I have a 1996 3.4 V6 in my 1990 4runner. It runs great but appears to be inhaling coolant. I checked my engine oil and it's clean. I ran a block test to see if hydrocarbons were in my coolant and that tested negative. I also did a pressure test on the radiator and there were no leaks, but it would not hold pressure. I pumped it up to 13lbs and over 30 seconds it went back down to zero. I am afraid I have a cracked head or blown head gasket even though the block test came back fine. Anyone have any thoughts on this??

 

You've got a coolant leak if its not eating coolant. Either the water pump is worn and its weeping out from the weep hole, or its leaking at the heater hoses at the back of the motor.

 

Bottom line cooling system does not hold pressure you have a opening someplace.

That you just have not found!!!

Heater Core is always a good one.

Not smelling coolant in the cab at all?? No big Clouds of white smoke??

With a helper with the system under pressure from your tester look for your leak.

Just How much coolant you using ? A gallon on a ten mile trip?? A gallon a week ??

 

I presume the 2nd Gen 4Runner has a rear seat heater. If so, get under the truck and examine the steel coolant lines for rust.

7 or 8 years ago my friend stopped by with his '98 and mentioned that his overflow tank was always low. After some sniffing around, we noticed that the rear seat heater lines were completely corroded and weeping coolant. Our solution was to loop the supply & return lines together at the firewall - super simple. Of course this eliminates the rear heater, but it also eliminates a potential disaster.

So I've been driving another friend's '98 for the last week while I perform some surgery on my '01. Yesterday I rotated his tires, greased the driveline, and did an oil change. While under the truck, I noticed that his heater lines were thoroughly corroded as well. I pushed against one of the lines and was met with a shower of coolant. Long story short, I performed the same RSHD (rear seat heater delete) to his.










Andreas

 

For my RSHD, I cut one pipe by the firewall,removed other hose and stuck the cut pipe into the empty hose. Bypassed the rot with no parts needed.

 

If you look at my third pic, I took the upper hose, curved it, and attached it to the lower fitting. Simple.



Andreas

 

Another option: the coolant is leaking out of the bypass tube under the lower manifold.


See post 40 here.

 

Update: On Friday I took my 4Runner to my friends shop in San Diego. The first thing we did was a pressure test again on the cooling system. I realized that the pressure test kit I rented the last week from Autozone was junk. I pumped it up to 15 pounds and left it there for 30 minutes. Every 10 minutes it would lose a pound and I had no visible leaks. I told my friend at the shop that the check engine light threw a code of a misfire in cylinder 5. I pulled all of the plugs and they were all burning well except #5 was a little wet on the outside. I brought the #5 cylinder up and shined a flash light down the hole of the spark plug tube and I can see the top of the piston was wet. In the end my friend seems to think I must have a small head gasket leak or a cracked head. Next weekend I am going to pull the head off and check it out.

 

Uggh.



Andreas

 

I continued this topic on my build page


https://www.yotatech.com/forums/f199...runner-280025/