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Discussion Starter #1 (Edited)
I just got through replacing the knock sensor on my 2000 VG33e and after I put everything back together and filled the radiator, coolant started leaking from the intake manifold. The coolant is coming out of the throttle body opening and there's a stream coming down between the engine and transmission. It leaks about 1 cup a minute. I took pictures before I did the job and everything seems to be hooked up right. Somewhere coolant is dumping directly into the intake manifold and what doesn't go into the manifold drips down onto the engine. This is not a throttle body leak. Any help would really be appreciated otherwise I'm going to have to take off the upper manifold again to try and find the problem and that's a real PITA! :(
 

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I have no clue why you are now leaking coolant but I will give you a free bump so others may read this and give you some input.

I just don't understand why it is now leaking. I assume you didn't have to touch any coolant lines to remove the the manifold. Well, actually are the coolant lines routed thru the TB to help heat it up during start-up? Are those lines properly connected or did you lose one?
 

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Discussion Starter #3
Well I've been thinking what might have gone wrong and one scenario that accounts for everything I've seen is that the lower intake manifold cracked during installation allowing coolant to flow from the water passage into the intake passage and onto the engine. I did follow the manual for the proper 3 step torque sequence and bolt pattern. I've got a question out for a Nissan tech at justanswer.com but if the tech doesn't come up with a solution I guess I'll have to tear everything back down again to see what the exact problem is.
:sickly:
 

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I think you are going to have to tear it down and replace the hoses or tighten a clamp.

As you know the underside of the intake is an octupus of tubes running everywhere.

I think the tubes carry the coolant and not a cracked manifold. I'd check all tubes.
 

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Discussion Starter #6
I just remembered that I used an intake manifold gasket set with neoprene inserts that fell out real easily and had to be positioned with great care. The gaskets are ROL gaskets from RockAuto. If the insert moved or tore then that would allow coolant to move into the intake passage and out of the throttle body opening as the level rose and also leak onto the engine. I'll find out when I tear everything down again this weekend. This time around I've already got genuine Nissan gaskets from the dealer. It seems more likely to be the gasket than a cracked manifold since I did follow the factory manual's procedure for removing, installing and torquing the manifold.

Hopefully this time around I can do the job in a lot less time. I did see JoeFrontier2's knock sensor relocation writeup but decided to go the hard route and do the actual knock sensor replacement and believe me, it really is the hard route. Well maybe if I ever get a supercharged truck I'll be able to do the job real quick since the supercharger requires that the knock sensor be replaced and not relocated.
 

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Sounds like you're on it. Bummer to tear down, again.
While I was in there I'd check where the gooseneck connects to the block. Mine gave it up, and beleive me, you don't want to go there from scratch. Pull it and reseal. You can't see the rust that forms w/o pulling it. Might need to have a new bypass hose on hand. Hard to get it off in one piece. Pain w/the sc anyway.
I'm gonna have to get on that knock sensor one day. :)
 

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Search around on here man... There is a wax thermostat seal that has to do with your cold start and idle mixes. They go bad..... They also leak around the same areas you are saying... Mine leaks but its a hose just under the TB that has a bad clamp... I really dont want to take my manifold off very bad..... When it starts doing more than a drip drip... Ill fix it. Until then I leave my cabin air set to recirculate so I dont have to smell the burning coolant.... (it only leaks 1cup or less every 10+k miles..)
 

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Discussion Starter #9 (Edited)
Well, it was as I suspected and hoped, the gasket inserts slipped during the install even though I was super careful with the placement and thankfully the manifold was not cracked. At first I thought that the manifold had cracked but then I remembered I had removed and installed/torqued the manifold according to the factory manual so I didn't think that was the problem. A good thing too since I looked at the price of a replacement lower intake manifold and it was over $350 at a discount Nissan parts dealer (BuyNissanParts.com). When I pulled the lower intake manifold one of the inserts was torn and the intake manifold was full of coolant on the cylinders where the intake valve was closed.

I had used ROL gaskets from RockAuto. A mechanic friend of mine told me that the more modern gaskets use neoprene O ring type inserts so I went with that style of gasket on the lower intake manifold. The original factory gaskets are thin sheet metal with some type of material around the ports. At RockAuto there was choice between ROL and FelPro gaskets but the ROL gaskets also came with a complete set of injector O rings so I went with ROL. When I got the ROL gaskets the inserts fell out easily and I considered gluing them in with RTV but then I decided not to because there were no instructions telling me to glue them in and I thought that if I glued them in with RTV that might cause problems if the inserts couldn't shift during torque down. Incidentally, the FelPro gaskets also looked to be the insert type but I don't know how securely they were attached to the metal carrier.

I must have checked the alignment of the gaskets a half dozen times but that wasn't enough as evidenced by the torn insert. I ended up using Nissan gaskets from the dealer and that solved the problem. Before starting the engine I removed the spark plugs from the cylinders that had open intake valves and hand turned the crank to ensure I didn't have hydro lock. I then drained the oil and changed the filter. Over 5 quarts of fluid came out of the crankcase so there was over a quart of coolant in the crankcase. Afterwards I scanned the engine and no P0325 code but it's kind of interesting that the old knock sensor read 560 KOhms resistance, within factory specs. So, if you want to waste two long weekends and become an expert at removing the upper intake manifold then go ahead and use ROL gaskets.

Some notes:
The two small heater hoses at the back of the manifold are a real pain.

There are two electrical connections at the back of the upper intake manifold, one of them is UNDERNEATH the manifold, one at the back.

There is a small bolt attaching the front timing belt cover to the coolant neck on the lower intake manifold.

Paying a mechanic to do this job is money well spent!

Incidentally, if you got a pair and decide to replace the knock sensor yourself you might also want to change the pre cat O2 sensors and valve cover gaskets since you have easy access to those components. I did since I have over 102,000 miles on the odometer. I got Denso O2 sensors from RockAuto and at first I thought that they sent me the wrong parts because the threads were way too small but when I checked with the parts guy at BuyNissanParts.com he told me that the O2 sensors screw into a larger adapter nut so I just unscrewed the adapter nut from the old O2 sensor and put it on the new sensor. I included some pics of the crappy ROL gaskets with the Nissan gaskets and a shot of the underside of the intake manifold that JoeFrontier2 was referring to. There's a shot of the lower intake manifold with a couple of the runners full of coolant. The runners that didn't have any coolant in them must have drained into the cylinders hence the 5+ quarts of fluid in the crankcase.
 

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SlyJhereg, I am doing this work for a second time on my truck. The tools I used are as follows, for the straight hose which is the more difficult due to the angle and position of the screw clamps. I used a 1/4" socket and drive and as mentioned replaced the squeeze clamps with screw clamps. For the elbow hose I used a standard flat tip screwdriver as you can angle the clamps to make them accesavle once the wire harness and such are removed. I will post some pics and a write up in the next few weeks on replacing the knock sensor.

I do have a question for SAH when replacing the intake manifold gaskets during your repair, did you replace the head gaskets as well? The service manual says to replace the head gaskets if you are using a new intake manifold gasket set. I can only assume this is due to the tighting sequence that you have to go through to ensure the plenum lines up with the heads. I had a coolant leak between the plenum and the 1 head on my truck a year ago and immediately did the repair, I initially used the factory original intake gaskets from the dealer. I also added some extra protection and used an extremely thin coating of red rtv around the coolant ports on the heads to provide a better seal. I had absolutely no problems for exactly 1 year and now I have coolant leaking into the cylinders internally and causing a misfire. I have torn the intake down for the second time and have decided to intall the FelPro intake gasket set as they are a little thicker and have a silicone outer skin on them. I am seriously thinking that not being able to align the heads with the intake manifold and gasket in place is causing more trouble for my situation. I also can not loosen the head bolts and do the sequence as this more than likely destroy the sealing capabilities of the head gaskets.
Sorry for the long winded text but if SAH has a minute to please reply with the information requested and let me know if you have had any subsequent leaks I would appreciate it. Also if any of you guys have any ideas on how to align the intake and heads without replacing the head gaskets let me know.

TIA
 

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I am about to replace the intake manifold gaskets. Coolant has been leaking from underneath the intake and gets inside the piston. Also, occasionally I see coolant on the ground under the front passenger side of the engine. I am not sure how it gets inside the piston. Suspect that it is either through the intake or though the spark plugs. Car smokes white cloud from the exhaust for 10 minutes after start. No coolant in oil or vice versa. Based on what I read, it seems that either a coolant line needs to be replaced under the intake or the lower intake gasket is bad. T-stat and gooseneck pipe look clean. Any advise? Should I do a pressure test before I tear down the intake? Is it possible for coolant to enter the intake manifold?
 
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