dwest76

I have been reading countless threads on this subject, so believe me, I used the search function before posting this. Several threads have very similar issues, but maybe not exactly like mine so here goes........

I have an 87 4runner 22re recently rebuilt with AC. The heater on this truck has never worked well and recently stopped working altogether, just blows cold. the other night the CEL came on and I just got home as the boiling coolant was spraying everywhere under the truck so I begin my research here. It was throwing Code 4, water temp sensor. radiator and cap are 1.5 yrs old, thermostat is new. I burped the system suspecting air. flushed the radiator, no issues there. flushed the heater core, no blockage there. intermittent squealing noise from the water pump area so that's my next move.

To test I filled the radiator full and started the truck, heater on hot. ran for a while and the tstat opened and coolant moved. refilled with coolant and watched for a bit before putting cap back on. after running for about 5 min longer, the overflow was spewing again. not boiling, overflowing. Temperature gauge has been exactly normal through ALL of this, so I'm guessing it doesn't work.

so.....my question is, could the water pump be causing my no heat issue? or could this just be a defective radiator cap? I'm going to replace the cap today and take out the pump as well to check it out, I'm just looking for 'yep, that could be it' type of reinforcement before I start spending some cash on a pump. I'm leaving the HG as a last resort..............would a blown HG cause the heater not to work? I checked the fluids, there wasn't any coolant in the oil and no oil in the coolant. Until this first overflow issue all levels were fine regarding coolant and oil so I'm assuming no leaks (major anyway)

sorry for the 113th post on heater issues, I'm just wanting to get this thing moving again since it was my DD.

dwest76

water pump is fine.

dwest76

i replaced the water temp sensor so no codes now. also replaced the rad. cap. I really don't think it's overheating, just no coolant flow. as soon as it warms up the coolant is going straight to overflow and out.

any ideas?? I'm at a loss.

dwest76

I don't think so, tstat has been replaced.

dwest76

I guess a leak down test is my next move.

Is it possible that a partially blocked heater core would cause this? I ran a hose to the inlet and outlet to flush and clean water was coming out.........I can't help thinking that something is blocking my flow. You can watch the coolant leave the rad when the tstat opens then I fill it up (rad), but it doesn't seem like that coolant is going anywhere (after fillup). Maybe it is flowing underneath the coolant that is in the neck, but I wouldn't think so.

I read somewhere that if the overflow tube is bubbling (with rad cap on), that was a sign of BHG. I tried that last night on a cold engine and there were some very small bubbles that went away when I throttled the engine. When I let off of the throttle there would be a few and then it would even out again, so I think that may be attributed to the water pump pushing. When I was holding the throttle down the coolant was perfectly calm.

dwest76

bump for any ideas. I'm leaning towards HG, but this one only has about 10k on it (rebuild from engnbldr). Will be a couple days before I can do a compression test.