Diesel Engines and Cavitation

[70Post455]

I am looking at purchasing a 1986 Ford F350 Dually 2wd 6.9 N/A with a flatbed. I have not purchased the truck yet and still have a few questions and I am still looking at a couple other F250 and F350’s for sale.
I also would prefer a PU with a box as opposed to a flatbed, however I could always pull the flatbed off and look for a nice ext cab dually box and install it.

Diesel engines and cavitation? I have read the information in the forum on tech tips. After reading this info I would feel a little safer purchasing a 6.9 over a 7.3, however if the 7.3 was/is owned by a knowledgeable person then I would feel fine.
The one thing I did notice is that short trips are not real healthy for a Diesel engine. I would probably not use mine a lot unless I was to pull the trailer for a longer trip.
I am curious to find out how many of you drive yours for a daily driver? Do you start it up and let it warm up for a while before you drive off to work or run your errand. I would love to give a diesel a try and would love the more heavy duty truck for pulling my car trailer over my current ½ ton PU, but am I barking up the wrong tree looking at this diesel since I do not go on a lot of long trips.
Also if you have a Diesel for sale you can PM me with some info. I am in the market and currently looking, but would prefer it be close to Nebraska, unless you are willing to meet halfway or find good not overly expensive shipper.

TIA,
Tom

 

[Mr_Roboto]

You should not let a engine 'warm up" by idling. All that does is keep it cold longer. If you are driving you will be up to operating temp in a few minutes.

The 6.9 is much less prone to cavitation damage, because the cylinder walls are thicker and so they flex less (the flexing is what causes the initial coolant cavitation).

I really don't think short trips are much harder on a diesel than a gasser. In both cases they cause the oil to foul because contaminants do not get boiled off.

 

[Agnem]

The Moosestang is a daily driver. Given the choice, I like to let them warm up until they "kick down" at least. But a lot of the time I just get in and go. I believe the metalurgy benefits from a slow temperature change.

 

[Dieselguy123]

my 6.9 is my daily driver, I usually let it warm up about 1 min and then hop in and go. Most of my driving is short trips......less than 10 miles, the truck doesnt seem to mind.

 

[Optikalillushun]

i just wait bout one minute to let the oil pressure get up and oil to where it needs to go.

 

[Andylad13]

the only thing you really need to do is cycle the glow plugs when you start it, and make sure every component of the system in in full working order all the time. i am also one of the people who will only let it idle for about 1 minute. the longer you wait while idling, the more your oil breaks down without adding mileage letting you know when to change it. take the dive into diesels!!

oh yeah and about pulling your trailer, your going to like the whole "i'm going to pull this trailer and not have much affect on fuel mileage" thing.

 

[RLDSL]

I let mine warm up until the fast idle kicks down. They've made engines to where they'll scoot out the driveway right after turning the key to cut down on emissions, but it's still not the greatest thing for the engine. I like to let the internals warm up enough to where the pistons have enough time to expand so they aren't slapping around in there under load prematurely wearing the skirts off, and the heads aren't having to slide around on the gaskets from uneven heating anymore than needed., not to mention that diesels can be a bit gutless until the combustion chamber warms up .
Besides, if it's cold out, it'll take that long to clear the windows anyway.

Once they've been run for the day, they'll usually be ready to go most of the day unless you're in serious cold country. I've got a number of diesel cars along with the truck, and they all get warmed up first shot of the day, and my wife lets her diesel car warm up good when she's coming home late after it's been sitting for 12 hours. Rest of the time , it's jump in and go.

I had one friend in Fairbanks and he'd plug in overnight and make sure to go somewhere at lunch on REAL cold days to keep his diesel car ready to go

Short trips wont hurt diesels, you just need to remember to wind them out good once in a while to clear the carbon buildup , some fuel additive to keep the injectors from loading up ( and with the new fuel additive is a good idea anyway )and keep the oil changed regularly.

------------Robert

 

[70Post455]

Thanks for all the feedback. I would use mine for some daily drives also. I would/will use a good fuel additive and make sure the cooling system is up to date or correct.
I need to make up my mind on which truck. I am looking at a 1986 F350 ext cab 2wd automatic 6.9 flatbed setup with 169k miles on it for about $1800.00, very little to almost no rust since it was an inside the garage truck most of its life, but the paint is flaking on it some and the interior will need some work to be nice. I am not real hip on the flatbed, but I am sure I could sell it off and try to find a PU dually bed around.
I have also looked at a 1985 F250 2wd 6.9 with 180k standard cab manual in ok shape but needs a few leaks fixed, the gent is asking 2k, but will deal a little he said.
There is also a Very Nice 1987 F350 Crew Cab long box dually with a new topper, and very nice rear bumper and trailer tow pkg setup and new tires with 153k miles but no turbo for 4800.00. I would love to buy this setup, but I am not sure if this is more than I want to spend on my first diesel setup or go ahead and buy somthing this nice. I also felt this price was a little high but possibly this is the going price. This is a very nice looking truck.

TIA,
Tom

 

[Diesel JD]

Any of those trucks sound nice. When you go on your long tows, are you going by yourself or with the family/friends? A reg cab is great by yourself, but it sucks with more than one passenger especially with the manual! If you have a family and its a recreation rig the crew cab is probably what you want, as is the case with those who work on the road or something. 4800 is a little high for an 87 but if the truck is really great it might be worth it. The 87 represents the pinnacle of 6.9 improvements without the extra cavitation hazards of a 7.3. Also the 6.98 does have some tyrouble with head gaskets...has this one ever had new gaskets? It might be time soon....will you still be happy with that purchase if you have to fix the head gaskets? If it has the tow pkg and is a CC dually, it almost certainly has 4.10s. Not bad if you get the ZF5 or an aftermarket OD but the C6 with this setup will drain your diesel very quick! You'll still do better than a 460 but not by much, you'll get 10-13mpg, whereas wit the reg cab and T19 you'd be getting close to 20 with 3.55s on the highway and 15-16 even if it had 4.10s.

 

[Mr_Roboto]

I need to make up my mind on which truck. I am looking at a 1986 F350 ext cab 2wd automatic 6.9 flatbed setup with 169k miles on it for about $1800.00, very little to almost no rust since it was an inside the garage truck most of its life, but the paint is flaking on it some and the interior will need some work to be nice. I am not real hip on the flatbed, but I am sure I could sell it off and try to find a PU dually bed around.
TIA,
Tom

Most likely this is a cab / chassis with the narrower frame and a pickup bed will not fit. The wheelbases are different plus the C/C has the wheels much closer together.

Easy way - sight from in front of one of the front wheels. If the front wheel tracks BETWEEN the duals or towards the inside dual you have a pickup. If it tracks in front of the outside dual you have a C/C.

Also a C/C will say "Incomplete vehicle" on the VIN sticker.

 

[mechanoman]

Hi there, folks, I'm a newby to this site, but have over thirty years in the diesel engineering field. No, I'm not a know-it-all, but I can throw in my two cents worth now and then based on having written two diesel textbooks and wrenched on them back to the days of B-model Macks and starting Cat engines with pony engines.

About warm-up time. Pistons are not round when they are cold. Although it is just a few thousandths, they are deliberately oval shaped. Why? Because if you look into the bottom of a piston, you will see the bosses where the wrist pin goes through. When the piston warms up, these parts of the piston experience greater thermal expansion than the thin part of the piston. At normal operating temperature, the piston is theoretically round, but only after it comes up to temperature. This means that when the engine is cold, the piston has greater clearance across the wrist pin axis than across the opposing axis, which translates to greater blowby cold than when hot. That blowby contains plenty of "soot" from the combustion chamber on top of the piston, and it shortens the life of the engine oil. Diesels cool off when idling, and the old trucker's saw about "it's okay to let them idle all night" is not only baloney, it is actually illegal in most states.

The question is, is it better to warm it up in the driveway with a little blowby but a longer warmup time, or take a cold engine straight out on the road and subject the engine to more blowby because of increased pressure of driving vs. idling but with a quicker warmup time?

And yes, I am VERY interested in hearing what you guys think. After reading your posts since joining up, I am impressed with this site, and humbly thank all of you for letting me share your knowledge and experience. Diesel smoke on a frosty morning is one of the greatest smells in the world, and if they'd let me, I'd use #2 diesel fuel as aftershave! Thanks.

 

[Mr_Roboto]

Mechanoman, like you say diesels do not actually "warm up" at idle. The coolant gets warm from the combustion but the rest of the parts are relatively cold.

When I was a truck driver they had the tractors programmed to shut down after 3 minutes if you let them run on low idle without the clutch or brake depressed.

And my old 7.3 PSD would go to high idle if left in park for more than a few seconds when it was cold out.

I just let them run long enough to get oil to everything then start driving. Granted I don't put a hard load on the motor until it has warmed up and if someone lived next to the interstate I could see letting the motor warm up more on high idle.

 

[mechanoman]

Mr Roboto, I'm with you, once the oil is warm enough to have circulated throughout the valve train and the crankshaft, it is time to ease her out of the driveway for a little "light" driving until everything gets warmed up. My first two miles is through a 30 mph zone before I hit the highway every morning. Likewise, coming home each night I go through the same two-mile stretch at 30mph, which provides a nice cooldown for the engine. And the old diesel likes that routine a lot.