454 operating temperature

[tiinytina]

Sent: 1/29/2007

Hi all,
     229 miles from home, pumping 60 gallons of gas into a, was full when we left the house 80 gallon tank (3.4mpg), Running a 1987 Chevy 454.  Temps were upper 30's lower 40's driving in snow then rain.
   Mechanic said the cold humid temps were to blame for the poor mileage.
   I did notice that the dash temperature reading was not even to the 1/4 mark. I'm wondering if my radiator thermostat needs replacing. The radiator fan does kick on when parked and idling (for warm up)....  Driving back the 412 miles in sunny mid 40's temps the dash temp never got above 1/4. It doesn't crack any higher when idling.....
   I'm just wondering if the engine is running too cold to be efficient. Air coming from the cabin heater is warm but not hot at the highest setting. Another guy we met in Ohio at Sandusky who is a mechanic said maybe our "H" valve is bad as well (this shunts heat between radiator and cabin heating system).... 
   We averaged 5.5mpg on the way home... which was way short of our last fall run of 8.8mpg....
any advice?
Thanks
Tina

[jbmhotmail]

Sent: 1/29/2007

Tina,
Have you rebuilt that carb since owning your rv? If not, that may be some of the problem, be sure and replace the float, I used NAPA Echlin PN 2475 (brass float). Check out NAPA carb kits online, be sure and have your carb number. I use #72 main jets, #50 primary rods, #R secondary rod hanger, #EF secondary rods and GM PN 7029922 (7 to 3 inches HG) power piston spring (quadrajet carb). I also had my radiator recored (heavy duty 4 row) and my temp will not budge off the 1/4 mark. New 180 thermostat and new water pump. I was running a 15 lb pressure cap and was told by the "coffee shop free advice team" that if I lower the radiator pressure cap to 7 lb , I would run a little warmer. Never heard of this before but its cold in AZ (5100' altitude), so I'll try it.

Should be leaving for Quartzsite and Imperial Dunes (desert) next week so I'll let you know if the new cap pressure helps any.

Good luck
Jerry

[denisondc]

Sent: 1/30/2007 7:16 AM

* My limited experience with Chevys (two 350s, a 6 cyl 250 and a 4 cyl. 2.5L)is that their temperature sender units go bad gradually, resulting in the temp gauge indicating lower than normal, getting worse each season. So I would either try a new temp sender, or see if there is any place to install a mechanical temp gauge. Usually its hard to find such a spot. After that I would try a new thermostat; they can go bad fairly abruptly.
* In cool wet weather, if your engine doesnt have a 'manifold stove' to allow preheating the incoming air for the carburetor, you can expect some icing in the venturis - and Lousy Gas Mileage, even stalling. This is most prevalent when the air is a few degrees above freezing and the humidity high. The air temperature drop between the top of the carb and below the throttle plate can be well over 50 degrees fahrenheit when the engine is running. Even if your 454 has the manifold stove, the vacuum hoses, vacuum switch and diaphram that control pulling the hot air from the exhaust manifold, the parts might be moribund. Its possible the manifold stove has rusted off the exhaust manifold. This is all stuff thats totally un-needed in nice dry weather. I had a Lincoln with a missing manifold stove. In chilly wet weather it would simply stop running; if I didnt pull over each 20 miles, shut off the motor, and let the carb warm up from the engine heat. Our dodge based Winnebago never had a manifold stove, but nearly all of our use is in hot weather.
* Not only can the heater control valve be bad, but the heater core might be partially clogged. This is more likely to happen when the vehicle sits idle for long periods of time. The daily use that passenger cars get helps prevent the sludge from settling in the heater.

[MSN Member]

From: SPEC_OPS121
Sent: 1/30/2007

Automobiles are not like the airplanes i flew. you can't count on the gauges to be an absolute.

you can have the running temp. checked with an under the hood temp gauge just like you can with an under the hood oil gauge. most mechanics can do this.

it's not an impossibility that it was running too cold because it does have a desired temp that the engine is specd to run at. however, after 50 miles you should be up to running temp if the t'stat stayed closed until the block temp got up to the running temp and then slowly allowed some coolant to travel through the block until the temp was satisfied and then closed. this happens all the time in almost every car.

so, you either may have a stuck open t'stat, a rich running engine (but you'd see some evidence of this most of the time in blackish smoke. oil burn is more blueish)

some big rigs, 18 wheelers, actually have the radiator blanked off with a bra material than snaps on the radiator grille for this same reason when traveling in extreme cold weather.

best of luck. one day you wish it did run cool! lol

Stephen

[tiinytina]

Sent: 1/30/2007

We installed a brand new quadra jet carb when we bought "Gone". The old one was warped and was leaking gas. New seals, all vacuum stuff checked. Late last summer we removed the old air filter (with its crumpled and smushed input tube), and replaced it with a K&N filter assembly. We aimed the old air intakes at it but this is a "naked" filter assembly, just cover and bottom, filter exposed.  My mechanic said in cold weather we might experience "icing", so we kept the old assembly just in case. The engine however was running very smoothly(Just drinking gas through the McDonalds Milkshake straw...). I can feel the second set of carb intakes kick in when she is asked for more power on the highway so I don't think the carb is malfunctioning. Engine is idling a bit rich but no blue smoke etc on the road. She burns a "normal" 1 qt per 1,000 or so miles.  PO replaced all radiator hoses etc at idle I can hear the radiator fan kick on after a bit.

My first car a Datsun 310GX had a series of bad thermostats. 1 wouldn't open (overheating) 2 wouldn't close... finally the fourth one was fine (just a bad batch/lot number I later found out).

I'll see if I can borrow my buddies testing stuff and check running temps. I already have to replace wiper switches and windshield cleaner motor. So I'll be in and around her when I next get the chance.  Since the dash is... um huge, finding a spot for another guage if needed shouldn't be an issue if it is needed.

thanks! don't hold your breath on a resolution though... its about 24F right now, winter has finally arrived in MD....

Tina

[RV Mech Tech]

Tina - your comment  " I'm just wondering if the engine is running too cold to be efficient "  is correct  along with the other members and your mechanics comments - during the late 60's and early 70's the automanufactres got a taste of what was coming from the Federal emission standards and were 'pushed' into reducing the output at the tail pipe - fuel consumption and engine efficiency (volumetric efficiency) of most engines on the market for general use were 50-60 % efficient but still produced a lot of pollution -the car manufactures already had the technology for fuel injection  (more efficient metering of the fuel according to the demands at different RPM and load with electronic control as opposed to mechanical control on carbs)  but were in the process of making it inexpensive to produce on a mass production scale- so what did they do to meet the Federal emission standards each year? -they put bandaids on the existing engine and fuel and ignition systems - computer controlled carbs ( 'CCC' - we used to run out of the shop when one of these came in for service!!! LOL) devices such as the air cleaner with the thermostatic air valve at the end to control incoming air temp to keep the combustion temp above a certain level , higher cooling system pressure -the higher the pressure the higher the temp you can run without overheating the engine, also higher engine operating temp reduces most emissions except for NOX  ( oxides of nitrogen) and then they introduced EGR valves -exhaust gas recirculation valves (EGR) and on and on etc.- when one of these devices are disconnected gas mileage suffers and if your cooling system thermostat is not working correctly then that just adds to the problem -  and the final result is the volumetric efficiency falls off considerably and you use more fuel to produce the same amount of power at a given speed -I hope this gives you an idea of why the engine is consuming more fuel at cooler temps!    Hm?

[tiinytina]

We put the original snorkel/air cleaner back over the carb (I bought a KN to fit into it)... and we took of the "naked" KN assembly I had bought thinking more air= better mileage... the 454 needs the snorkel and all of its accompanying air pumps, vacuum hoses etc... these also prevent icing of the carb throat in cold temps etc... and yup. cold mileage back to normal... 6.4-7.6 with outlier of 8.4 sometimes on flat land...

Tina

[ttwitc9516]

Another prblem may be that in the north they change the fuel blend significantly from fall to winter and it adversely affects fuel mileage.  I dont know that it would reduce it by 50% but in my cars I have seen 20% from summer to winter.