Rescue me and my overheating minivan

Rob:

I wonder if you can help me? I am at my wit's end in trying to repair my 1998 Chevy Venture van that I have owned since it was new - 145,000km.

After several repairs my van continues to have problems. Currently the temperature gauge will quickly go to the hot point (overheating) after it is started. The only way I can drive the vehicle is to turn the fan to high with temperature set at hot. By doing so the temperature gauge, as a max, only goes slightly beyond the midpoint. However, the temperature gauge swings between cold and the mid-point virtually every two minutes at highway speed and only cold air is coming from the heater vents.

To date I have replaced the intake manifold gasket, the water pump, the thermostat, the rad cap and the radiator. This has been done by two garages over a six-week period. There is no sign of coolant on the garage floor or indication that I am losing any. I cannot afford to keep this up and I may have reached the point that I turn the vehicle in for scrap since I do not want to pass these problems to someone else. Can you suggest anything?

Frustrated and much poorer, Bob

Yikes! Sounds like the 'ol shotgun approach yet again! Throw enough repairs at a vehicle and something's got to fix something!

Here's the thing Bob, Chevrolet had a series of overheating issues with the 3400 V6 engine -the one in your van. Interesting, because in one review of the 2010 Venture, mention is made of an overheat protection mode.

So, how does this help us? You have had enough work done to almost replace the top-end of your engine, with one exception - the head gaskets.

Before I go into this area, it would be helpful for you to find out a few details:

Were the parts Original Equipment Manufacturer (OEM)? When it comes to the critical pieces of a vehicle, the engine is WAY up there in the pecking order for OEM parts. I know there are those who may disagree, but there are differences in manufacturing processes and quality control.

Were both sets of intake manifold gaskets replaced?

Did the shop use the updated intake manifold gaskets?

That's a little homework for you Bob, before you take this to the next level - the head gaskets.

I'm going to assume that all the above issues were dealt with properly so that we can move on to the other failure area of the 3400 Chevrolet engine. Damaged head gaskets will cause symptoms to appear that you have described. What is happening is, combustion pressures are forcing exhaust gases into your cooling system creating an "air" bubble in the cylinder heads. Humour me with air bubble part; I'm using the term loosely. This process happens with each power stroke, or, each time a spark plug is fired. Then, on the intake stroke, coolant can be pulled into the combustion chamber and burned on the next power stroke. Many times this is where coolant mysteriously disappears to - no leaks - it just disappears.

Anytime you have anything other than coolant in the cooling jackets of the block and cylinder heads, you have no medium to carry the heat away. There is also no way to move that engine heat through your heater hoses which lead to the heater system inside your cabin. We have a double jeopardy situation Bob - and that's only successful on television game shows.

There's a few ways to determine if one or more of the head gaskets has gone away:

Look for a lot of steam at the tailpipe. This might be tricky with the cold damp air at this time of the year

This will be better: smell the exhaust at the tailpipe. Not too deeply Bob, we want you to continue reading GlobeDrive. What you are sniffing for is a sweet odour almost like caramelized sugar. If this is the case, the engine is pulling the stunt I mentioned earlier.

This step will require someone with an exhaust gas analyzer. At a shop, let the engine cool down to allow your technician to remove the radiator cap. Using the hose end tip of the exhaust gas analyzer, have that person hover the tip over the open neck of the radiator - do not let the tip enter the coolant, these analyzers act just like a vacuum cleaner, it will suck coolant inside and ruin the internal gas sensors. If there are any combustion gases in the cooling system, they will be sensed by the analyzer and the meters will light up like crazy. The readings will be higher than usually measured at the tailpipe because the readings are in front of the catalytic converters.

I hate to say it Bob, but you are at a "fish or cut bait" stage in your relationship with your Venture. Going into this deep will continue its hold on you, but if you're fine with that, carry on. 1998 - this is a 12 year old van, and worthy of introspection.