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Severe loss of mileage after engine work

'92 Honda Accord

My car was getting 28/29 mpg when the water pump went. Afterward the work was done the mileage dropped to ~21 mpg. Going back to the place that did the work is not an option. A few months after the work I decided to do a tuneup to fix the mileage. A guy from the parts store came out to show me how to deal with the spark plugs and told me I needed a new valve cover gasket. When I went back to the place that did the work, they agreed I needed a new gasket and would do it for the full price. They also agreed that they had just replaced it when they did the original work. Even I know gaskets don’t fail that quickly. So they did a foul job originally. What could they have done to kill the mileage?

Thank you,


To replace the water pump, the timing belt has to be removed. If the shop you used was any good, they would have at least advised you to replace the timing belt and balance shaft belt at this time. A sudden drop in gas mileage raises the possibility that the timing belt was not reinstalled correctly.

Worse case, if they did not replace the belt and they reinstalled the original belt to rotate in the other direction, then that belt could fail prematurely.

The valve cover gasket is reuseable if not too old, but whether new or reused, there are two small areas that have to have a sealant applied every time the valve cover is removed, otherwise it will leak. I suspect though that the guy from the parts store noticed oil pooling around the base of the spark plugs. Since the spark plugs are in holes in the valve cover, there is a seal for each one of them.

New seals come with a new valve cover gasket set. That makes me suspect that the mechanics who did the job on your Honda threw away the seals instead of replacing them and they don’t want to buy a new valve cover gasket set just for the seals, its not cheap.

If you have a Honda dealer nearby, I strongly suggest that you get an estimate for a timing belt job from them. I have a 97 Accord, which is the same generation as the 92 I believe and the timing belt job, which included a new balance shaft belt, a new water pump, all oil seals on the front of the engine, new valve cover seals, fresh coolant and a new oil pump seal ran me $735.

If you have more than one dealer, check them all. This was the second timing belt service I had done at a dealer. The first one, 8 years ago at a different dealer actually cost me more and I don’t feel they did as good of a job, I don’t think they got the balance shafts timed properly, which on this engine is really tricky if you don’t have the actual factory shop manual to show you how.

But the guy who did it this time got it right and the engine is much smoother now.

There’s a lot of missing info here so some assumptions could be made on my part.

Did this water pump failure lead to overheating and/or loss of a head gasket? (Per the valve cover gasket comment)

IF the timing belt is aligned correctly and if the ignition timing is correct and if the engine was severely overheated, then the point could be made that the engine suffered piston ring damage and lowered compression which will cause a peformance and mileage loss.
This could be the case even if a blown head gasket was replaced.

Details would help.

The car was warm when I pulled out of a parking lot and onto the highway. I forget what caused me to recognize the problem, most likely coolant billowing away. It was only three miles or so to the repair place. I thought it was a hose at the time. Maybe a gasket went, they did not mention anything to me.

What other information information falls into “lot of missing info”?

Was the timing belt changed?

Coolant billowing away could be very significant as that could denote a head gasket failure and driving 3 miles to a repair shop after noticing billowing smoke points to an engine that was considerably more than warm as you describe it. Some additional info would help.
Was the belt changed as keith has alluded to several times?
Did the engine suffer a head gasket failure and was that gasket replaced?
Why was the valve cover gasket changed; as part of a head gasket job or what?
What parts were charged out and what was the total bill?

That list of questions is a start anyway.

I was told that the water pump failed, no mention was made of the head gasket. The total price was close to $450. They had kit they used when replacing things like the water pump. A new timing belt was part of the job. The valve cover gasket replaced as part of the kit.

It sounds as though having a dealer re-do the job is the best of poor alternatives.

If it has a new timing belt, then if the mechanics are going to replace the valve cover gaskets again, it won’t be hard for them to double check the timing belt alignment, and if it is off, they can adjust it fairly easily.

@GeorgiaDuck, I’m a little confused about one thing.

Did you pay twice for the valve cover gasket?

It’s a bit murky to me also because a valve cover gasket should not be part of a timing belt kit and does not have to be replaced as part of a belt job/water pump job.

If they changed the valve cover gasket that begs the question of how does someone muck up a job like that?

As to the mileage loss, I would agree that the belt timing marks should be rechecked along with the ignition timing. If everything is well in that area then I’d run both a dry and wet compression test and make sure you’re dealing with a solid engine.

If you have the automatic, it’s actually only rated for 22 MPG overall anyway as you can see here

@ok4450, while a valve cover gasket may not be part of a timing belt kit, on some engines the valve cover does have to be removed to do the job.

Yes. I ended up paying twice for the valve cover gasket, having gone back to a previous shop.

I have no idea how they mucked up a valve cover gasket job. Long ago I did one on an AMC Pacer and didn’t manage to screw it up (only one I ever did).

My money is on the timing belt. I’m betting that they mistimed one of the camshafts.
I’ll bet Keith is right.

The distributor base allows for a few degrees of adjustment and advancing the ignition timing may significantly improve performance and mileage. Of course, the mechanic who replaced the belt should have confirmed the timing using a timing light.

A blown water pump will dump coolant on timing belt. I had a new wp leak and the parts store gave me new wp and timing belt. If u reused old tb with new wp than ur asking for trouble.

You do have to remove the valve cover in order to remove the timing belt cover on this engine. OK is right that the valve cover gasket set is not part of a timing belt/water pump replacement, but if the valve cover gasket has gotten stiff and hard, it has to be replaced.

It sounds like it would be worthwhile to have a dealer redo the timing belt. Not cheap, but it would pay for itself in a year.