Sages,

So relating to a previous post:

https://www.brickboard.com/RWD/volvo/1636869/220/240/260/280/fresh_air_vent_always_closed_regardless_button_position.html

I've had a "hissss" out of my passenger side foot well when I shut the car off.

So my question(s) are a follows:
1. What causes this?
2. Will this effect my gas mileage?
3. What effect does this have on the engine performance?

I'm asking as I just took the car on part of a long distance shake down cruise after completely tons of repairs and upgrades and I was expecting to get better than 25 MPG on the first part of the trip. Currently I'm attributing the poor mileage to heading over all the mountains in western Md, and West Virginia, and to the fact that I was driving the posted speed limit of 70 mph.

I'm also asking this as my new me purchase of a 90' makes the same hissing sound when you shut it off, though all the vents appear to be operational, though I have not personally checked each one yet.

As always, thanks in advance to any and all information posted here.

Matt

25 mpg is perfectly normal even great for what driving conditions you describe
be happy!
--
'91 244 200k auto

Silvermine,

I guess I should not be concerned as most of my daily driving is at 55 mph and at around 2100 rpms, which puts my MPG around 30mpg. I'm now driving 70 mph, with RPMs at 2700 so I guess I should expect worse MPG.

Was hoping it would be better than my daily driving, though it is not.

What's interesting is that my wife's 98' S70, which is only a 4speed automatic, gets around 30MPG when doing the same trip. I guess newer technology has a lot to do with it.

I am happy with it as it is better than my 89' was when it lived a life as a 3 speed w/overdrive. Its MPG was horrible any time you took it out.

Thanks,

Matt

With respect to mileage. I have two 93 Classics both with AT. Last trip from New Haven to Cincinnati I saw 25.8 to 28.6 mpg in the sedan, slightly less in the wagon. 93 octane fuel, Delo 10W30 oil. I've taken I - 68 through Maryland and WV. Mileage dropped to 23-24 mpg. Hope this helps.

Sam

That mileage for the Md and WV mts.
Assume you have an automatic? That's what I get in my wagon with a 5Spd.
Even less with a rack and a couple of kayaks on top.

CB,

I have a 5 speed manual.

Gas mileage seems to have gone up a bit now that I'm not on any mountains and all flat.

Matt

so I'm running an 87 which you can alter the timing. Specs 12 BTDC +/-2deg. I go for the minus, so toward the 10. Of course the Knock Sensor takes care of the pings.

on trips to Philly and NY - the flats - I get 28-29 full throttle on the flats. Run Regular gas what is now called 87 octane, but then it's 10% Ethanol. so who knows.

Westward ho the sucking sound starts at Sidleing Hill and dosen't stop until I return and drop down from the Visitors Center----to the Great Midland Flats...and finally the downhill off the Appalachian Trail into Frederick

When I go out to the mts I pour in 89 octane from the pump. Thinking the higher "octaine" will stop the knock sensor from changing the timing. I can actually feel the difference on those 3 hills before Cumberland...the Divide.

So is that specious reasoning??? It seems to run better out there with 89 in the tank. So for weekends I'll run 2 fills of 89.

this is thru almost 20yrs on this beast...August 97

Your losing pressure in the plastic cannister. Might be the one way vacuum valve on the intake manifold(passenger side) half white/half black which is where the vacuum pressure comes from. Easy enough to remove and test for leakage.

Joekidd,

Ok, I can explain that in my 91' as I have a leak in the fresh air / recirc bellow , but have not had a chance to replace yet. Would this be causing any performance or gas mileage problems while driving as the white plastic bottle is always leaking?

My 90' however, I do not know its current state. I will pull a vacuum next week on the white plastic bottle and see what happens. I will also check the valve under the hood.

Thanks in advance,

Matt

Or the lines going into or out of the air director. Change the button settings and verify it does not change the hissssssss sound or duration

This is exactly what caused hissing on a '90 I used to own.