So, my 1994 4Runner 3.0L has been having some minor issues staying cool. For a long while, it was just a matter of when I'd see the temp gauge go up towards the red, I knew that before I drove it next, I needed to add some coolant. This totaled to about 1 x 3 qt. bottle/month. Then, a couple weeks ago, I was driving to work, and it overheated. When I went to fill up the radiator, it was totally dry. Added around 5 L of coolant, and went on my way. Almost happened again on the way home, but I was keeping an eye out that time. So, for the last couple weeks, I've had to refill it every time I'm stopped for more than an hour or so. Approx 6-10 L/day. Time for just water until I get this fixed!

I was OK with this for a bit, but knew that the cooling system needed to be fixed. Picked up a new radiator, as I knew the old one needed replacing, and replaced it, along with new hoses and hose clamps. Filled the system up, drove a bit, and topped it up. Then took off down the road. Figured a few miles up and down one of my favorite drives should help things out, show me if there were any issues. While I was driving, it would start to squeal when coasting in neutral, but it'd been making that noise for a while, in certain temperatures, when started cold. The squeal when started would disappear after 10-20 seconds. Not the case now that I'm driving it. Every time it'd be running in neutral for more than 30 seconds or so, it'd start to squeal.

Made it to the end of the drive, was turning around, and it started to get hotter than normal. Pulled over, got out, and there was water just spewing out from under the engine. After letting her cool off for a couple hours, I went to fill the system back up so I could get her home, work on her there. Well, every time I added water, it would just start leaking like crazy from (what looked like) behind the thermostat housing. I leave her parked, go to autozone, and get a new thermostat, housing, and gasket. Get those replaced, and try again, with the same results; water just dumping out from behind the therm.

I've asked a few people, and the general consensus seems to be that it's the water pump's bearing has seized/blown/doesn't work right any more.

My question is three-fold. One, does this seem like the likely culprit? Two, if it is the water pump, should I be picking up the one with or without a bypass tube? What does that do, what purpose does it serve? And three, if it's not the water pump/gasket, what do you think it is? I'll give any more insight I have on this. Should you need it, just ask.

As always, thank you folks in advance for any help/advice.

 

Definatly sounds like water/coolant pump failure.

Squealing noise is likely the timing belt gliding along a frozen water/coolant pump pulley.

The thermostat mounts to the face of the coolant pump and the "weep" hole is near the thermostat area.

Water pump and timing belt job in your future.

There are two different coolant pumps for the 3VZ-E. One with oil cooler and one without oil cooler. Just identify and then make the correct purchase.

 

Water pumps have a limited lifetime, just like the timing belt. Supposed to be done every 100k miles or so.

In the future... don't run pure water. I know it was just to keep it running but water has a much lower boiling point than coolant. Once it boils you've got a whole lot of pressure building up in the system and it'll find a way out, even if that means breaking seals and hoses in the process. Could even bust a head gasket that way if it's weak.

Before the massive burst, did you see any other coolant leaks? They are marked by the white chalky residue they leave behind, or if the coolant was bad it'll be rust colored.

BTW... did you ever take off a whole lot of hoses and then put them back on? Any chance you or the previous owner might have connected a coolant line to something it's not supposed to go to?