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Old 05-23-2020, 03:38 PM   #1
amgarb
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Default SOHC, coolant leak @ intake manifold?

2001 SC1. 291xxx miles on the car but unknown mileage on 2nd engine. Bought it 6 months ago so son could learn to drive a stick shift.

Son came home and car was smoking due to coolant leak. Green antifreeze running down back of engine and dripping on exhaust. Crawled underneath and found it running down where transmission attaches to engine. Went topside and pulled air intake tube. Using a mirror, it seems to be leaking from where the intake manifold attaches to the head; near the rightmost (driver side) bolt.

I'm thinking it is the intake manifold gasket. I ripped the attached image from Alldata (using my library's subscription!) and marked in orange where it appears to be leaking. Is there any cooling running through the intake in this area? What are the odds that it is actually a head or head gasket problem?

Also tried to get a picture with inspection mirror. Hopefully it makes sense.
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File Type: jpg intake2.jpg (98.4 KB, 23 views)
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Old 05-23-2020, 03:50 PM   #2
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Default Re: SOHC, coolant leak @ intake manifold?

Is that intake manifold plastic? If so, there is coolant going into/through it via a small metal tube. I'm not familiar with those "new" gen3s, but my understanding is it is a common point for leaks. There are quite few threads here regarding the problem and there are aftermarket repair kits specifically for that job. It is not likely to be either the head gasket or manifold gasket.
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Old 05-23-2020, 03:56 PM   #3
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Default Re: SOHC, coolant leak @ intake manifold?

Sorry, should have mentioned that my intake manifold is not plastic.

I got confused when searching the archives. It almost seemed like most of the intake gasket issues were on the plastic manifolds or on the DOHC engines.
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Old 05-23-2020, 04:06 PM   #4
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Default Re: SOHC, coolant leak @ intake manifold?

Is there coolant running through the throttle body?
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Old 05-23-2020, 04:25 PM   #5
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Default Re: SOHC, coolant leak @ intake manifold?

Quote:
Originally Posted by 454cid View Post
Is there coolant running through the throttle body?
Thanks for the response.

It does appear there is a heater hose running from the throttle body to the firewall. This hose is dry. Picture attached.

Maybe I'm just dense... not sure I understand the intent behind the question.
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Old 05-23-2020, 05:15 PM   #6
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Default Re: SOHC, coolant leak @ intake manifold?

It's a sohc so it's a metal intake. Most likely the intake gasket is leaking there as there is a coolant passage there I believe. Try pressure testing the cooling system to see if it leaks, if you don't have one see if a parts store will allow you to rent one. That's close to the head surface too so it's hard to rule out a head gasket.
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Old 05-23-2020, 05:26 PM   #7
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Default Re: SOHC, coolant leak @ intake manifold?

I've rented a pressure tester from Auto Zone before when I was trying to diagnose my 99 DOHC. That one is parked in my barn waiting for me to get motivation to pull the head.

I'm not sure how much help the tester will be though. When I start the car I can use my inspection mirror and see it dribbling out right where I marked in my first post. At this point, I'm thinking I may just need to pull the intake.
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Old 05-23-2020, 05:35 PM   #8
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Default Re: SOHC, coolant leak @ intake manifold?

While it could be the intake manifold gasket, the normal 3rd gen problem with that is a vacuum leak and uncontrolled idle speed.

I would guess that the leak is actually at the screwed in nipple from the intake manifold to the heater core.
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Old 05-23-2020, 06:30 PM   #9
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Default Re: SOHC, coolant leak @ intake manifold?

Quote:
Originally Posted by fetchitfido View Post
While it could be the intake manifold gasket, the normal 3rd gen problem with that is a vacuum leak and uncontrolled idle speed.

I would guess that the leak is actually at the screwed in nipple from the intake manifold to the heater core.
Can you describe where this problematic nipple is? I have a picture in post 5 of this thread showing the hose running to the heater core but it is completely dry.
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Old 05-23-2020, 06:46 PM   #10
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Default Re: SOHC, coolant leak @ intake manifold?



This. If it's coming out at the threaded part, depending on how pressurized it is when it leaks, it'll just flow right down the runner right to your suspect bolt head.

It may still be the intake manifold gasket as they're old enough the "normal" failures should have been fixed and it's time for normal "the car is old as dirt" failures to occur
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Old 05-23-2020, 07:03 PM   #11
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Default Re: SOHC, coolant leak @ intake manifold?

That picture helps a lot. I can see how it would flow down and around to the area I identified.

How difficult to replace that nipple? Thread it out with a pair of vise grips?

Or is the typical failure mode a crack in the casting where the nipple threads in?
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Old 05-23-2020, 07:28 PM   #12
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Default Re: SOHC, coolant leak @ intake manifold?

So I went out and started it up. Was able to see the nipple with inspection mirror. Dry all around. Let it run for a few minutes. Wiped finger on bottom of runner and it is still dry. Meanwhile, antifreeze is dripping from where intake mates to the head.

So I'm pretty convinced it is not at the nipple. Although I wish it was as it appears easier to replace. I think I'm going to pull the intake and take a look.
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Old 05-23-2020, 09:13 PM   #13
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Default Re: SOHC, coolant leak @ intake manifold?

Quote:
Originally Posted by amgarb View Post
Thanks for the response.

It does appear there is a heater hose running from the throttle body to the firewall. This hose is dry. Picture attached.

Maybe I'm just dense... not sure I understand the intent behind the question.
You were asking about coolant in the intake, and I'm not sure of that answer, but I've heard of throttle bodies having coolant running through them. The Vortec 350 does and some/all of the earlier TBI V8's do as well. I was thinking a leak there someplace could be the source of what you're seeing. It's so common for leak oil or coolant to travel and seemingly take invisible paths.
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Old 05-23-2020, 09:41 PM   #14
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Default Re: SOHC, coolant leak @ intake manifold?

Quote:
Originally Posted by 454cid View Post
You were asking about coolant in the intake, and I'm not sure of that answer, but I've heard of throttle bodies having coolant running through them.
I see. I thought you may have been pointing me towards a known problem area by asking a question.

I've been researching and looking at parts. Attached is a gasket image from rockauto. I'm thinking the lowermost rectangular hole may be a coolant passage. My leak appears to be around this area.
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Old 05-23-2020, 10:27 PM   #15
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Default Re: SOHC, coolant leak @ intake manifold?

Quote:
Originally Posted by amgarb View Post

I've been researching and looking at parts. Attached is a gasket image from rockauto. I'm thinking the lowermost rectangular hole may be a coolant passage. My leak appears to be around this area.
You may be correct. Unless maybe it's EGR? Where is your EGR valve?
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Old 05-23-2020, 10:36 PM   #16
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Default Re: SOHC, coolant leak @ intake manifold?

Pretty sure the leftmost hole in my gasket image is for the EGR.
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Old 05-24-2020, 12:13 AM   #17
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Default Re: SOHC, coolant leak @ intake manifold?

The S-Series doesn't use a heated TB so no coolant lines there.
The EGR valve is on the head, not the intake manifold though there is at least one passage through the IM that the EGR valve utilizes.

I believe the left most hole is the coolant passage while the lowest hole (under cyl 4 intake hole) is the EGR passage.
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Old 05-24-2020, 01:49 AM   #18
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Default Re: SOHC, coolant leak @ intake manifold?

Quote:
Originally Posted by fetchitfido View Post
The S-Series doesn't use a heated TB so no coolant lines there.
The EGR valve is on the head, not the intake manifold though there is at least one passage through the IM that the EGR valve utilizes.
I know my DOHC EGR is on the head, but I wasn't sure about the SOHC or if that may have changed with the generations.
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Old 05-24-2020, 10:25 PM   #19
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Default Re: SOHC, coolant leak @ intake manifold?

Got it fixed today. It was the intake gasket. You can see in my attached photo that the gasket looked shiny and was a bit thinner directly below the water passage.

The old gasket was a Felpro. I put a Felpro back on.

The EGR passage is definitely the hole clear on the left in my photo.
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Old 05-25-2020, 01:22 AM   #20
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Default Re: SOHC, coolant leak @ intake manifold?

Quote:
Originally Posted by amgarb View Post
Got it fixed today. It was the intake gasket. You can see in my attached photo that the gasket looked shiny and was a bit thinner directly below the water passage.

The old gasket was a Felpro. I put a Felpro back on.

The EGR passage is definitely the hole clear on the left in my photo.
I'm glad you got it fixed. I wonder what caused it.
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