This is the first diesel I've owned, so I need some advice. It has 221,000 miles on it, only about 10,000 put on by me. Whenever I pull a trailer at highway speeds, it overheats--worse when loaded, but sometimes even when empty. It has an aftermarket high-performance air filter (Airaid) which was in bad shape so I replaced it. The water pump was replaced recently. The radiator looks clean and I have blown it out with compressed air. It has one of those high-performance chips in it. Is there anything in the fuel-air injection system that could be causing this? When it shifts down on a hard pull, it puts out black smoke. There's nothing obvious wrong with the cooling system. I suppose the radiator could be plugged internally, but the coolant looks clean enough. I'd hate to pay to have the radiator removed and cleaned if the problem is elsewhere. Any ideas?

Ford recommends changing antifreeze at 45/75/105,000 miles and every 30,000 miles thereafter.

Total Capacity: 32 qts. Use 50/50 mixture of distilled water and Ford Premium Green Antifreeze (Ford Spec. ESE-M97-B44-A). Add Supplemental Coolant Additive FW-16 (8-10 oz. every 15,000 miles). Use Fleetguard test strips. Disconnect batteries and remove 2 hex-head engine drain plugs. One is above starter and one is on driver's side. Rear two cylinders are prone to cavitation. Use Ford Premium Green VC-5 antifreeze.
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Let me begin by saying that one of the most important items to maintain on a diesel is the cooling system. To do otherwise is to court disaster by greatly shortening engine life. Cavitation holes in the cylinder walls will develop in any diesel engine not properly maintained, resulting in an expensive rebuild. It's imperative to change the antifreeze at least as frequently as recommended by Ford. It's also imperative to add Supplemental Coolant Additive (SCA) and use test strips. Remember to remove the 2 hex-head engine drain plugs, in order to properly drain the block. Using compressed air is dangerous to the radiator and not recommended. My hunch is that your cooling problem is related to a blocked radiator, which probably should be replaced. You could try and remove the radiator and have it roded. Only use a 50/50 mixture of the specified antifreeze and distilled water. Radiator blockage frequently comes from tap water mineral buildup. Another possible explanation is a problem with the turbo. I would focus on the radiator first, however.

A friend of mine has a 1999 F-350 7.3L PSD 4x4. It pulls 13 head of cattle (6.5 tons) to market in 100 degree weather and never overheats. It's the finest truck I have ever worked on. I recently dropped and cleaned the transmission pan, installed a new filter, drained the converter, and refilled with 17.5 qts of Mobil 1 Synthetic Multi-Vehicle ATF. I also bled the whole brake system, using Valvoline SynPower Brake Fluid.

Consider installing an Amsoil bypass oil filter, using Amsoil 15W-40, performing regular used oil analysis (UOA), and greatly extending the oil change interval. It will greatly increase engine protection and allow it to run somewhat cooler. Poke a hole in bottom of the old filter to drain. Those Motorcraft FL-1995 filters are heavy, when filled with oil. You have a awesome truck that should last many, many miles, if properly maintained.

Thanks for the pointers. A lot of this is news to me. Several questions:

1. Does the coolant need to be replaced periodically because its molecular structure changes in ways that degrade its ability to transfer heat, or does it become corrosive, or what?

2. What do Fleetguard test strips actually measure? How often should they be used?

3. Is there any way to test whether the radiator is plugged short of removing it and having it rodded? If it is plugged, would I be better off just putting in a new core? About how much cost difference should I expect for replacement vs. rodding and reassembly?

4. How about the turbo? Is there a way to test its performance short of a rebuild?

5. What's the difference/advantage of the Amsoil bypass oil filter? What does "bypass" mean in this context?

6. Where do I get a used oil analysis done? Is there a do-it-yourself test kit, or do I have to take a sample and send it somewhere, or do most mechanics have the ability do one?

I don't do my own mechanic work, but I like to have some idea what's possible or likely before I take it in. Thanks for your input. I'll try not to wear out my welcome.

1. Antifreeze needs to be replaced because it no longer is able to protect the engine and radiator from the highly corrosive effects of a high temperature system. Chemical reactions step up with heat and the oxygen molecules in the water tend to become extremely corrosive. Antifreeze coats internal parts with silicates and other anti-rust chemicals to prevent oxidation. The inherent shaking of a diesel engine causes entrapped gas bubbles to constantly collide against the cylinder walls and will eventually create holes in the liner, which destroys the engine block. The SCA helps counteract cavitation.
2. Fleetguard test strips test for pH, sulfates, and chlorides. They should be used about every 6 months.
3. Probably not. With 220,000 miles on the truck, I would be inclined to replace the radiator. You might want to check with a local Ford truck dealer and see what they recommend. When labor is factored into the equation, I don't think the price of replacement will be much more.
4. A diesel mechanic can look at a turbo and tell if it's damaged or not. He can check for coking and damage to turbine blades, etc.
5. Amsoil bypass filters filter down to 1 micron. I would recommend you go to Amsoil.com and read about the product. Let me say that a diesel truck is the perfect application, as you will readily see. Amsoil and other labs perform used oil analyses. Diesels are perfect for this because your engine sump is 15 qts. Why discard perfectly fine oil, that is constantly filtered to 1 micron, if it's not necessary? Synthetics cost more initially, but save you a bundle over time in many ways. Many diesel truck owners, who use bypass filters and synthetic oil, will only change their oil every 100,000 miles or more. They do regularly replace full-flow and bypass filters, however. They are also getting their oil analyzed regularly.

I would also recommend you flush your power steering system and replace with Mobil 1 ATF. Power steering rack and gear assemblies fail from lack of simple preventive maintenance and are very expensive.

Same goes for rear differential fluid (Ford controlled slip). Ford Spec. WSL-M2C192-A and GL-5. Add 8 oz. of Friction Modifier (XL-3, Blue) first. Then, add 7.5 pts. 75W-140 GL-5 Synthetic. I would change differential fluid every 100,000 miles.

This is a very informative post. However, txgreasemonkey has created some confusion about how pinholes develop from the water jacket into the cylinder. The facts are that, on the compression stroke, the cylinder actually expands outward. When the pressure is release the cylinder wall retracts to it's at rest position very rapidly. When it does, small bubbles are created on the water jacket side of the cylinder.

This is the same as bubbles created by a boat's propeller running at high speed In the case of the boat, he explosion of these gas bubbles, slowly eats away at the trailing edge of the propeller. It is referred to as cavitation. In the case of the diesel engine, the explosion of those gas bubbles slowly eats away molecules of the metal wall of the cylinder. Eventually when enough metal erodes away, you end up with a pinhole from the water jacket into the cylinder. This is why this problem is also referred to as "cavitation" in a diesel engine. It has absolutely nothing to do with the shaking of the engine.

2001 F350 7.3l powerstrock.

Ok I'm a girl so I don't know about mechanic, so one day I was driving my truck until it overheated one of the hoses got loose and that's how it started. Now the motor makes a cranking noise like really loud I replace the belt the water house but I have no idea what it is...