The Mystery of Neil’s Truck
The image to the left is the under-hood of a Chevy pick-up. The customer’s concern was for a slow loss of coolant and this coolant loss was a bit of a mystery. Neil, the owner of the truck, reported that he would have to add a couple quarts of coolant every two or three weeks. His truck was always parked inside a garage and there was never any evidence of a coolant leak.
This problem is seen primarily on GM’s cars and light trucks. Here’s how it starts. The vehicle owner will notice that the coolant level slowly starts to drop. Usually there will be no sign of coolant on the ground. A pressure test of the cooling system could be inconclusive. You may get a brief smell or there may be no smell. The “no smell” can be the dangerously expensive one. Diagnosis of this mystery coolant leak requires a couple of inspections. The first inspection is of the engine oil level, dipstick and oil filler cap.
What are we looking for?
An overfull reading on the oil dipstick can indicate 2 possibilities; The engine oil is just overfull or there is coolant in the engine’s crankcase.
Why would oil in the crankcase result in an overfull condition? Coolant/water is heavier than oil. The coolant will settle to the bottom of the oil pan causing the oil level to rise in the engine. If this condition is found, another clue should be present. The oil filler cap and possibly the oil dip stick will have foamy build-up that is best described as a milk shake looking goo. This goo is the result of engine heat causing the coolant/water to evaporate and rise like steam escaping from a boiling pot of water. The Moisture condenses and collects in the high points of the engine.
In the event the engine’s oil pump should pick-up coolant, it will feed the coolant to the engine’s connecting rods and main bearings…, bang goes the engine!
The Good News, the Leak is External
The external leaks can be elusive. We first look for signs of coolant or stains on the engine block. Here’s what’s neat about this problem. In the early stages of this type of failure, coolant will only leak while the engine is heating up. Once up to operating temperature the the leak stops. This also means the heat of the engine will evaporate the small amount of coolant before any signs are seen under the vehicle or on the ground.
This condition can often be caught by pressurizing the cooling system when the engine is cold. Start the engine and as it warms up and watch for leaks. At just the right temperature the leak will present itself with the additional pressure on the cooling system from the pressure tester.
Pressure testing on Neil’s cooling system found the cause for the mystery. A failed intake manifold gasket was allowing coolant to slowly leak out of the engine. If Neil had ignored this problem he could have been buying an engine. Even though the repairs are still going to cost money, it is good news.
Now the Fix
Replacement of the intake manifold gaskets requires the removal of the intake manifold. This is easily said but as you look at the picture to the left you can see that there is a good amount that has to be removed. Clearly, this is no small adventure.
The cause for this intake manifold gasket failure? Plastic! That’s right.. plastic, the intake manifold gasket from GM is/was made of plastic. The intake manifold is not just about getting air into the engine. It also has coolant passages from the cylinder heads and the thermostat is located in the intake manifold. With age and exposure to coolant, the plastic becomes brittle and cracks. This results in failure of the sealing surface.
So why would the intake manifold gasket only leak at certain engine temperatures in the beginning? You have to realize, that the engine is made up of dissimilar metals. You’ll have the iron of the engine block, aluminum intake manifold and cylinder heads that can come either way, aluminum or iron. We know that metal expands as it heats up. The problem with dissimilar metals is they expand at different rates, in different amounts. Now throw a piece of plastic in between and you have a recipe for pending doom.
Poor Quality Original Equipment
The aftermarket was quick with the fix, they came up with a replacement intake manifold gasket that was far superior to the plastic ones provided by GM. To the left is an image of the failed intake manifold gasket. Click on the image for a better view.. That squiggly kind of light blue looking ring is the seal that is suppose to keep the coolant inside the engine, not outside. The distorted areas are where the coolant was leaking. If you look at the bottom of the opening you can see that the ceiling surface is starting to fail. If this section had failed completely, coolant would’ve entered the crankcase of the engine. Coolant in the engine oil could have resulted in a catastrophic failure of the motor.
Aftermarket to the Rescue
Here is a close up of the replacement gasket. Click on the image for a better view..When we perform this service to our customer’s vehicle they will only receive the new and improved gaskets. Not too long ago GM smartened up and changed their gasket design as well, guess what it looks like? If you guessed pretty much like the replacement aftermarket gaskets, you’re right.
When it was all said and done Neil’s truck was sealed up as tight as a drum… no more coolant leaks.
Today’s automotive world is changing at a blinding speed. It is not uncommon for manufacturers to change the design part way through the year. With so many changes there will be problems. One thing we’ve learned is that the aftermarket is quick to respond with fixes for design problems in today’s vehicles.
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