled over just steam. I've gotten down to just about my last penny after putting alot more into the truck then I anticipated since September so I'm really hoping it isn't the hg since it's my dd and I'm almost broke lol

 

Those are the symptoms I had when my water pump went.

 

Are those common at all of being defective after just being replaced and brand new?

 

OMG! Sorry but where do statistics point to on a 3.0?

Gotta be thorough and do all tests. How hard it is to do the test with radiator full and engine cold? Would it cost you a penny? It will only take you a few minutes. why skip such a simple test?

Gotta find out the real root cause, not what you want to hear or believe. Otherwise, you'll be throwing money/replacing the parts that will not solve the problem.

If you do test like I mentioned you WILL verify IF it is the HG - or eliminate it as suspect.

I took my truck for overheating to a good Toyota specialist, they did best effort to diagnose. Then, I paid over a hundred bucks having coolant path un-clogged. However - a resounding however- it was I myself doing test ^^^ that diagnosed the root cause.

Of course, if water pump is bad, you will overheat, and this time coolant boiling over will cause the overflow.
To verify if HG try test above with engine cold.

 

At this point, you need to do a compression check...

 

I didn't see your post earlier, RAD4runner, until I came inside and responded so I did not know to do it cold. When I have more than the few minutes I had today, tomorrow I will do the test mentioned as well as a cooling system pressure test and compression test if needed.

 

Wish you luck, Man.

 

I did as your test said with engine cold and coolant popped out. I did find a piece of the orange gasket sealer the shop who put the water pump and other stuff in, in the radiator if maybe it means the water pump is compromised or its just the excess from sealing it. Thanks everyone so far for helping me out!