Help finding the source of a coolant leak

What would I compression test? I can't pressurize the coolant because everything is apart, and it's an external leak so a cylinder pressure test isn't what I'm concerned with.

 

Ah you kept saying head gasket so I thought you were thinking combustion pressure pushing out coolant through the hg or a crack in the cylinder at the hg.

You think the gasket is leaking only at the coolant passage and not getting pressurized by a leaking cylinder?

Sounds rare. I haven't heard of a hg failure at a coolant passage on a 5vz.

 

Yeah, no bubbles or any issues with combustion pressure getting into the coolant. Just an external leak.

It is rare, I found only 2-3 instances online and they were all high mileage engines.

I'll just roll the dice and put it back together hoping it was only the intake.

Thank you so much for the help!!

 

When she goes back together I highly recommend this https://www.kseal.com/

In addition I would check the torque on the head bolts too. Set your torque wrench to the setting and see if it “breaks” first or the bolts turn.

 

I've used k seal with good results before.

Never heard of a head bolt coming loose. Is that a thing with this engine?

 

No, it is just something else to check and eliminate.

 

Following up on this...

After further inspection and cleaning, I am 99% sure this leak is isolated to the intake manifold gasket leaking at the passenger side front coolant passage. I found heavy corrosion on the gasket itself, and some pitting on both the head and manifold. The gasket is a 3-layer type with paper on both sides of a metal core with bonded rubber gasket built-in.

I cleaned up the surfaces with a razor blade to scrape any high spots off, then red and grey scotch brite to polish it up, it's looking pretty good.

Interestingly enough, I changed the coolant in this truck at 50k miles and again at 100k miles when I did the timing belt and water pump. Both times using Toyota red coolant 50/50 with distilled water. Despite that, there was noticeable corrosion and deposits, so I don't think a strict maintenance schedule would have done anything to prevent this.


During reassembly, I am questioning the design which uses angled intake surfaces. As you tighten the bolts, it pulls the gasket at an angle as it pulls the intake into the vee. This causes the gasket to shear slightly as it takes a seat. based on this I would suggest a small amount of grease or silicone sealant on the coolant passage surfaces to ensure they can slide easily without damaging the bonded rubber parts.

 

This isn't the only engine to see this on. (The intake leak, not so much a design prob.) I accidently found the same thing on my old Sienna. Any time there's an unexplained loss of coolant this is suspect as coolant doesn't evaporate. I never use silicone on rubber, ymmv.

 

Good observation on the angled head intake surface. Lots of modern engines are now flat where the intake/head meet. In the old days when you would surface the intake on older v-8’s to remove defects the “V” actually gets wider and it can cause some intake alignment issues. Yet one more thing to worry about on reassembly.

 

Hylomar is made for these applications.....

just dont use it on the multi layer metal gaskets...

$26 Hylomar Universal Blue Non-Setting Sealant Silicone Jointing Compound 3.5oz

Hylomar Universal Blue Non-Setting Sealant Silicone Jointing Compound 3.5oz: Amazon.com: Industrial & Scientific

 

Interesting, I think I've heard of that stuff.

The only thing I've used on MLS gaskets is Permatex copper spray.

I've run the truck up to a couple of heat cycles now - no coolant loss and no leaks.

 

I am thinking of doing this coolant bypass pipe resealing while I'm in the area soon.

I assume I would need to drain the coolant? If so I might avoid it and let it ride.

Also what's the torque spec on those pipe fittings? Probably 13 ftlb if they're 12mm? I can't find that pipe in a diagram or the FSM.

 

I drained the coolant by opening the radiator cap and unscrewing the drain at the bottom of the radiator into a bucket. It couldn't get any easier, just takes a while.

They are tiny little bolts. I forget the torque spec but 13 sounds high. You don't want to break one of them bolts off.