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Discussion Starter · #1 ·
I hate to post a new question so soon but I've used the search with no positive answers...:confused:

I just got a 95 MX-6 V6 LS With a stick trans, Has 120k, Hasn't been wrecked but was a daily drive (mother with kids from what i can already tell).

Question is:
At 60mph the RPM's are at 3k and when I'm going about 80mph the RPM's are closer to 4k. This seems kinda high for any car let alone a v6. So is there any guesses to why they are so high for highway speeds? (and yes it is in 5th gear)

I had the car checked out and it needs new brakes (i can do), the timing belt hasnt been changed at all so thats going to a shop and possibly a new head (saw a very small amount of oil coming from the top and while up on a lift they noticed some oil from the bottom).

Any help would be great. Thank you for ya time
 

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Those rpm's are normal for our cars. It is high, but the tranny isn't geared for highway cruising mileage I guess.

Our cars leak oil from many places, so don't go replacing the head just yet. A very common leak location is the valve cover gaskets. Around the valve covers you will see evidence of oil dripping down or within the spark plug wells you will see oil pooled up around the spark plug when you remove the spark plug boot.

Another common leak location is the OPSU (oil pressure sending unit).

Another place it can leak is from the distributor. There's an o-ring in there that can be replaced.

There's also the rear main oil seal, the front main oil seal and the cam seals. I don't think that any of these are particularly common, but the rear main is usually replaced when you do the clutch.

Good luck tracking down the leak(s)!
 

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Discussion Starter · #3 ·
I kinda figured that, But wasn't fully sure. Being i just got it less then a week ago everything seems fine. Anything i should also look at changing or upgrade (are intake, exhaust etc) first? Im going thru my basic car changes ,air filter, fuel system cleaner (seafoam) checking tire psi, Power steering fluid etc..

Also Thanks for the fast reply
 

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Does anyone know if having messed up timing would make the rpm speeds more for differebt mph speeds.... I brought my car out of storage today and my rpms seemed high for the speeds i was going and i had to re line up my disty. But i may just not be used to stick right yet its been 4 months
 

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Lol I thought the original poster said it's revving @ 3K when driving 60kmph then I realized it was mph.

Nah the revs are right. The engine is not that power, we aren't using massive V6s so the engine can't do 2k revs whilst going 60mph. There's just not enough torque to do it.
 

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Engine size doesn't have anything to do with the rpms at cruising speeds. The gear ratios make all the difference. Probe GT's have the same motor as the mx6 but a different gear set and they cruise at higher (if I remember correctly) rpms on the highway than we do.

There are 1.8 liter hondas that can spin 2k rpms in 5th gear while doing 65-70. I don't know what trans they are using but it makes for great fuel economy. You would just have to down shift a few gears to pass someone. :shrug:
 

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Discussion Starter · #8 ·
Guess i will just have to use gixxer to cruse on the interstate.
You would think a 6th gear would lower the RPM's for better gas economy but I'm pretty sure none of us have the money for a custom transmission...
 

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Discussion Starter · #9 ·
Does anyone know if having messed up timing would make the rpm speeds more for differebt mph speeds.... I brought my car out of storage today and my rpms seemed high for the speeds i was going and i had to re line up my disty. But i may just not be used to stick right yet its been 4 months

Honestly i was thinking the same thing about my car :rolleyes:
But being it would be more on the transmission then the engine, i would also have to say no. From what i can recall is you should be able to get some sort of sign on whats going on with you engine by looking at the spark plug(s). Here are some likes to charts on spark plugs. Hope this is helpful to someone:tup:

Road Star Clinic - Guide to Reading Spark Plug Performance
Century Performance Center, Inc. :: Spark Plug Reading

Otherwise i sure as hell would have a shop adjust the timeing is need be
 

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Engine size doesn't have anything to do with the rpms at cruising speeds. The gear ratios make all the difference. Probe GT's have the same motor as the mx6 but a different gear set and they cruise at higher (if I remember correctly) rpms on the highway than we do.

There are 1.8 liter hondas that can spin 2k rpms in 5th gear while doing 65-70. I don't know what trans they are using but it makes for great fuel economy. You would just have to down shift a few gears to pass someone. :shrug:

Not to be rude but engine CC does make a big difference. My gfs car is a 3.5L V6 and it can cruise at 2200rpms when going 65-70mph. Same idea with V8s, more CC, more torque and more ability to cruise at lower rpms.

Pretty sure that my gfs engine is making way more torque and power @ 2200 than any DE or ZE is at the same revs.

The gear ratio is what decides the rpms but our K series engines are revvy and not real powerful down low.

Also, I dunno about some honda 1.8L cruising @ 65-70 doing 2000rpms. Maybe if the car weighed 900KG that might be possible but the laws of physics would say that the engine simply wouldn't provide enough torque at those revs to maintain 65-70mph, it would be lagging so much that it'd probably less efficient than if it was running 3500 rpms. Unless the car is super duper light.
 

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Also, I dunno about some honda 1.8L cruising @ 65-70 doing 2000rpms. Maybe if the car weighed 900KG that might be possible but the laws of physics would say that the engine simply wouldn't provide enough torque at those revs to maintain 65-70mph, it would be lagging so much that it'd probably less efficient than if it was running 3500 rpms. Unless the car is super duper light.
It's not a matter of weight untill you get to a hill. It's about speed, frontal area and torque at a given RPM.

I think our engine has plenty of torque to cruise at 2K but performance would be compromised and I dont think there would be much of an improvement in mpg if any.

When an OE adds a feature like overdrive or a sixth gear with a taller oD ratio they typicaly quote about a 5% improvement in fuel enonomy, I would rather have the ability to pass at will.
 

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Also, I dunno about some honda 1.8L cruising @ 65-70 doing 2000rpms. Maybe if the car weighed 900KG that might be possible but the laws of physics would say that the engine simply wouldn't provide enough torque at those revs to maintain 65-70mph, it would be lagging so much that it'd probably less efficient than if it was running 3500 rpms. Unless the car is super duper light.
He doesn't say what rpm he cruises at in 5th but the gears must be pretty tall for him to be doing 80 in 3rd gear. 1993 Del sol's are listed at 2300 pounds.

Post #3

http://www.mx6.com/forums/gallery/219838-my-new-del-sol.html
 

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Discussion Starter · #13 ·
Ok i want to add to this as for RPMs and cruse speeds. I also have a 95'dodge intrepid(3.5L) Not sure if its a V6 but it IS a 6 cyl. That this has a much lower RPM range on teh interstate and honestly... being at 160k+ miles it get much better MPG then my MX6. That is more on the interstate. Both cars are about the same in town.
My point being, the LESS RPM's are car has to traval at the less harder the engine has to work to build up RPM's. So in some ways a car that can cruse at 2200 rpms *Mazda6*
just may be better at on gas. I wont disagree that being able to pass someone at will is nice but with the BHP of a MX6 should gas decent MPG and a lower cruse speed... just may not be able to pass as many cars.
 

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I reckon it is geared pretty well.;

so what if 100kph is 3000rpm. I'd prefer to drive my mx6 there then at 2k down a highway. Reason - 3000rpm the mx6 feels a lot nicer, its smooth, it loves this rpm band for cruising. It's also very economical at that speed, is beginning to develop some torque which means it can deal with hills etc without needed to gear down. Basically its where mazda designed the car to cruise at. I'm sure if mazda thought the car cruised better at 2k they would have geared the car to cruise at 2k.

I bet that little honda would need to changed gears at the slightest wiff of a hill.

I know my parents ford falcon (4.0 I6) cruises at about 1800rpm doing 110/120kph... but yeah.. that is sort of what that engine is built for.


^and iexion... WTF? no.... The HIGHER the rpm the easier it is to build RPM.
well... sort of. The closer to max power the easier to build RPM..... cause the car has more power.....
 

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there is a tradeoff between rpm/torque and mileage.

higher rpm = more power available = don't have to push the gas as hard to maintain speed

lower rpm = less power = having to give more throttle to keep her going

most people think you're using less fuel because you rpms are lower....but if you're at 20% throttle at 2500 rpm vs 16% throttle at 3000 rpm...would take some calcumalations to see which would achieve a better mileage.

case in point would be climbing a hill. Its probably better for mileage to downshift to 4th and get a little more rpm (power) going than to floor it in 5th just to maintain speed.
 

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Discussion Starter · #16 ·
I reckon it is geared pretty well.;


^and iexion... WTF? no.... The HIGHER the rpm the easier it is to build RPM.
well... sort of. The closer to max power the easier to build RPM..... cause the car has more power.....
I types that out wrong :lol: yes your right
Higher RPM's = more gas is used. Im not talking about power im talking about getting up to speed. So if a 3 liter engine doesnt take very much RPMs (1800rpm)/ gas to get up to speed this can allow the engine NOT to use higher RPM's = better MPG. Yes I know Higher RPM's is where the power band is (hints why a dyno can read 354hp & 7000tq @ 5600rpms) but that also sucks up gas... well unless we are dealing with a well tuned engine
 

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well yes... at WOT more rpm = more fuel.

but... partial throttle at higher rpm vs WOT and low rpm ... higher rpm can easily use less fuel.
 

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... the rpm will not fall when you are cruising just because you replaced spark plugs.....

not unless its interference with the tacho signal thats changing your rpm.

if there wasnt any interference changes then you were driving a hair slower this time.
 

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Discussion Starter · #20 ·
Im talking about replacing worn out spark plugs for maintance... Being the new plugs produce a better fire then the old plugs = more efficient and YES IT CAN LOWER RPMS (. Its a very small amount) and give some better gas mpg ( again a small amount) but any little amount can help.
 
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