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May 2011 Top Tech Questions

Diesel Tach, Synthetic Oil, and More!

May 1, 2011
Diesel Tachometer
Question: I have a ’92 Dodge Ram that came from the factory without a tachometer, and I would really love to mount a nice, big, monster tach on my dash! How can I get a signal to run a tachometer?
Keith Stutter
Photo 2/4   |   Big, nasty tachometers with shift lights are something diesel performance is missing out on, and trust us, when to shift a diesel engine is every bit as important as in a gas-powered rig. If you want to run this type of tach, you’ll need a sensor that counts the teeth on your diesel’s flywheel, which can be found here:
Answer: There’s a few different ways to install a tachometer on any diesel engine. There are companies (such as Auto Meter) that make tachometers specifically for diesels, which pick up an rpm signal from the alternator. These units may require some calibration, but once they’re set up, they are very accurate. A second alternative, if you want to run any kind of tachometer, is installing a sensor that will send out a gasoline-style tach signal. If you go this route, you can also run all sorts of other electronics that are specific to gasoline engines, such as shift lights and air shifters.
Yet another option is to permanently mount a GTech Pro SS, which must also be calibrated, but once it is, it will read rpm, has a built-in shift light, and can measure g-force during acceleration as well as horsepower. The GTech is helpful in that it offers some data-logging capabilities, such as measuring rpm drop after shift points, shift time between gears, and more. You could also probably rig up a factory version to work, but we like the idea of a monster tach with a shift light, so we’d probably go the traditional V-8 tach signal route.
Synthetic In A Diesel?
Question: I own a Duramax that has 125,000 miles on it, and I am trying to find out whether or not it is OK to switch over to synthetic oil. Some mechanics I have talked to said it’s too thin and won’t work. Any insight you have would be appreciated.
Darrell Goins
New Caney, Texas
Answer: We’ve heard of people switching over to synthetic oils with no issues, but we talked to a few Duramax specialists just to make sure. The comment that synthetic oil is too thin doesn’t hold any water with us because you can buy different viscosity engine oils. When you hear that kind of nonsense from other people, it’s our guess that someone tried running normal gasoline-spec synthetic in their diesel and screwed something up. It’s been said that synthetics don’t allow new engines to break in as well, but with 125,000 miles on the clock, you shouldn’t have to worry about that. If it were us, we’d fill up with a diesel-specific weight such as 15W-40 (which they do make) and not worry about it.
Photo 3/4   |   Synthetic oils are perfect for the hard use of a diesel engine. In fact, many European diesels come with synthetic oils already in them from the factory.
It’s also stated that synthetic oils have better lubricating properties than oil made from dinosaur bones and ancient algae blooms, so it may be possible to achieve a slight increase in horsepower or fuel economy by running synthetics, but we wouldn’t count on feeling it. If you have an engine that doesn’t contaminate the oil very much (no or low EGR), then you can also run the engine a bit longer, mileage-wise, between oil changes. We’re not sure how the myth got started about not running synthetic oil in diesels, but in the case of your Duramax, it should be 100-percent safe.
Hit-and-Miss Stroke
Question: I’ve got an ’08 F-450 with a 6.4L Power Stroke engine. Its problem is that when warmed up, a low-sounding whistle emanates from behind the center of the dashboard. It’s rather loud, fairly consistent once it gets going, and it is something like a cross between a mini-hurricane and someone scratching their fingernails on a chalkboard behind the dash. It’s hit-and-miss, not consistent, and our local dealership is at a loss.
I’m also wondering if that issue is somehow tied to the massive amount of white smoke that comes from the exhaust periodically. And I’m not exaggerating when I tell you, it’s a lot of white smoke that will belch out down an entire onramp. Any ideas?
Danny L. Gentry
Via email
Answer: Your white smoke issue is most likely your intercoolerthere’s actually a technical service bulletin (TSB 08-25-1) from Ford about it. Moisture can collect in the intercooler and will give the engine a big shot of water the first couple of times you floor it, which will create the white smoke you’re seeing. We actually answered this question a few months ago in our tech section, but it seems not everybody knows about it, so we’re circulating it out into the world for a second time.
As for your hissing dashboard, it is most likely some kind of pressure leak in the engine. But where to start? It could be coolant, boost, or exhaust related. We’ve actually ridden in a truck like this that had the same kind of issue, and it turned out to be an intake manifold problem (the one into the engine, not into the turbocharger). Unfortunately, it’s hard to climb out of the truck and sit in the engine bay while getting on the throttle, so we’d suggest finding a place that has a chassis dynamometer that can load the truck to just under full power. The pressure leak may be in the engine’s exhaust manifolds, intake, turbochargers, intercooler bootsbasically anything that is under pressure could be a culprit. With the truck on a chassis dyno there will still be a lot of engine noise, but a boost leak will be easier to pinpoint, assuming it gets worse when the truck is under power. We’d start with the intercooler boots and engine intake gaskets and move on from there. Unfortunately, this type of search takes time, which is something not all dealerships are willing to commit.
Photo 4/4   |   Even if the problem is a mechanical one (like a boost leak), it can be a nightmare to find in the maze of complexities that is today’s diesel engine.
Welcome to Top Tech Questions. Oftentimes, readers contact us with questions about articles, or to praise us on what a good job we are doing. But our favorite form of reader communication is tech questions. Our Top Tech section is a place where you ask what’s on your mind, and we answer it. Got a trouble code? Wondering how to get your engine to make more power?
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