i have recently swapped motors in my 88 4runner. it runs good but has no heat an also runs cold after you start to drive it. i checked all the lines an the thermostat nothing was wrong there. also the top radiator hose feels as if it has way to much pressure built up in it. if anyone has any ideals on why please let me know. its a v6 3.0 if that helps to

 

Explain what 'runs cold' means.

Not having the hoses hooked up properly would give no heat.
Pressure in top hose sounds like the engine is actually overheating.

Possible air in the system.

 

when it idols the temp gauge shows its running at normal temp. but when I go to drive it the temp gauge drops as if the motor was off. I checked all the hoses an they are all on the way they are supposed to be, I believe its the heater core is why im not getting heat but im not sure

 

It's an 88. That's what the temp gauge does normally.

No heat means there's most likely a problem with the heater. Not the engine. And it's pretty hard to get the hoses routed wrong. They only fit one way. They're either too short/long, or not bent correctly to easily go where they shouldn't. It's probably the heater core, or the heater controls.

It's a pressurized system. Therefore, there's supposed be pressure built up in it when the engine's hot. Unless there's so much pressure that it's forcing coolant passed the radiator cap, then it's not too much.

 

My 89 4runner temp gauge never moved up an down like that tho. An I know its a pressurized system but it feels like there is to much pressure built up. I let it sit an idol for a good 20 minutes to let the air out of the lines.

 

Get the nose of the truck as high as possible and run the engine with the cap removed for a little bit. Obviously it has to be cold to remove the cap first.
Turn the heaters on full blast and try to burp any trapped air out by squeezing the various hoses.

 

Okay thanks. I will defiantly try that

 

these temp gauges can be very inaccurate.

warm it up good before you raise the front end, and you won't have to let it idle so long... catalytic converter manufacturers warn against idling for extended periods of time, it's somehow bad for the cat.

i personally don't believe in the trapped air theory, what i would do is warm it up and see how the heater hoses feel, if coolant is going through them, they should both be hot.

the valve controlling the heater core flow might be stuck closed.

 

I recently (this weekend) had the exact same symptoms in my 87 4Runner. I had completely rebuilt the engine at great expense. My problem turned out to be a bad thermostat. My engine is a 22RE which is different than yours, but exact same problem(s) - no heat, seemingly high pressure in outlet hose (top hose).

I figure that since the thermostat was not replaced during the rebuild it was pissed and decided to fail.

 

Well I tried lifting the nose of the truck as high as possible still having the problem. Maybe it is a bad thermostat so sometime this week ima go buy one