Pump and grindVEHICLE: 1988 Pontiac Grand PrixDRIVETRAIN: 2.8L engine, automatic transaxle MILEAGE: 154,684 miles COMPLAINT: Scraping noise with engine running.Circumstantial land mines: They can happen to any of us. A vehicle comes in with what seems like a routine repair or adjustment. You do the job right, and then the whole thing blows up in your face and leaves you reeling. For example …
It was the summer of 1984, and I was working for a VW dealer. I wasn’t even aware there was a problem until the man came to pick up his diesel Rabbit. I had adjusted the valves to factory specs, and I’d never had a problem like this with the dozens of other valve adjustments I had done. But by the time the customer returned, paid his bill and started the car, the engine had cooled, and the cam followers that carry the shims were fitting tighter in their bores. And because the valves had been incredibly loose, I had installed thicker shims. Now, the cam followers were traveling deeper, and each one of them was repeatedly sticking in its respective bore until the rising piston contacted the valve and bumped it loose. The resulting noise was alarming, to say the least, and it was loudest when the engine was spinning with the starter. I heard it plainly from inside the shop, and when I walked out to see what the noise was, the angry customer chewed me up one side and down the other, telling me he wasn’t paying another dime and that I would fix what I had fouled up.I was confused. After all, it had only been a routine valve adjustment, and there had been no running problem I had been trying to repair with the valve adjustment. With that in mind, the simplest thing I could think of was to undo what I had done and get him on the road. Having no idea at the time what had gone wrong, I quickly adjusted his valves back to their original looseness to stop the racket. I realized later that I could have removed the camshaft and the cam followers, then cleaned the bores so they wouldn’t stick when the engine was cold. The problem was that I knew the customer wouldn’t pay to have all that done. I had just stepped on a ‘circumstantial land mine.’ Have you ever been there? This experience was frustrating, but most of us would agree to the fact that the jobs from which we learn the most are the ones that slap us around. Techs who are familiar with these timing covers would expect to see this kind of smooth, slightly raised surface instead of the machined, indented surface on the bad cover.
It was the summer of 1984, and I was working for a VW dealer. I wasn’t even aware there was a problem until the man came to pick up his diesel Rabbit. I had adjusted the valves to factory specs, and I’d never had a problem like this with the dozens of other valve adjustments I had done. But by the time the customer returned, paid his bill and started the car, the engine had cooled, and the cam followers that carry the shims were fitting tighter in their bores. And because the valves had been incredibly loose, I had installed thicker shims. Now, the cam followers were traveling deeper, and each one of them was repeatedly sticking in its respective bore until the rising piston contacted the valve and bumped it loose. The resulting noise was alarming, to say the least, and it was loudest when the engine was spinning with the starter. I heard it plainly from inside the shop, and when I walked out to see what the noise was, the angry customer chewed me up one side and down the other, telling me he wasn’t paying another dime and that I would fix what I had fouled up.I was confused. After all, it had only been a routine valve adjustment, and there had been no running problem I had been trying to repair with the valve adjustment. With that in mind, the simplest thing I could think of was to undo what I had done and get him on the road. Having no idea at the time what had gone wrong, I quickly adjusted his valves back to their original looseness to stop the racket. I realized later that I could have removed the camshaft and the cam followers, then cleaned the bores so they wouldn’t stick when the engine was cold. The problem was that I knew the customer wouldn’t pay to have all that done. I had just stepped on a ‘circumstantial land mine.’ Have you ever been there? This experience was frustrating, but most of us would agree to the fact that the jobs from which we learn the most are the ones that slap us around. Techs who are familiar with these timing covers would expect to see this kind of smooth, slightly raised surface instead of the machined, indented surface on the bad cover.
With no real frame of reference, this timing cover looked fine at first glance. But after the new water pump was installed, this worn out part just wouldn’t let the pump move enough liquid to keep the block cool.The growling Grand Prix
I came back from lunch one day to find a group of my students clustered around a 1988 Pontiac Grand Prix with its hood open. It was making a nasty scraping sound, and they had already pinpointed the problem. The water pump on this engine is right on top and fits into the timing cover. Why some of the other manufacturers don’t make their pumps this accessible is beyond understanding.To make a long story short, the student who owned the car OK’d the replacement of the water pump, but first he wanted to drive the car to get some cash so he could pay his bill. I called the parts store and had a water pump delivered for the 2.8L.When my student got the water pump off, I took a quick look at the timing cover because the pump impeller spins next to a machined surface in the cover opening. I noticed some scoring where the cast iron impeller had contacted the timing cover, but it still looked serviceable. A few minutes later the new pump was in place, and the belt and pulley were installed. These engines are prone to get air bound; this one had a petcock on the thermostat housing but no other bleeder. I had the students take the heater hose off next to the water pump and pour the block full of coolant until it gurgled out of the radiator filler neck. I didn’t want any trapped air causing the 2.8L to overheat.The car’s owner came walking into the shop just as we were warming the engine and waiting for the thermostat to open. We had the petcock open and in a short period of time there was steam spewing out of the petcock, but no water.
“It was overheating at traffic lights”“Did it overheat before we changed the water pump?” I looked at my watch. It was almost time for the students to knock off, and we wouldn’t be back in the shop until Monday.“The hot light came on when I was stopped at traffic lights,” he answered, “but it always went off when I was driving. This is the first car I’ve ever owned that has no temp gauge, so the light is the only way I can monitor the temperature.”
“Usually, when the light comes on, it’s almost too late,” I said, shaking my head. I had seen Ford Tempos take that kind of punishment and worse without engine damage, but I wasn’t sure this 2.8L V6 had the fortitude to repeatedly handle the steamy temperatures that would illuminate the ‘hot’ light.This new information about the previous overheating problem thickened the plot considerably. Overheating at idle generated the idea of a dead cooling fan motor. I immediately pulled the cooling fan relay from the underhood fuse box and bypassed it with a jumper wire. The fan came on with gusto and pulled air through the radiator famously. But the Pontiac continued to overheat, and the radiator was surprisingly cool.These two micrometer readings tell the tale. It’s hard to argue with these numbers, especially when it comes to the difference a few thousandths of an inch can make on a water pump moving coolant through a hot engine block. The old water pump impeller had actually machined more than 0.070 inch off its mating surface (3a) in the timing cover.
I came back from lunch one day to find a group of my students clustered around a 1988 Pontiac Grand Prix with its hood open. It was making a nasty scraping sound, and they had already pinpointed the problem. The water pump on this engine is right on top and fits into the timing cover. Why some of the other manufacturers don’t make their pumps this accessible is beyond understanding.To make a long story short, the student who owned the car OK’d the replacement of the water pump, but first he wanted to drive the car to get some cash so he could pay his bill. I called the parts store and had a water pump delivered for the 2.8L.When my student got the water pump off, I took a quick look at the timing cover because the pump impeller spins next to a machined surface in the cover opening. I noticed some scoring where the cast iron impeller had contacted the timing cover, but it still looked serviceable. A few minutes later the new pump was in place, and the belt and pulley were installed. These engines are prone to get air bound; this one had a petcock on the thermostat housing but no other bleeder. I had the students take the heater hose off next to the water pump and pour the block full of coolant until it gurgled out of the radiator filler neck. I didn’t want any trapped air causing the 2.8L to overheat.The car’s owner came walking into the shop just as we were warming the engine and waiting for the thermostat to open. We had the petcock open and in a short period of time there was steam spewing out of the petcock, but no water.
“It was overheating at traffic lights”“Did it overheat before we changed the water pump?” I looked at my watch. It was almost time for the students to knock off, and we wouldn’t be back in the shop until Monday.“The hot light came on when I was stopped at traffic lights,” he answered, “but it always went off when I was driving. This is the first car I’ve ever owned that has no temp gauge, so the light is the only way I can monitor the temperature.”
“Usually, when the light comes on, it’s almost too late,” I said, shaking my head. I had seen Ford Tempos take that kind of punishment and worse without engine damage, but I wasn’t sure this 2.8L V6 had the fortitude to repeatedly handle the steamy temperatures that would illuminate the ‘hot’ light.This new information about the previous overheating problem thickened the plot considerably. Overheating at idle generated the idea of a dead cooling fan motor. I immediately pulled the cooling fan relay from the underhood fuse box and bypassed it with a jumper wire. The fan came on with gusto and pulled air through the radiator famously. But the Pontiac continued to overheat, and the radiator was surprisingly cool.These two micrometer readings tell the tale. It’s hard to argue with these numbers, especially when it comes to the difference a few thousandths of an inch can make on a water pump moving coolant through a hot engine block. The old water pump impeller had actually machined more than 0.070 inch off its mating surface (3a) in the timing cover.
I used a hacksaw on the old timing cover and installed a water pump with good bearings to illustrate the clearance that was actually present between the impeller and the housing. The old pump that had machined the cover rode a lot nearer to the housing and was actually more efficient in this cover than the new pump. This gap may not seem like much, but it certainly made a big difference with the pump spinning and coolant flowing.Blown head gasket?
The steam escaping from the thermostat housing petcock didn’t smell like a blown head gasket – yet. But I knew something was terribly wrong. The engine absolutely couldn’t have any trapped air, but the hot light had come on and wouldn’t go off.And the Pontiac was percolating like a Model A.“Shut the engine down,” I told the student who was monitoring the light. “Do you think I can make it home?” asked the owner, looking at the clock.“You can try, but I wouldn’t advise it. You may have a blown head gasket.” I knew he lived 30 miles away. and I pictured a steaming Pontiac sitting beside the road with the hood open just a few minutes up the highway.“The hot light always went off when I was in the wind,” he reminded me.“I still think you might have a blown head gasket.” I hoped I was wrong. He had already paid the work order on the water pump, and he decided to drive it up the road to see if the light would go out.“If the light doesn’t go out as quickly as it used to when you started moving, you’d better bring it back and call for a ride,” I told him. “Burning your engine up could ruin your whole weekend.” He headed out but was back a few minutes later.“It didn’t go out,” he told me as he dialed his cell phone.He agreed that we should have another look at it on Monday. In the meantime, I remembered another ‘circumstantial land mine’ I had stepped on a few months after the Rabbit incident. As I did a mental replay of that cool day in 1984, I figured out what was making the 1988 Pontiac overheat.Getting Out a Dodge
I had migrated that fall to a Lincoln-Mercury dealer to specialize in automatic transmissions and driveability electronics, and in the midst of my experiences at that dealership, the circumstantial land mine reared its ugly head again. The bookkeeper’s Dodge Aspen was leaking coolant from the weep hole in the water pump, and I swapped the pump in record time, replacing it with a reman pump from a local parts supplier. I went through the normal procedure of burping air out of the cooling system, taking it on a test-drive, and returning it to the owner. The next day he showed me his temperature gauge and told me the Dodge wasn’t exactly running hot, but that it was running a good bit hotter than it did before the pump was changed. I test-drove the car and found that it was running between the midway point and the hot line on the gauge. He asserted to me that before I had changed the leaking water pump it had been running below the midway mark. I had done absolutely nothing except change the pump, so I ordered another one from the parts supplier, not really knowing what to expect, let alone what to look for. When I got the first replacement pump back off, I compared it to the second replacement unit, and I saw a difference that would easily escape the naked eye. The impeller on the first pump had 0.050 inch more clearance between the blades and the pump housing than the second replacement. It actually made a surprising difference on the temperature gauge when the whole ordeal was over. I didn’t get paid for the second pump swap on the Dodge, just like I didn’t get paid for the second valve adjustment on the Rabbit. Getting the Dodge fixed the second time around was a circumstantial land mine I had pondered off and on down through the years, and in what I and gleaned from that particular experience, I found the key to the percolating Pontiac problem.Pay dirt on the Pontiac
When we resumed our lab on Monday, I filled out a new work order on the Pontiac, had the student sign it and told him we would replace the timing cover with a known good one before going after head gaskets. Buying an expensive cast aluminum timing cover on a “try it and buy it” basis seemed scary, so I decided to use the timing cover from an old engine we had on hand. With the existing timing cover removed, I compared the two and found that the bad water pump had done a lot more than score the timing cover. The old water pump impeller had actually machined more than 0.070 inch off its mating surface in the timing cover, leaving a sizeable gap that neatly neutralized the effectiveness of the new water pump. Riding on good bearings, the new impeller was whirling in the damaged timing cover with about an eighth of an inch of clearance, far more than a healthy water pump needs to do its job. With the new timing cover installed and a shorted A/C relay replaced that was blowing the fuse feeding the fan relay coil, the Pontiac ran as cool as a cucumber. The fan cycled comfortably, and the percolation and the hot light were both gone.And the lesson?
The next time you step on a circumstantial land mine, try to look past the lost flag time and focus on the value of the experience. The knowledge we gain during these trying situations generally pays far greater dividends than a few extra dollars on Friday.SIDE NOTE: Intermittent overheating diagnosisSometimes radiator cooling fans will develop an open circuit in one part of the armature that will cause the fan not to respond intermittently when current is applied. Usually, when the car is in the shop, the fan works without fail, effectively confusing the diagnostic process.
To check for this dastardly Roulette-type failure, you can disconnect the cooling fan electrical connector. Connect a test light in series with the motor and a battery, at which time the test light should illuminate.
With the test light in place, slowly rotate the fan blades while watching the test light. If the light ever winks off while the fan motor is being rotated, the motor must be replaced. When it stops in that dark spot, it won’t respond to the current feed that should start it spinning.
I’ve found that this test has successfully fixed a lot of cars that had been from shop to shop for intermittent overheating problems.
The steam escaping from the thermostat housing petcock didn’t smell like a blown head gasket – yet. But I knew something was terribly wrong. The engine absolutely couldn’t have any trapped air, but the hot light had come on and wouldn’t go off.And the Pontiac was percolating like a Model A.“Shut the engine down,” I told the student who was monitoring the light. “Do you think I can make it home?” asked the owner, looking at the clock.“You can try, but I wouldn’t advise it. You may have a blown head gasket.” I knew he lived 30 miles away. and I pictured a steaming Pontiac sitting beside the road with the hood open just a few minutes up the highway.“The hot light always went off when I was in the wind,” he reminded me.“I still think you might have a blown head gasket.” I hoped I was wrong. He had already paid the work order on the water pump, and he decided to drive it up the road to see if the light would go out.“If the light doesn’t go out as quickly as it used to when you started moving, you’d better bring it back and call for a ride,” I told him. “Burning your engine up could ruin your whole weekend.” He headed out but was back a few minutes later.“It didn’t go out,” he told me as he dialed his cell phone.He agreed that we should have another look at it on Monday. In the meantime, I remembered another ‘circumstantial land mine’ I had stepped on a few months after the Rabbit incident. As I did a mental replay of that cool day in 1984, I figured out what was making the 1988 Pontiac overheat.Getting Out a Dodge
I had migrated that fall to a Lincoln-Mercury dealer to specialize in automatic transmissions and driveability electronics, and in the midst of my experiences at that dealership, the circumstantial land mine reared its ugly head again. The bookkeeper’s Dodge Aspen was leaking coolant from the weep hole in the water pump, and I swapped the pump in record time, replacing it with a reman pump from a local parts supplier. I went through the normal procedure of burping air out of the cooling system, taking it on a test-drive, and returning it to the owner. The next day he showed me his temperature gauge and told me the Dodge wasn’t exactly running hot, but that it was running a good bit hotter than it did before the pump was changed. I test-drove the car and found that it was running between the midway point and the hot line on the gauge. He asserted to me that before I had changed the leaking water pump it had been running below the midway mark. I had done absolutely nothing except change the pump, so I ordered another one from the parts supplier, not really knowing what to expect, let alone what to look for. When I got the first replacement pump back off, I compared it to the second replacement unit, and I saw a difference that would easily escape the naked eye. The impeller on the first pump had 0.050 inch more clearance between the blades and the pump housing than the second replacement. It actually made a surprising difference on the temperature gauge when the whole ordeal was over. I didn’t get paid for the second pump swap on the Dodge, just like I didn’t get paid for the second valve adjustment on the Rabbit. Getting the Dodge fixed the second time around was a circumstantial land mine I had pondered off and on down through the years, and in what I and gleaned from that particular experience, I found the key to the percolating Pontiac problem.Pay dirt on the Pontiac
When we resumed our lab on Monday, I filled out a new work order on the Pontiac, had the student sign it and told him we would replace the timing cover with a known good one before going after head gaskets. Buying an expensive cast aluminum timing cover on a “try it and buy it” basis seemed scary, so I decided to use the timing cover from an old engine we had on hand. With the existing timing cover removed, I compared the two and found that the bad water pump had done a lot more than score the timing cover. The old water pump impeller had actually machined more than 0.070 inch off its mating surface in the timing cover, leaving a sizeable gap that neatly neutralized the effectiveness of the new water pump. Riding on good bearings, the new impeller was whirling in the damaged timing cover with about an eighth of an inch of clearance, far more than a healthy water pump needs to do its job. With the new timing cover installed and a shorted A/C relay replaced that was blowing the fuse feeding the fan relay coil, the Pontiac ran as cool as a cucumber. The fan cycled comfortably, and the percolation and the hot light were both gone.And the lesson?
The next time you step on a circumstantial land mine, try to look past the lost flag time and focus on the value of the experience. The knowledge we gain during these trying situations generally pays far greater dividends than a few extra dollars on Friday.SIDE NOTE: Intermittent overheating diagnosisSometimes radiator cooling fans will develop an open circuit in one part of the armature that will cause the fan not to respond intermittently when current is applied. Usually, when the car is in the shop, the fan works without fail, effectively confusing the diagnostic process.
To check for this dastardly Roulette-type failure, you can disconnect the cooling fan electrical connector. Connect a test light in series with the motor and a battery, at which time the test light should illuminate.
With the test light in place, slowly rotate the fan blades while watching the test light. If the light ever winks off while the fan motor is being rotated, the motor must be replaced. When it stops in that dark spot, it won’t respond to the current feed that should start it spinning.
I’ve found that this test has successfully fixed a lot of cars that had been from shop to shop for intermittent overheating problems.
