Hi everyone-

I’ve searched this forum and others but am having trouble finding any threads that mirror my coolant issue.

1999 SR5 4WD. If the car is being driven daily, I don’t see any coolant leaks. However, it sat all week when I was out of town and there was a decent size puddle of coolant under the car when I got home today. It seemed to be mostly near the rear of the engine so I followed the leak up and noticed there was quite a bit of coolant in the valley between the valve cover and intake - mostly on the driver side. I took off the upper/lower plenum and throttle body to get a better look. None of the hoses were leaking and there was no leak at the block inlet (front) or outlet (firewall). I dried up the coolant in the valley and figured I’d pressure test the system tomorrow. I mowed the grass and as I was putting the mower away, I glanced in the engine bay and there was more coolant in the valley. The engine was never started and hasn’t in over a week. How is coolant seeping into the valley with the car off!?!???

Any ideas?

A few weeks ago I did the valve cover gaskets and had everything apart. This seems to have started at that time or else I never noticed it before because the car never sat for days without being driven.

The only thing you would have disturbed during the VC gasket repair are the 2 coolant lines going in and out of the IAC on the throttle body. The only other coolant flow across the area you're seeing coolant accumulation is pipe labeled 16268. I highly doubt it would be leaking there though as that is a steel pipe.

TOYOTA 4RUNNERVZN185L-GKMGKA - TOOL-ENGINE-FUEL - RADIATOR WATER OUTLET | Japan Parts EU

Thanks. The lines going into/out of the throttle body are dry. Those sit over the valley on the passenger side and I’m seeing coolant on driver side so I don’t think it’s those.

The coolant is magically re appearing on the driver side towards the front. I’ve got the intake plenums off now so I can see it pretty well. How is coolant seeping Into this spot with the engine off (and cold) and no pressurization of the cooling system??

I agree with @JRZEE2000TR4LTD it's unlikely 1626862060
PIPE, WATER BY-PASS, NO.1 would just start leaking but it sounds like it is based on your description to me.

somehow? during your work maybe you put pressure on the water by-pass and maybe something was lose enough to cause that to leak?

that connection uses FIP gasket material. it does wear out and it will leak at some point.

we all had a nice chat this very part a while back in this thread. helpful pics included in this thread.
water by-pass o-ring part number?

it could be your lower intake as well but why it would just start leaking a ton like that all of a sudden? but that said anytime you mess with anything mechanical it can upset the balance and cause other issues.

update us when you figure it out. I'm thinking it will be obvious once you find it. I'm curious to know what happened?

thanks

Thanks. I’m wondering if the area under my intake manifold is just a lake of coolant at this point and the water bypass tube is leaking and filling up the space under the manifold. Prior to doing the valve covers, I replaced the heater core and as part of that process I flushed the system 2x with distillled water, then 2x with 50/50 Toyota red and then filled again. The PO had used green and I wanted all that out. Maybe during that process I dislodged some sludge that was sealing a leak?

Should I plan to replace the bypass pipe or just reseal it?

The more I look at pics in the link you posted, the more I think I have a leak under the intake manifold, which is then seeping out through that intake manifold gasket and pooling in the valley. Sounds like I’m going to need to pull the intake manifold to diagnose but thankfully I can leave the valve covers on.

If you have a bad intake manifold gasket I can see it happening.


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the bypass pipe should be fine unless it's rusted and compromised. I did a new one and re-used one at one point. just depends on how much cleaning you want to do? it's kind of hard spot to get at and it's not much fun to re-seal it. just make sure your ready and do a practice run without the FIP just to make sure you have the process down. once the FIP is on it's go time and you want it to go smooth. you will see what I mean if you decide to re-seal it. it's fiddly to get it into that spot.

one other thing... if your going to go down that far and take the lower intake off. you might as well replace the knock sensor wire harness. it get really brittle after 20 years and if you don't replace it while you have the lower intake off your at risk of messing it up and then having to re-do everything you just did.

Toyota 5VZ-FE/3.4L OEM Knock Sensor Wire 82219-34010

I have tried feld pro gaskets and I had bad luck with them on the lower intake one time. I only do OEM toyota gaskets now for lower intake. worth it IMO. feld pro are good and I know some people swear by them but they are not OEM quality.

I'm not saying you have to do it but... it's a really really good idea.

Added to the list for when I do my fuel injectors (already did VCGs)

When you buy a top end gasket kit from YotaTech that harness comes with. Both engines I did the head gaskets on the connector clips shattered removing the old harness from the knock sensors.


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Any update on this

Not yet. The problem seems intermittent but there is definitely fresh coolant in the valley (only on the driver side) whenever I drive the car and the level in the overflow reservoir slowly drops over time.

This may be totally crazy, but my theory is that the bypass pipe is leaking, filling up the chamber where the knock sensors are, and it’s seeping past the intake gasket and out into the valley. From there, it drips out the back of the valley and onto the ground. I’m just speculating because I don’t know how else fresh coolant is showing up in the driver side valley. If it were the hoses under the TB, the coolant would be in the passenger side valley, but that side is totally dry.

I’ve ordered the water bypass pipe, FIPG, knock sensor harness, and intake gaskets and plan to dive in and do it in the next few weeks.

There is a rubber gasket on the IAC, did you mess with that when you did your valve covers? That little gasket is easy to fall off or get pinched if you're not careful when reinstalling the IAC.

If it's still uncertain you could always get a $20 dye test kit.

Good deal keep us posted I am curious

Sometimes the 1" hose that connects to the bypass pipe at the rear of the engine leaks and the coolant flows down the pipe into the valley. My leak was from the one of the two intake manifold-to-cyl head gaskets that were installed by the stealership when they did my cyl head gaskets about 10 yrs previously.