ripping my h$air out because of overheating

R

run4yota

New member
hi everybody, i have the most frustrating problem in the world, maybe someone can help me with.

about a month ago my engine was over heating. thinking it was mostlikely the thermostat i replaced the thermostat and took it for a drive, later that day it overheated to the point that my head gaskets failed....

so i rebuilt the motor from the bare block up (including new water pump).

now that i have it together i cannot drive it without it overheating, thinking it was the fan clutch (which was worn anyway) i replaced it. it helped, but i'm still overheating. so i replaced all the hoses (maybe something was clogged) no dice, still overheating. i replaced the radiator with a brand new one... still overheating! i am burping it by starting it on a hill and rev it a little then top off, rev a little, then top off again.. but nothing seems to help! :wtf:

my only hope at this point is replacing the thermo (which is only about a month old) i'm wondering if it got so hot that it was damaged.

i am open to ALL suggestions, and any advise, i've never come across anything like this in all my years of working on cars.

it only overheats at low rpms, as long as i keep it around 2700 or higher it runs a few degrees on the cool side.

thanks in advance everybody! :bigok:
 
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3vze (just rebuilt with new heads w/ oersized valves)

replaced parts:
radiator, thermostat, all hoses, water pump, fan clutch. i dont know what else to check or replace, it runs fine as long as i keep the rpms up, the second that i come to a redlight tho it starts to climb on the guage.
 
fan shroud fully intact and atached properly. condencer coil was backwashed with a hose when the radiator was out, and i checked it.. clean as new... i'm so puzzled, what would cause a car to overheat at low rpms and high rpms but right between 2700 and 3200 it runs fine? i'm wondering if it's a faulty sensor and it's saying that i'm hotter that i really am. but the sensor was working fine before the head gasket job.
 
To be honest, I'm new to the 4 runner scene, but I've experienced some problems similar to this with another car. The problem I ran into was that there were pockets of air in my cooling system. These pockets created dead space that prevented the water pump from functioning properly. On my old car, I cured this by leaving the lid off the radiator and 'pumping' the coolant through by squeezing and releasing the coolant hoses until I could feel nothing but fluid going through. Once you get that sensation, keep pumping a bit longer. You want to make sure you give all of the air a chance to work out of the system.
Again, this was not a 4 runner, but hey, it's a free solution that may at least lead you to the correct answer. Good luck!
 
yeah thats exactally what i heard for a few other sources, i've been doing a pretty extensive effort to remove all the air from the system (going on and incline, using a purge cup, ect. but nothing works... something odd tho, this morning i went and checked, and the radiator was low and the coolant resevior was overfilled, i'm thinking an air buble issure that may be partly due to a faulty radiator cap. i will try squeesing the hoses some more and see what happens.
 
Bad radiator cap. Coolant needs to build pressure to gain cooling power. Your cap is letting coolant blow by into the reservoir at the same time letting pressure out of the cooling system. The cap should hold about 13-16 PSI.
 
i'm going to go get a new cap and top it off, then see how she runs. (whats the worst that could happen, i already replaced everything else) lol
 
put new cap on, no dice. i jacked the car up so high it looks like it's doing a wheelie and ran the car till it got hot. now i guess just sit and wait. hopefully in the morning my coolant resevior is empty is empty.
 
the top radiator hose is hot, but no hotter than normal. the bottom hose is pretty warm, but not cold. the hosed that are hot are the hoses going to theheater core... omg they are like grabbing a iron. they also are what circulates the water through the coolant temp sensor bank... possibly air in those lines? the heater works good though! hmmm i'm hoping after sitting for a night jacked up in the front that the bubbles worked their way out as it cooled
 
run4yota said:
the top radiator hose is hot, but no hotter than normal. the bottom hose is pretty warm, but not cold. the hosed that are hot are the hoses going to theheater core... omg they are like grabbing a iron. they also are what circulates the water through the coolant temp sensor bank... possibly air in those lines? the heater works good though! hmmm i'm hoping after sitting for a night jacked up in the front that the bubbles worked their way out as it cooled
Click to expand...

OK it sounds like you have good flow. If it were actually overheating the upper radiator hose would be blistering hot. Radiator, water pump, T-stat are out. What has got me curious though is why your heater hoses are soo damn hot. They should be around the same temp as your upper radiator hose maybe alittle hotter but not scolding hot. Maybe you have a blockage in a water jacket? Sounds like coolant is staying static in the block somewhere. I know i'm reaching but there isnt much else it could be. Might be something just letting coolant trickle by too. I do know that doing a 3.4 swap would most definitely take care of it though. There isnt a whole lot to a coolant system and you have replaced everything except the block and heater core. Heater core has hot lines on both sides plus the hot cold switch cuts off coolant anyway so that can be counted out. Get a temp gun and take readings to make sure its not electrical. Thats all i got man, hope something comes around.
 
i am now kicking myself in the ass for not doing the 3.4 swap.. i just finished rebuilding this motor and between all the parts and the custom work i had done on the head for some performance(which is Very noticible) i have just shy of 1700 into it! :(... i coulda paid my buddy to put in a 3.4 for 2000... ugh hind sight is always 20/20... i got this tho.. my coolant bypass hose going from the temp sensor manifold to the block was clogged so the only way for passing water by the temp sensor is by going through the heater core... which looks severly corroded from what i've seen.. is it possible that the water in the coolant temp sensor block is sitting close to static because of blockage but when i rev the motor over 3000 rpms the extra pressure is forcing enough water through there to cool the temp sensor off?... it's pretty far on the probability side of things, but like you said... what else is there to check.
 
Sure... you have one of these off the wall problems. If it were me I would start taking things apart in that area. Take your heater hoses off and put a garden hose on one to make sure you have good flow through it. There is a gremlin hiding somewhere and you have to find it. Luckily you already narrowed it down to the general area. Only thing it really can be now is a blockage in the block or somewhere near the sensor.
 
hi anyone who may be in need of assistance with a motor that overheats after putting on head gaskets... i just wanted to post what i found out. i replaced the head gasket, water pump, radiator, thermostat, all hoses, sensors, and radiator cap... the problem turned out to be the head gaskets that i bought (evergreen products brand) were knock offs that were made upside down and flipped. so some of the ports were blocked, i havent torn it down and replaced them yet, but found from other posters that if you cut the cut the guts off of the thermostat it will run perfectly at norm operating temp (it just takes and extra 3-4 miles of driving to reach NOP) i like in phoenix and i drove 30 miles today with the a/c on high and not once did it go over NOP.

soo i will leave this post with this... how safe is it to run the motor with the thermo cut open like that? i could not care less about the head gaskets blowing because i plan on changing them any way as soon as i get the money to invest in some genuine toyota parts. but in the mean time for a few weeks is it safe to run like this?

if your wondering about the flipped head gaskets, google "flipped upside down head gaskets 4runner" and you'll see the post.
 
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