One of the reasons is a cold intake deposits a lot of fuel on the runner walls - called port wetting. Once the engine starts, the amount of port wetting stays in relative equilibrium, decreasing as the manifold temp increases. It does take a lot of fuel to wet the ports on initial fire-up, however. You can think of this as lost fuel - fuel you are putting into the motor that does not actually reach the combustion chambers - at least initially.

Mitch

Is there port wetting on an MPI engine? Most of the fuel is down close to the intake valve.

Sam

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With a four mile drive to work, I'd bike it.

Dan and I had an interesting conversation in the other EFI thread about manifold heating. In your case I kinda doubt that in four miles anything warms up to any great deal. Something kicking around in the back of my head is a heater: diesels these days tend to use glowplugs for starting, but I recall a few using a heater in the intake manifold to directly heat the intake air.

[I used to own an '86 Izusu Pup, and at one point it ran badly; a SWAG from at least one mechanic pointed to some electrical heater installed below the carb, possibly having cracked and leaking air. Never determined if that was the issue, as I found the real problem: I had swapped some vacuum lines after reinstalling the engine for a leaky rear main seal; fixing the vacuum line swap fixed the issue. But there may be a precedence for post-carb electrical heaters. I'd check, but I long ago got rid of the truck, and any manual that I might have had for it.]

Now, such a heater would add considerable battery drain, and still won't provide instant heat. So maybe it's a non-starter. But if you want to fix this mpg issue, maybe plugging in a block heater (use a timer, have it kick on an hour before leaving) or something similar would help with these short trips. You'd still want to get the cold-cold engine starting fully dialed in; but perhaps a block (intake?) heater would fix these short trip mpg's for you.

A block heater sounds like a great idea for the trip to work. Not so sure about the trip home. I would have run and extension cord to the parking lot. Our work location is moving in a month or so to a space about 2 or 3 miles further away. Although total gas used will be more, the MPG's should be a bit better. It will likely be better for the car to get warmed up.

I would love to ride a bike to work, but live in a terrible area for biking. Add to that the frequent afternoon thunderstorms, and it gets to be not such an appealing idea. One of our employees tries to ride his bike to work. The storms have left him hitching a ride home often. His bike is many times still sitting there the next morning when I arrive.

Sam

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Well, an improvement would be an improvement. The engine's coldest temp ought to be after sitting overnight in the dark. So a block heater in the morn might get you over half the improvement of a block heater morn and evening.

Another thought: the grid heater in the intake, running off the battery, could use the extension cord on a trickle charger instead. That way you could better tolerate short trips that might run the battery down.

How are you injectors angled? I wonder if too much of the spray is hitting cold metal. Then again, if it sprays before cranking, there's not much that can be done about that. Are the injectors are good and clean, and fuel presure at the injectors is good and high?

Injectors have the standard angle toward the intake port. They pretty much spray as directly into the port as they could be. I think the injectors are pretty clean. I just ran a can of BK 44 through it.

Any tips on a black heater of good repute?

Sam

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'fraid not. Never gone shopping for one.

Question: did your manifold have provisions for coolant heating? I can't remember what you have. But I wonder if, if your intake manifod had that, if you could find some block heater which worked by heating the coolant; and thus heating your intake manifold.

That is a great idea. Yes, there is a provision for heating the intake with coolant. But you know the old Dutch proverb, "Too soon old. Too late smart".

When I installed everything I left the plugs out of the bottom of the manifold where the coolant reservoir is. And now, the Dutra Duals are in the way. There are plugs on the sides as well, which I could use for inlet and outlet, but the lack of plugs in the base would create a pretty substantial leak in the cooling system.

IF and WHEN I take everything off again, I will try to get plugs in there so I can plumb the coolant to it. Another thought, but not as potent I am sure is that there is a coolant passage in the TB. I have never plumbed this. They require quitei small tubing compared to the heater, and have not investigated the availability of T fittings with the larger size T'd to the small size. Nor have I investigated the best stategy for cutting into the heater lines. It might help some. But there would be now where near as much coolant in the TB as the manifold would hold.

I will absolutely put that on my list of things to do when it is possible to do it without undue effort. The turbo manifold is standard steel, and at some point I intend to remake it in stainless. When that happens, the intake gets coolant heat. Good thinking Supton.

Sam

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Actually, less coolant should heat up faster.

Again, I'm not sure what is out there. But on my VW TDi, it has the standard four glowplugs, one in each cylinder. But then it also has three very similar plugs in the coolant, in an attempt to get the engine up to temp faster. I think each one pulls 5 to 10 amps. Just pointing out what I know of, off the top of my head.

It would heat up faster, but would not retain the heat as long at short shut down times.

Sam

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