Hey Guys

Sorry for not using my first post here as an introduction but i have some very serious problems with my car which do require immediate attention.

Car:
LEXUS RX 3,00 / 2003 V6

Starting Point:
Problems started with a very slight midfire on cold starts.
As the months flew by it got worse and worse and in addition the exhaust started emmiting thick white puffs of smoke.

I pinpointed the misfiring cylinder to the #5 (the middle one on the foremost bank).
Starting with the simplest things first I pulled the corresponding plug and it was SOAKING wet with coolant.

Tests that followed:
Oil in coolant - negative
Coolant in oil - negative
Bubbles in the Radiator - negative
Nice even compression on all 6 cylinders

So after removing the plastic intake manifold because i wanted to find some evidence the following has been discovered:

On the aluminium intake plenum the number #5 runner is covered with a thick creepy goo of coolant and oil - so are the valves. Every other runner is clean as polished.
The whole plastic intake manifold is covered completely with this milkshake.

I believe coolant is running into the #5 cylinder because it is the bottommost runner on the intake manifold.

Where the **** is it coming from?

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Please Lexus experts help me with your knowledge
And sorry for any typos because english is not my native language!

Thanks Thanks Thanks!

Probably a blown head gasket. A leak-down test will verify for sure but you have all the symptoms.

Why not an intake manifold leak?

This is the most likely situation, based on the data provided. If the leak was in the chamber (head gasket), then the compression would push its way into the coolant circuit as well as gasses will work their way into coolant on power stroke. I am with carguy07 as the coolant is being sucked in on the intake side.

Was any work done recently? Or low quality parts used some time back.

Salim

Thanks for all the answers so far.

I would love to provide you with background service information, but i can't,

It's a second hand car and I am absolutely clueless what the owner did try on the engine itself.

What are the possible causes for coolant beeing sucked into the intake on this on this particular engine?
I would love to check them!

As far as I can tell, there are only two coolant lines going into the throttle body itself and a bunch of vacuum lines to the plastic manifold. Or did I miss something and vaccum lines were mistaken with coolant or smth.?
Or some kind of gasket I dont know of?

Also the water passages on the aluminium intake plenum are so far away from the middle cylinder that this can be ruled out too - at least from my perspective.

I know some manufacturers route coolant through the intake or even throttle body and EGR valve, etc. This must be a Japaneses design thing since I've seen it in Mazda and Subaru not in any German cars. Anyway, it could very well be the intake if RX routes coolant through that area.
As for compression test and the head gasket, depending on the location of the break in the gasket, compression results may or may not be affected. The best test for isolating a faulty head gasket is the cylinder leak down test. It will tell you which section of the gasket has been compromised.

I had a leak exactly like that, turned out to be the intake manifold gasket. I would pull intake and replace the gasket.

Where does coolant flow in the intake manifold? I can see where a bad intake manifold gasket could cause an air leak and a subsequent lean condition but I don't understand how it could cause coolant to get into a combustion chamber.

If you want photo evidence, dig the knock sensor DIY. You will see that the pictures of coolant and air channels.

Hot coolant is circulated in the throttle body to prevent freezing of the fuel vapors.

Salim

I've seen a modification even on Solaraguy where people did a bypass for the coolant hose that runs through the throttle body (right by the throttle butterflies) just to improve performance (don't recommend anyone doing this unless you really know what you are doing).

The throttle body sits at the upstream end of the intake manifold and yes, it does have coolant passages in it to prevent freeze-up of the throttle body but I don't see any path for that coolant to get to just one cylinder in the block.There are no passages in the intake manifold for coolant to leak into the head, it just divides the air from the throttle body equally amongst the 6 cylinders intake valves. It only passes air. I suppose it would be possible for coolant to leak into the throttle body but then it would show up at all 6 cylinders not just #5 cylinder and would likely be completely consumed in the combustion process just like moisture entering the induction system would be.

This is why I think it is a head gasket leak, not an intake manifold leak.

Also, I just finished a head gasket replacement on a 4AGE engine that had the same symptoms as the original poster listed. ie. no oil in coolant, no coolant in oil, no bubbles in radiator, even compression on all cylinders. Leak-down test pointed to #4 cylinder leaking into water jacket and pulling the head confirmed it. Just my experience.

A leak down test can eliminate/confirm the intake side problem.

Salim