OVERHEAT PROBLEMS (I'm Lost)

[firebiz16]

I have a1995 Toyota 4runner 3.0. the water pump, t-stat, timing belt, plugs, wires were replaced last week. The radiator is fairly new too. The problem is, it can idle for an hour and stay at normal operating temp. I drive it for ten minutes and it starts to overheat. I've noticed that I can put it in neutral and rev to 4000 rpms while on the road and the temp gauge goes right back to normal. The head gasket was replaced about 2 years ago. I'm not getting any white smoke or loosing any coolant.

The check engine light is on due to a faulty "knock sensor" which does make it run rough, but I don't think that has anything to do with the overheating.

Thanks

 

[A.Wilson013]

So basically, when it's in gear, it over heats?

Is it an auto or 5spd?

 

[firebiz16]

yeah pretty much when in gear at low rpms.

 

[SV_Dude]

Have you stopped to physically see if it's over heating? I mean, open the hood and feel the heat coming off of the motor? It could be a bad temp sensor.

 

[firebiz16]

Yes, you can actually hear it boiling in there. I have noticed the top rad hose is a little soft and Ive tried every thing I can to remove air from the system.

 

[SV_Dude]

So when it gets hot and you pull it out of gear, how long does it take to cool down?

It seems very odd that just pulling it out of gear cools it down... even while revving it up.

 

[firebiz16]

It only takes a few seconds to bring the temp down. I drove it yesterday to check again and itseems that once it gets hot from driving, it keeps creeping back even at idle too now.
I've noticed that the upper rad hose expands and contracts when reving the engine also. It almost seems like some sort of blockage, but it sems like it would run hot at idle all the time if this was the case.

 

[my92t4r]

sounds to me like a blocked or clogged radiator. Check the flow at the radiator. gl

 

[SV_Dude]

I guess this may be a good time to have your coolant system flushed.

 

[Bear_F_ucker]

This same thing happened to my friend a couple of years ago, and it took us forever to figure it out, but we put the thermostat in upsidown

Bear_F_ucker

 

[fourwd1]

It only takes a few seconds to bring the temp down. I drove it yesterday to check again and itseems that once it gets hot from driving, it keeps creeping back even at idle too now.
I've noticed that the upper rad hose expands and contracts when reving the engine also. It almost seems like some sort of blockage, but it sems like it would run hot at idle all the time if this was the case.

When you rev the engine the water pump works harder, so there's more pressure, which could explain the hose. But don't rule out an old weak hose either.
The hot spike sounds like temp overshoot, which isn't uncommon, could be a cheap t-stat, in wrong, jiggle valve position ...

 

[Sirceficus]

if you were to bring it in to the shop, i'd put a thermostat in it first. with a coolant flush.

 

[dawudih]

This same thing happened to my friend a couple of years ago, and it took us forever to figure it out, but we put the thermostat in upsidown

Bear_F_ucker

:withstupid:
defective thermostat most likely; possible air in system if you didn't burp it properly.

 

[firebiz16]

OK, I replaced the thermostat and new upper rad hose and another flush, same thing keeps happening. The only thing I'm not sure on is the placement of the thermostat. I placed in the the horizontal position, not vertical if that makes sense. Surely it's not upside down. I placed it in with the long or bottom end of it into the block.

 

[firebiz16]

What will happen if I take the T-Stat out and run it without one? Can this damage the engine?

 

[nashville67]

running with out a t-stat will make it over heat more because there isnt enought time for the heat to transfer before the water moves

 

[SV_Dude]

running with out a t-stat will make it over heat more because there isnt enought time for the heat to transfer before the water moves

Explain this a little more please.

From my understanding, there are certain temps of thermostats for a reason. Basically to keep the engine within a target heat range.

In my mind, running without a thermostat will cause the motor to run too cool... Not heat up to the proper temp range to make the motor run most efficiently. kind of the opposite of what you're saying.

*EDIT* Found from a quick google search:
Auto Upkeep - Frequently Asked Questions about Automotive Cooling System

For the clicky impaired