i recently purchased a 1998 Toyota 4runner with 259,000 miles and a fully rebuilt engine (5vz-FE) + rebuilt transmission. The 4runner is having an overheating issue ( with a 100 miles on the fresh build) it has had the overheating issue ever since the rebuild . So i have replaced the radiator, thermostat (OEM from Toyota .This is the second thermostat that i have had and tested both of them) , water pump , top and bottom coolant hoses, checked the timing , burped the system and it still overheats. I think that it may have something to do with the oil cooler but I am not certain about this. I would greatly appreciate your ideas or opinions about this issue because i am running out of things to do.

 

do your fans operate properly

 

yeah i forgot to add that in the description but it also has a band new fan clutch

 

Welcome to my hell. Were the headgaskets replaced? Ive done everything only to determine that i more than likely put headgaskets on backwards...... Now i have to go back in and do it again. Sucks.

 

yeah im pretty sure the head gaskets were replaced the right way because it isn't spewing from the radiator and hold the fluid fine. ( i bought it with the rebuilt engine and the guy i got it from gave up because of the overheating issue , but before i bought it i looked at the head gaskets online to see if you could some how get them mixed up and i didnt think you could.)

the weird thing is that i put a gutted thermostat in it and it ran fine without overheating

It will run all day in park with the temperature gauge on normal like it should be but when you start driving it , it wants to overheat.

 

does it feel like it has good power? it sounds like u have some blockage somewhere that is causing the motor to not get water everywhere. or it could also be a plugged cat. making it run warmer, u could also see about getting cooler plugs and running a set to see what that does.

 

ill see about some cooler plugs tomorrow, but it has a new catalytic converter in it and i even disconnected the exhaust to see if that was backing it up but it still gets hot , when i test drive it, i never let it get passed 3/4 of the way on the temp. gauge because i dont want to risk blowing the head gaskets.

put is seems like it is not lacking any power

 

if u are just using the stock gauge to see it over heating i would then get a temp gauge set and run that to see if u get the same results. it could be something that is making it get a false reading also use a Lazar temp reading tool and hit different spots around the motor and see if some places are hotter then other, its just weird that its over heating when running but when sitting still it doesn't,


just googled overheating due too air/fuel lean and came up with this page, might be something also to check. might just need to have a person with a microgas check it. look down and u will see a part on air/fuel ratio.

http://automotiveu.com/SolvingOverheating.htm

 

I ran the OBDII on it and it came up with the error codes p0300 and p0302 but i dont think running with a misfire would be enough to overheat the engine. Also i checked all of the spark plugs today and they look good , but im about to order a new coil pack.


I am still leaning towards the oil cooler line on the water pump housing. Could it be that this line is keeping the coolant low enough temp. not to open up the thermostat ??

Need some more help finding the problem though, I am out of ideas

 

Having same problem. Any update as to the solution here?

 

Timing could be off, like timing belt off a couple teeth. Turn crank to tdc, pull upper timing cover to inspect cam marks. Could be running pig rich if retarded. Radiator cap might not be holding pressure. Have you done a leak down test- I'd start there. Head gasket could still be installed backwards, and it's a very good possibility. They WILL go on the wrong way. Getting cooler plugs is silly, don't do that, stay with appropriate heat range BKR5e copper core. You don't need bandaids you need to fix the root of the problem.

 

3/4 of the way....yikes. That means your water temp is probably around 240 degrees. You have an obd2 port so you're a prime candidate for a scangauge2. It lets you monitor 4 parameters at once and you will be surprised how big the dead zone is on your existing onboard temp gauge.

http://www.scangauge.com/

good deal here
http://www.ebay.com/itm/ScanGauge-SG...075970&vxp=mtr



circled in yellow.... 50 degrees change in temps and the needle is "dead"