Don't hesitate to doubt my mechanical ability lol . Although, I've built and installed three of these motors now and I'm confident all hoses are correctly routed. I'll repeat the test hot and see what I can find.

 

You're one ahead of me then Hope you can find it!

 

I don't have the same model, but had a similar issue of loosing coolant with no visual explanation & no leaks when pressure testing. Turned out under operation the water pump was releasing coolant which was evaporating off immediately.
Track down your water pump and inspect visually around the seals for any signs of calcification. With the vehicle cold start it and visually check the lower side of the pump area to see if any wet spots appear before the motor gets hot. Worth checking.

 

How old is the head? Is it the original head? The reason i ask is because i had a similar problem on my 1991 toyota pu 22re engine back in 2000. This issue started with about 130,000 miles on my truck. I bought the truck brand new in 1990. It had been loosing water at a slow rate at first. As the months went by i had to keep adding more water each time, and after a year or so, i was adding water every day. Even though i did shell out the money for a Stant pressure tester and the adaptor for the toyota radiator, i still did not find the leak. It was not until during the summer months that i finally noticed steam coming from the tail pipe. I called a shop that rebuilds engines, Adams Machine Shop in Lancaster, CA, and they told me that the water jacket eats into the exhaust port in the head at the #4 cylinder area. I took the head off and brought it to them and they did a pressure test which confirmed it. I bought a new head and it solved my coolant loss issue. Hope this helps, Todd

 

No idea how old the head is, I bought it from a friend of mine out of his (I kid you not) bin of probably 30 22r heads. It was fully reconditioned, machined, and pressure tested 10,000 miles ago when I built the engine. I'm now 100% sure there are no leaks hot or cold. Still at a total loss.

 

Whelp, still haven't found anything. I fixed a few leaks that showed up only under 25+psi, so maybe somehow that will help. For now i'm just keeping the radiator and reservoir full and checking it every few days. I'll keep this updated.

 

I'm in a similar boat... my 1990 4runner new motor and new radiator, new hoses (except to heater cores.. hmm) loses a small amount of coolant over time. my 94 does the EXACT same thing, I put a new rad in there too... I just top the coolant off when I change the oil now . maybe I'll get ambitious and check all the heater hoses

 

Well, it's still losing lots of coolant. I don't see how it could be the head gasket and it's definitely not leaking anywhere. I'm going to pull the intake manifold off and check if it's warped. I'm thinking maybe a leak from the coolant passages to the intake on the head. That could jive with my symptoms.

 

Ive got a new radiator but have started to notice the same thing. None in oil, no drips or wetness. Hadnt thought of rear heat. Wouldnt it wet the floor like the front core will do in these? 88 runner 22re

 

Well, i just replaced the intake gaskets, didn't see anything that immediately looked like it was leaking, but there was some pitting and corrosion around the water passages on the head. So maybe it was leaking under the gasket through those. I put some copper RTV on this time, so maybe that will fix it. Time will tell.

 

Some minor pitting around intake/ coolant ports on head. I seriously doubt this is the problem, but i put some RTV on it anyway.

 

[SIZE=7]I FOUND THE LEAK!!!!!!!!

[SIZE=2][SIZE=3]So i went to check my oil yesterday and noticed that the oil looked slightly milky despite only having about 200 miles on it. "That's odd" I thought to myself. Losing coolant, no external leaks, milky oil. Sounds like head gasket, right? Well, no, it wasn't. I had already tested the head gasket and it was fine. There was no oil in the coolant. So i started to think about where else coolant could be getting in the oil from. It had to be somewhere where the coolant pressure was more than the oil pressure by a considerable amount. Cracked block/ head? I didn't think that was super likely as the motor has never been frozen, overheated, etc. Then it came to me. The timing cover. There's a gasket between the block and timing cover where coolant passes through to the water pump. That has to be it! So i popped off the valve cover, pressurized the cooling system, shined a flashlight down the length of the chain, and voila! Saw water dripping. However, it doesnt appear to be coming from that gasket. It seems to be coming from right smack dab in the middle of the timing cover on the back side. Now i have to figure out exactly where it's leaking from. There's no way to really see without removing the cover, which i would like to avoid, since it involves taking the head off (if you're doing it right). Here's a picture of where i see water dripping. Any ideas where it could be coming from? It's about 1 drop of water per second under normal cooling system pressure.

 

Well, i pulled the water pump and saw what looked like lots of little cracks in the timing cover, so i'm calling it low quality, crappy casting. Here's what i'm seeing:

There are lots of little cracks like that all through the channels in front for the water pump. They could be just casting lines, but they correspond to about where the water is coming from on the backside, so i put a skim coat of JB weld on the water channels under the water pump and i guess we'll see. It's been curing for a couple days and i'm about to go test now.

 

Whelp, that was it! Doesnt appear to be any more leaks! This was really a freak problem, but i'm really happy i fixed it before it got worse and left me stranded somewhere. For what it's worth, this was a brand new timing cover purchased when i rebuilt my engine less than a year ago.

 

Thanks for the info. Crazy problem. Cool that you figured it out. Where did you buy it from? Or was it og?

 

Very unusual .....good catch though!