Coolant Leaking From Intake Manifold - Nissan Frontier Forum
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#1 (permalink) Old 07-07-2009, 07:44 AM
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Question Coolant Leaking From Intake Manifold

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!

2000 Frontier Crew Cab, 4x4, Automatic

Last edited by SAH; 07-07-2009 at 07:46 AM.
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#2 (permalink) Old 07-07-2009, 11:23 AM
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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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#3 (permalink) Old 07-07-2009, 11:48 AM
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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.

2000 Frontier Crew Cab, 4x4, Automatic
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#4 (permalink) Old 07-07-2009, 12:11 PM
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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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#5 (permalink) Old 07-08-2009, 10:14 PM
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What Joe said.

Run it 'till it breaks and fix it faster!
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#6 (permalink) Old 07-09-2009, 06:05 AM
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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.

2000 Frontier Crew Cab, 4x4, Automatic
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#7 (permalink) Old 07-09-2009, 06:47 PM
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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.

Run it 'till it breaks and fix it faster!
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#8 (permalink) Old 07-09-2009, 07:15 PM
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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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#9 (permalink) Old 07-13-2009, 07:14 AM
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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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2000 Frontier Crew Cab, 4x4, Automatic

Last edited by SAH; 07-13-2009 at 10:11 AM.
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#10 (permalink) Old 03-07-2010, 11:35 AM
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Many thanks for posting the info and, especially, the pics!

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