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Possible to run water pump backwards

Chrysler is comming out with a new engine for 2011. It is called the “Penstar” and has a displacement of 3.6L. There is a warning published about this engine that demonstrates how incorrect routing of the serpentine belt can cause the water pump to run backwards. this would certainly be a tough one to diagnois. I wonder if this possibility exist with other engine types.

Yes. I’ve seen this a couple of times through the years. One was a 4.0 Jeep Cherokee and the other was an Oldsmobile. Correct routing of the serpentine belt is very important.

Several water pumps will operate equally well spinning clockwise or counter-clockwise. I don’t recall ever seeing a pump design that would reverse the flow when turned the wrong direction.

No effect of the pump running backwards was given, it was simply stated that “care must be taken to route the belt correctly so as the pump will not run backwards”. It is fair to ask what the result of the pump running backwards is, all that can be counclued from this article is that this paticular writer did not think it was a good thing.

It was also stated that soon this engine/vehicle will go to electric steering and thus a new routing procudure will be presented.

We are seeing evolution in vehicle design and we cannot get stuck in a “well I have never seen it matter before” mindset with this and other systems. From what I read I conclude that development of the automobile continues (and this development/evolution is a good thing).

Most water pumps that I have seen would still pump water in the correct direction if spun backwards, but would do so at a much lower flow rate. This is similar to AC blowers. If you wire the motor backwards, you still get airflow into the cabin, but you only get about 10% of what you would get with it spinning in the correct direction.

90% reduction in flow rate from a waterpump could be considered a issue of some significance.

I have(correctly) installed identical water pumps on engines with some turning clockwise and others counter-clockwise. I have also diagnosed overheating problems that have been caused by the incorrect water pump being installed. Water pumps use impellers, apparently some are bi-directional while others aren’t.

While the scenario is slightly different, the small block Ford water pumps can run backwards. The V-belt pumps run one way and the serpentine models run the other. Since the pulleys interchange and the pumps are similar in appearance it’s possible to install the wrong pump with the correct belt routing and have it run backwards.


A centrifugal water pump will not pump water running backwards…Most vehicle engines use belt driven centrifugal pumps…

These pumps seem to be specifically marketed as bi-directional.

The main point of my post was to alert people that it is possible for someone to get the belt routing wrong and cause a hard to diagnois overheating condition. I myself would not have even thought to explore the possibility that the belt would even fit correctly if it was not correctly routed. I did wonder if the possibility existed on other engine types to get a belt on in what at first appears to be correctly routed but in fact would end up turning the pump backwards and what consequences would be seen.

Some here are saying that no consequence would be noticed from the pump running backwards and some are saying that there will be an issue. I guess the safe thing is to just pay attention and route the belt correctly.

The problem is that many pumps have the vanes at an angle. This makes them pump very well when turned in one direction, and very poorly when turned in the other direction. Those that have the vanes pointed straight out will pump just as well whichever way they are turned.

On the vast majority of cars and trucks the serpentine belts are grooved on one side and flat on the other. If improperly installed there would be an obvious mis-match of grooved to un-grooved surface. Mis-routing the belt would likely cause some problem, if not overheating from poor water circulation, there is still the issue of the fan turning backwards on some vehicles. And the power steering pump would quickly lock up or cavitate and become noisy.

If there were a market for it I would write a book on the outrageous and ingenious patches and mistakes that have shown up at my door over the years. And one was a mis-matched water pump and fan(reversed rotation) on a Chevrolet pick up. I couldn’t believe that the truck had been to 2 dealerships and several private shops who made all kinds of exotic and far fetched guesses at diagnosing the overheating when driven but running perfectly cool when parked with the hood open.

I guess if you are willing to accept greatly reduced efficiency you can design a centrifugal pump that will work in either direction…Most centrifugal pumps have their outlet port angled to take advantage of the rapidly spinning fluid and allow the fluid to exit the pump with minimum turbulence…The bi-directional pumps with their 90 degree exit port are a compromise needed for specific applications…

The same issue of Motor magazine that contains the article that I passed on in my notorious TPMS system thread and the "End of an Era in Troubleshooting Techniques thread(that is where this information came from also) has a picture of both the correct and incorrect routing and there is nothing about the incorrect one that would draw your attention to it.

The picture/drawing was not detailed enough to see if ribs or grooves should draw your attention to incorrect routing as this certainly would be obvious.

Motor magazine is a ‘trade publication’ and often passes on the information to independent shops that manufacturers have given to their franchised shops. It would seem that they take it for granted that the reader is very familiar with problem, but general repair shops are not as up to date on newer models that are still in warranty.

And your comment relates to what and how?

Yo missleman…I have a 4.0 jeep and recently had problems with heater throwing heat. I had replaced the serpentine belt. My question…as long as one follows the proper routing there shouldnt be a problem. I guess i dont follow from the initial question. It seems simple enough. rout belt proper n no problems. What am i missing

I have a question.I have a 88 mustang 302. I changed the front cover so i could use a mech fuel pump changed the water pump.This is stuff i had laying car was a serptine belt.What i but on came off a v belt engine.So the pump runs backwards does that mater