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Old 09-27-2005, 02:38 PM   #1
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Default Pressure Check and Upper Intake Question

Hi all,

I知 taking my 95 Bonneville (NA Series II 3800) in for an oil change. Recently the car used a little coolant. Because of this forum, I知 well aware of the upper intake manifold problem. While the car is in for its oil change, I知 thinking of having a pressure check done on the cooling system. My question is the following. Will a pressure check reveal a failed upper intake manifold?

Thanks,
Leif W.
1995 Bonneville SLE (131,000 miles)
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Old 09-27-2005, 02:46 PM   #2
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Yes, A pressure test would show a drop in pressure w/o it being obvious where the coolant pressure was going.

Be careful after this..it could push coolant into your oil, and rupture the manifold if it wasn't already fully ruptured.
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Old 09-28-2005, 12:15 PM   #3
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Default 1998 Bonneville Coolant Problems

Hey,
I was reading stuff on the forum, trying to figure things out without bugging everyone with a question, but I'm not enough of a car person, so here goes:

Around 58k miles (10/2003), the upper intake manifold went. I was cruising down the highway and the tranny downshifted so I could pass a truck, and after it upshifted, the car started going nuts, shaking violently (still running). I stopped like a mile or so at the next exit, and then it stalled. The annoying part was that I was on a trip, so I towed it to the closest dealer in the direction of home and they replaced the upper intake manifold, starter, and did a tune up and oil change. I thought that everyone would be fine down the road and for a while it was (for the most part - there was a strange shuddering at one point that seems to be better but I want to stay on the manifolds). At ~73k miles (8/04), the fuel regulator was replaced (recall). The recall notice mentioned some intake manifold, but I never understood why.

So lately I've noticed the car is eating coolant. I brought it to the dealer and they did a pressure check, and that was fine. They also did something called a hydrocarbon test, and they said the level was a little elevated, but not enough to condemn the head gaskets. So my question is this: What the heck could be wrong? I've seen stuff on these forums about kits and plenums and I'm more than a little confused now. If they didn't replace the lower intake, could that be about to fail? Given when my upper failed, could it happen again? I don't want to have to keep bringing this thing to the dealer ( I don't have enough experience to work on this stuff myself - I'm limited to oil changes and tune ups). Could the coolant simply be evaporating? It seems to move from full warm to full cold in about 750 miles or something like that. Maybe about 1-1.5 months. Any thoughts would be great, and also any advice about which prevention steps haven't been taken based on the 1 or 2 things that the dealer did to the upper intake would be helpful. Thanks!!
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Old 09-28-2005, 12:26 PM   #4
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Sounds very much like your lower intake gaskets are leaking.
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Old 09-28-2005, 07:11 PM   #5
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You guys should check two things. 1. Your oil dipstick. If it has milky mud type gunk on it, there'* coolant in your oil. 2. Look at the coolant elbo that comes out of the lower intake manifold and makes a 90 degree turn into the tensioner/alt bracket. That little plastic peice has broken twice on me now. It will leak the most on a cold engine that just started up. (waterpump working but thermostat closed)
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