New to site but not new to 4 runners, this is my 4th one, over the years I have had 2 gen 1's and one gen 2 before this one.

I have a 1995 4runner with the 3.0vz

It had the heads and valves done 20K ago since that it has had new thermostat and then another new thermostat (OEM this time), a new water pump, new clutch fan, new radiator all this done by the previous owner.

When I got it still showed overheating on the gauge when at idle (after coming off of the highway) but what I noticed right away was that it never gurgled, boiled, smelt hot or felt hot. Heater worked great but the truck gauge shows 20% hotter with the heater core opened and the heat on then with the heater core shut off. Normally runs down the highway with heater core disengaged at 40% on the gauge but when you engage the heater core in seconds it jumps up to 60% and in seconds after disengaging the heater core it drops back down to 40%.

I was very suspicious of the fact that it did not seem to be hot when the gauge said it was so I had the shop shoot it with a heat gun. Radiator only running around 130, the hottest places in the cooling system were under 190 (mostly at the back of the engine. Heater blew at a constant 150 degrees in the car. I had the water temp sensor replaced with no change.

So the best explanation that I have seen for this occurrence said that it was a an line coming off of the coolant bypass outlet number 1 (hope I got that right, best what I can tell the coolant bypass tube is the one that runs along the top of the engine from front to back under the junk on top of the engine) that was likely partially clogged causing super heated water to not circulate past the temp sensor fast enough when at idle thus causing the temp sensor to get an incorrect reading.

So my question is, does this make sense (as a layman it does to me) and if so how would I clear that blockage or partial blockage, If not what could be causing these inaccurate readings?

 

you would be correct. time for new hoses. first i would flush the system thoroughly to get all of the junk out.

 

Thanks for the reply, The hoses may be bad but they do not seem spongy and seem firm.

My fear is that there is a partial blockage in the bypass pipe that runs down the center of the engine under the intake.

While a flush may get it out I am pretty sure (not positive but considering the work that has been done and how clean the coolant system looks) that it has received one or more flushes recently.

So my question is what is the best way to clean out that pipe (during a flush I assume) to make sure that it gets flow.