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DieselSite 203* Thermostat, Ford (1996-03) 7.3L Power Stroke

203* is the temperature that Navistar designed the 7.3L to run at. This is the thermostat that was and still should be in every 7.3L Power Stroke.

Until 1996, all 7.3L Power Strokes that were manufactured used an International water pump and an International short stem 203* thermostat. In 1996, Ford changed to a lower degree 195* thermostat. They changed water pump designs at this time as well. The new pumps required the new long stem 195* thermostat in place of the short stem to properly seat the bypass disk. All 1996-2003 Ford 7.3L Power Stokes came equipped with a long stem 195* thermostat. Recently the factory replacement thermostat available at the parts counter changed to 192*. The DieselSite 203* uses the correctly sized t-stat with the correct temperature spring so that you no longer have to give up the benefits of running your vehicle where it were meant to run.

Diesels run most efficiently at approximately 200* or above. A factory equipped 192*/195* thermostat will maintain an operating temperature at approximately 165*-170*. The Power Stroke has such an efficient cooling system, that this low flow when the thermostat is slightly open is normally enough to keep the engine cool. The downfall to this is that the engine, when not under load, never begins to reach its optimal operating temperature. The 203* thermostat maintains a minimum operating temperature of 190*. This brings the operating temps up from as low as 170* to as high as 203* depending on the operating conditions of the truck. This is closer to the operating temperature range that is preferable for optimal efficiency.

When your engine is under load and is producing higher combustion temperatures the 203* will allow the engine to run even closer to its optimal operating temperature. If the truck is under load and reaches the 203o setting, the thermostat is then fully open. This means you are at the maximum coolant temperature that the truck will reach. Your maximum temperatures are only a few degrees higher than in stock configuration, but these are degrees that you want for better performance. The best benefits come when the same truck is under a light load and would have a hard time reaching this optimal temperature. As stated above, you will never reach this optimum temperature with the stock 195* thermostat. The end result of installing the 203* thermostat should be slightly better fuel economy, less smoke, and maybe a few extra "ponies" to go along with it.

Although International still uses a 203* thermostat in some applications and that thermostat is available at most auto parts stores, it is the wrong part for the 1996 - 2003 Power Stroke. DO NOT USE THE INTERNATIONAL VERSION! It has a shorter shaft and will not shut off the internal pump bypass. This will cause inaccurate coolant flow direction through the engine. The thermostat in the Power Stroke not only controls operating temperatures, but properly directs the flow of coolant through the engine. As the thermostat opens, it proportionally closes the bypass. With the thermostat fully open, the bypass is mostly closed, and vice versa. With the International (Pre-96 Ford) thermostat, this cannot be controlled properly because of the shorter bypass stem. The shorter stem of the IH (pre-96 Ford) thermostat allows the thermostat to be fully open while the bypass is fully open. This means the coolant can travel in any direction available, whatever direction it chooses. It can either travel through the radiator or simply make the shorter, less restrictive path back through the front of the engine. This will cause uncontrolled overheating in the back cylinders of the block, with absolutely no signs of danger showing on the water temperature gauge in the cab. It is possible that the back of the engine can have no coolant flow at all yet the thermometer in the outlet of the water pump shows all to be normal. Multiple things can happen at this point. Cylinders can seize, freeze plugs can fall out and other normal symptoms of an overheating engine may occur. Worst case is a blown motor.

You reach a higher optimum operating temperature safely, by using the DieselSite 203* thermostat with the long stem for bypass protection. They've combined the two units to bring you a safe alternative. Now you can have the optimal operating temperatures without risking the chance of uncontrolled overheating in the back cylinders of the block due to an uncontrolled bypass.

Warranty Information:
-90 days on manufacturing defects and workmanship only.
-There are no other warranties, written or implied.

Improperly or poorly maintained systems can lead to failures in thermostats. As with all cooling system modifications, a water temperature gauge is a highly important tool in monitoring the system. As with the OEM thermostat requirements, we recommend that you change your thermostat out once per year to insure proper functioning of the unit.
Pricing: $35.99
5 5 2


Question: Why do I want my truck to run warmer?

Answer: You want the engine oil/water temps to be warmer so you get a cleaner, more complete combustion. This can actually bring exhaust gas temperatures DOWN. Diesel ignites from heat of compression. The idea is to compress the air charge to build enough heat to light the fuel, but if it's fighting against a low engine heat, the fuel will ignite, but not as complete as if the cylinders were just a bit warmer. The more complete the combustion, the cooler the exhaust temperatures. Diesel fuel combustion tends to complete best at temps above 200*. An added benefit from using the 203o thermostat is better working cab heaters in the cold months. Another added benefit is better fuel economy. We have seen everywhere from 1-4mpg increases. This depends on climates, driving habits, etc. Even a modest .25 mpg increase will pay for the thermostat in a few miles.

Question: Will I need any other parts or o-rings to install the DieselSite 203* thermostat?

Answer: Each DieselSite 203* thermostat comes with a new o-ring. We recommend a new thermostat housing when installing a new thermostat, however it is not required. Many are rusted too badly to properly seal. We sell the OEM housings for 1994-1997 as well as the 1999-2003. We also offer a billet aluminum thermostat housing in several colors.

Question: What can I do to insure no leaks during the installation?

Answer: Be sure to start with a clean, very dry surface. Most installation errors are caused by those who did not wait for the surface to dry or they did not clean and dry it well before installing the thermostat. Although it is not needed if you start with a clean, dry surface you can use regular RTV sealant during the install.

Question: What temperature should I be seeing on the factory gauge in the cab after installation?

Answer: The factory temperature gauge is not a true temperature gauge in that it does not show actual temperature. It has three settings: cold, normal and overheating. Cold is when you first start it up. Normal is anything that the computer thinks is normal operating temperatures. This can range from 90o to 220*. Overheating is just that. The gauge is not designed for measuring your actual water temperature it is designed to tell you whether you are in the normal operating temperature or overheating. There is no in-between. With that in mind, the gauge on your dash may stay the same, may go up or may go down slightly. It is NOT an indication of what the thermostat is doing. If you want to know your actual water temperature, you must put in an aftermarket water temperature gauge.

Question: I have a 1995 Power Stroke and it looks like I have a long stem style thermostat in my water pump. Is this possible?

Answer: Yes. If you've had your water pump replaced, chances are the installer replaced it with a newer style pump which uses the longer stem 195* thermostat. If that is the case, this 203* thermostat is the correct replacement for that style. *If you have a pre-1996 vehicle this is not the thermostat for your truck unless you changed to a later year water pump.

Question: Does the thermostat affect my engine oil temperatures as well as the coolant temperatures?

Answer: Yes it does. In fact, that is the whole point. It raises engine oil temperatures proportionate to the coolant temperatures. The engine monitors oil temperatures and our thermostat does not raise the oil temperature out of the normal acceptable range. It only raises it to a more desirable range for the diesel engine.



Shipping Information

  • Item Requires Shipping
  • 0.2 lbs.
  • W4.0000” x H4.0000” x L4.0000”

Customer Reviews

Comment Total Reviews (2)

not noticeable
  • Currently 4/5 Stars

Reviewed by:

Product ownership: Less than 1 month

Not purchased from: KT Performance

i have installed this and yet to notice anything or any improvements on my truck with this will update if i do notice

night and day difference
  • Currently 5/5 Stars

Reviewed by:

Product ownership: Less than 1 week

Purchased from: KT Performance

ive got a little bit of work i have done to my 97 7.3 (stage 1.5 injectors, swamps idm, 4 inch downpipe, custom tuning done by me, afe cold air intake.) i always thought it got up pretty decent, i put this t stat in and wow did it wake that thing up , turbo doesnt lag and not near as much smoke output, seems like its getting a little better miles per gallon as well, when i step into it she lights up and goes! i would recommend this to any one with a 97 or newer 7.3 with a few mods

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