Well I'm in need of some mechanical advice on our Chevy Venture.

Long story short. Last weekend I replaced the intake gaskets on it. It has the famous 3.4L notorious for intake gaskets and head gaskets. Let me say the project didn't go as smooth as planned but I got it done.

Somewhere along the way I have developed an oil leak! My guess is the back valve cover gasket slipped out when putting on. So gotta fix it again.

Now to my real question, before doing all this I had white smoke only on warm-up/cold-start, hard starting, lose of coolant with no leak, and a heavy coolant smell outside the vehicle after running. Also until the thing was well warmed up you couldn't take off, it would pretty much stall out. My oil was clean, and no bubbles or gas smell in the radiator or overflow, so I was pretty sure was the intake.
Now I'm still getting a rough idle on warm-up (open-loop). as well as extreme hesitations. What gives, I'm about to give in and take it somewhere, but I'm gonna get really ticked off when it's something so simple and stupid.

I have changed, a few other parts while I had it apart and a few weeks ago I changed the plugs and wires. I've checked all the vacuum lines, connections everything seems in order.
Any ideas? give me a list, I'll check it or tell you if I've already done it. Thanks in advance for any help provided.

-Earle

 

Looks like I'm not the only one driving a minivan on this forum. Haha.
Have you done a compression test and a cylinder leak down test? These will confirm a blown head gasket. You could have a cracked or warped head and those type issues. Also do a pressure test on the coolant system. If it doesn't hold pressure you still haves leak. I'd check the old school stuff before I start checking sensors and computer issues.

 

yes, dude have to have a mini-van.

Have not done the compression test, due to the placement of the motor it's not easy, so I've refrained. I guess I should have done it when I had it all apart last week.

I haven't done a pressure test on the coolant system in a year, so I can go rent it and try that again.

I know why your requesting the compression test, but what do you think could be the issue with the cooling system, what I mean is what issue am I looking for?

Thanks for the reply, I'll get on this tomorrow, so much for a 3-day weekend. lol

 

In your first post I think I read that you are losing coolant but don't know where from and that you have a heavy coolant smell from the front of the van. If you have a head gasket/sealing issue you would smell coolant at the tailpipe. Smelling it at the front would indicate to me another leak. Possibly cracked head or block on the worst case scenerio or a loose hose clamp, split hose, bad water pump on the best case side of it. Could also be a heat bypass valve or radiator issue. Pressurizing the system without the heat and movement of the engine may help you pinpoint and external leak. The compression test and cylinder leak down test will help pinpoint a bad head gasket, block or head mating issue, and also check the condition of the valves and the rings. I think it is best to rule out the basic integrity of the engine before moving onto other things.

I've got three mini vans. A 95 and 06 Chrysler Town & Country Limiteds that help shuttle the kids around. Then at work I have a 99 Cushman White mini minivan as a service truck. I drive my Woody wagon on occasion just so I remember what a car is. Lol.

 

My experience is that white smoke is coolant as a result of a faulty head gasket. Now, you said you replaced the head gaskets. During this process, did you check that the decking surface of the heads was still flat and not warped? If it was warped and you did not get the head professionally machined, this could be the source of your current problems.

BTW - The intake/head gasket issue in the 3400 goes back to the earlier design, the 3100 (same block, same basic motor, I believe released in '94).

 

I must have mislead you. I only changed the upper and lower intake gaskets. Sorry for the confusion. Along with the cooling system test, and compression test I'm also going to test the EGR valve/system, that could be the source of bad idle, and hesitation.

I haven't smelled coolant yet...since changing the intake gaskets, and I replaced a few hoses that broke/looked questionable during that process. The white smoke I did have was only on idle, during a cold start or maybe after sitting for 30mins or more. I just figured with the way those intakes are designed that the water getting into the cylinder and pooling?

Thanks to everyone that has replied, I've got some testing to do, I'll update when I get those done. In the mean time if you guys think of anything else, please don't hesitate to reply!

-Earle

 

No worries, I may have also mis-read. But you are getting white smoke after the car sits and a cold start.

In all the cases I have known of blown LIM gaskets on 3100/3400 this smoke was NEVER s symptom. The coolant either goes out of the engine all together OR gets directly in the oil.

I've known a couple to have blown head gaskets and they had various symptoms. For instance, my '94 Grand Am with a 3100 began having a rough idle from a cold start and I never worried, it was a high miles engine and the rough idle went to 100% perfect by the time I got to the first stop sign.
About 6-12 months later, the next symptom was my temp gauge PEGGED! I changed the T-stat thinking it was old and sticking. I did a radiator compression test, no problems. I began finding when the gauge pegged, I could pull over, open the bleed valve, release some air and the rest of my travel the temp was fine. On the Grand Am, your radiator cap is on the overflow bottle (the radiator itself is a cap-less design). I began noticing loss of coolant, if I would top off before going to work, I'd get to work, open the hood and coolant was flowing out of the radiator cap. Replaced the cap (thinking it was no longer holding pressure), no change. Right before I had a friend of mine diagnose it, that week I was finally getting the big tell-tail sign, BIG white clouds of white smoke from a cold start.
My head gasket was bad, putting compression gases into the cooling system (this caused the air pockets, the coolant coming out of the radiator cap and because the cooling system was over pressurized, it eventually blew the gasket to the side tank of the radiator). When the car was no longer running and engine was no longer forcing compression gases into the cooling system, the over pressurized cooling system sent coolant back into the cylinders was it attempted to reach a "resting" pressure. That coolant is what made the slight rough idle in the beginning (it was such a small amount it did not make noticeable clouds, but caused small firing problems and blew out of the cylinder quickly). Towards the end, more coolant got into the cylinders and that's when the clouds got BIG!

By the time my GM friend got ahold of the car, he had a feeling he understood what the problem was by all the stuff I had gone through, but wanted to inspect a couple things before he said. The big thing he did was use a radiator pressure tester on the car to find out how long it took for the cooling system to become pressurized. Outside of that, he did not do much other then put all the pieces together to explain to me why it was a head gasket. After he told me, I ripped the car apart, sure enough the head gaskets both had a "crack" in them between the cooling channels and at least one cylinder (on both gaskets). After putting new head gaskets, LIM gaskets and a couple other "while I'm here" things, the car runs GREAT! That was at 180K in '09 and it's close to 220K now.

Sorry for writing a book, but I wanted to give you everything my car went though. By the fact you have clouds of white smoke, I think that's a BIG indicator. I am confident it is NOT an LIM problem getting coolant into the cylinder. If you look at the pic I attached (it was from when I did the head gaskets on the Grand Am). The 3100 and 3400 have the same basic LIM design. The coolant ports pointed with green arrows and the air intake ports with red arrows. In order for the LIM gasket failure to allow coolant into the cylinder, coolant would have to travel from a coolant port to the air intake port (the air intake port is where gas and air mix as going into the cylinder to then be ignited). Otherwise, any where else the coolant goes will basically end up in the engine oil or the crank case. From there, it travels as an oil/coolant mix and might get small amounts into the cylinder via that mix, but should not be enough to cause clouds.

I hope this makes sense and is of some help (though it's not a good answer of what needs done, especially with the 3400 in a venture van, that is just a PAIN).

 

The_Maniac,

Thanks for the reply. Yep, that's pretty much what the van looked like when I did the lower intake gaskets. I agree with everything you wrote there about he clouds of smoke, being more than likely a head gasket...but for what ever reason it doesn't do that any more. I can only guess what was actually happening, there was a tiny crack in the intake gasket and in valley where there is only RTV oil was leaking just a little. I know I'm just in denial about the head gaskets more than likely, once I get these other test done, like you I'll know for sure I think. Thanks for the advice and insight on your experience.

 

No problem. I wish I could say "it's 100% NOT a head gasket", but the evidence suggests too much to be a head gasket. But, I am NOT an expert on diagnosing head gaskets, so I encourage getting guidance from someone more experienced.

And I know my way around a 3100/3400 pretty good, but given the cramped space on a venture van, I cannot imagine trying to do much of anything on that drive train.