Confusing Overheating and Intermittent Severe Coolant Leak

I've got a 2000 3.4 with 250k, timing belt was done around 170 so it's coming up on due.
About a week ago I wasn't paying attention (long day) and pulled into my driveway to the sound of coolant boiling. Temp got to about 270. Not good. Next morning I looked and coolant is low, of course. I topped up and ran it up to temp and was watching a steady drip, say 2 drips/second that looked to be coming from the water pump. Hard to tell for sure because everything was wet but it was def coming from front of engine and there's no way I can think of that it could have been running down from radiator or hoses and ending up in that spot. I shut it down and ordered a water pump/timing belt kit, figured I need to change that out and run it for a while to find out if I warped the heads.
So now the kit comes in and I figured I'd run it again to double check the leak is the water pump. Now, no leak. I drove about 15 miles round trip on the highway and I'm not seeing a drop of coolant anywhere. Power seems OK, truck is running great, not overheating, no exhaust smoke, no bubbling in the radiator on startup or coolant in oil or oil in coolant. Runs like there's not a damn thing wrong with it.
Any ideas? Is it possible for the water pump seal to give out enough for a pretty severe leak and then seal back up? Other thoughts?
It's about due for pump/belt anyway but I would hate to do all that work and then have the HG blow 50 miles later and have to tear into it again. I might just keep driving it until I can figure out what the problem is but I'm very confused. Any suggestions?

 

That was kind of long, let me sum it up -


1st Gen Tacoma, about due for timing belt / pump

Overheated, pretty bad. Leaking bad.

Next day I topped up coolant, had a significant leak, I'm pretty sure from the water pump

No symptoms of blown HG (yet)

Let it sit a few days, got the parts and drove to shop - now there's no leak

Ran highway speed about 15 min, still no coolant leak, no HG symptoms (yet)

Why would it leak that badly (2-3 drips/second) and then stop completely? This was the next day, when it had cooled. Leak started as soon as the thermostat opened. Could a water pump seal reseat itself that fully? Could it have been the thermostat gasket giving out from the movement when I overheated it and then when I brought it back to temp it moved again and sealed up? Seems like a stretch. Any ideas?
I guess I'll just run it until I can get it to leak again. I could pressure test but I'm almost sure it was coming from the engine side of the circuit so that doesn't help me much. Leakdown test maybe the next thing to do?

 

can't give a specific answer to this situation. all i can say is look for the dried up coolant. you should be using pink so look for a whitish pink powder. leakdown test is for blown head gaskets, or exhaust fumes in the coolant. i feel kinda meh towards leakdown tests since it only tests for 1 thing. i say do a compression test since that will tell you if there are other problems. if you get 145-150psi, you're golden.

i think you're worrying too much btw. you have a timing belt w/p kit. i say just do the kit, make double sure you're sealing everything properly, and go from there.

 

Thanks. Yeah that probably what I'll do more or less. I might run it long enough to see if the HG is going to blow immediately. I overheated it pretty bad. And I'm just curious how it would happen like that.

 

is your reservoir filled to the brim?

 

No it's about 2/3. Was empty after I boiled that sucker tho...

 

so it was empty before, filled after, and you didn't add any coolant to the reservoir, right? you might need a radiator cap. that could cause a lot of these symptoms. if the cap blew, it might've shot coolant everywhere in the engine bay and in to the reservoir.

 

I had a similar type issue in my 98 Mustang about 7 years ago. It ended up being the upper radiator hose had split on the bottom side of it and so it would only leak while under pressure after the thermostat had opened.

 

I’d do the kit, hoses, and clamps, thermostat, checking those things as you go. You may find the cause was a stuck thermostat etc. It overheated so hard to say what caused that now, a leak or something else. Could be a clog in the rad too, flush it well while you have it out and see what crap comes out.

 

You overheated you're engine VERY badly. If you didn't do damage to the head gasket or head, you should go play the lottery because luck is on your side. You can always buy a coolant system pressure tester and test the system for leaks.

 

The very badly comment is possible, if you drove it a long time overheated. If you did that, it would have taken a lot of coolant to refill it.

Good advice to do a pressure test, before and after the kit .

 

Last fall had an intermittent leak that I could not find...
turned out to be a split in radiator hose right at the hose clamp.

Hose was less than year old.....gates.
It would only leak after being on highway for more than half hour...
and then would become enough to spray pink.....

 

Yep... Figure I've got a 50/50 chance (or worse) that the HG blows pretty soon. That's part of why I would like to avoid doing the WP / timing belt if I don't need to. If the head's gonna blow in the next 500 miles I'd rather do it all at once instead of in two rounds... Luckily it was not hot for long, less than a mile I figure. But it did hit 270+ so that's plenty of heat to warp a head

 

I was starting to hope it really was just splashed coolant working its way down the engine but the leak started again today.
It's def not coming from any radiator hoses etc but it's really hard to tell exactly where the origin is.
Doesn't help that my front main is leaking oil so it's a bit of a mess. At some point I need to do the timing belt/ WP/ seals but it's not good timing for me so I'd love to put it off a little longer if I can trace the leak to something else.
The bypass tube that's famous for leaks is the rubber hose coming off the driver's side of the thermostat, right? It's not coming from there. But it also doesn't really seem to be coming from the water pump? At least it's not getting on the pulley or spraying around the bay at all it's just dripping straight down the face of the engine.
Can someone tell me where the weep hole is on the water pump housing?
It's possible that it's coming out of either the WP gasket or maybe the bottom of the thermostat housing gasket.
Def not coming from the rad hose.
Are there any other possible sources of a leak in the area of the water pump / thermostat housing?

Like I said it was dry as a bone while driving at temp on the highway for a while and then just started again this morning after going like 3 miles, no highway. So it's weirdly intermittent, only happens when at temp/pressure but not all the time.

Is there any point in a pressure test if it's on the engine side of the system? I did replace the rad cap because why not but I'm 100% sure it's not coming from the radiator or any of the hoses.


[/GALLERY]

 

Its the 2.7L 4bangers that are notorious for head gasket failures.....not these.....

 

the upper hose is connected to a water outlet thats bolted on the intake.
the intake gasket handles coolant at the upper hose.
these you can check by simply looking down in from the top of the engine behind that timing belt cover.

the water pump is right there.
yes the thermostat gasket on the water pump.
yes the extra hose but i think that's just for automatics. you got one?
these you have to take off the front covers to figure it all out.