180° Thermostat Install


DML FAQ : HOWTO : 180° Thermostat Install

Note: This page documents the install of a 180 degree thermostat in a 1996 Dodge Dakota 318 Magnum with air conditioning. Other model years might be (but probably aren't) different; also if you don't have air conditioning, some steps outlined here aren't nescessary. (Namely, all of the steps involved in moving the generator out of the way in order to get at the thermostat.) Also, I have an open element air cleaner, which means that I don't have the plastic ducting from the grille to the air can. You may want to move that out of the way to make it easier for you to work.

This procedure is basically the same as the one outlined in the 1996 Factory Service Manual. A few other people have been able to change their thermostats with considerably less work. (See the bottom of this page for more info.)

First of all, why would you want to replace a perfectly good thermostat? Well, for a couple of reasons; to reduce pinging and increase power. After I installed my Mopar Performance PCM (computer), I was getting pinging, even with 93 octane. Headers will help in this regard, and so will a cooler thermostat. I needed the thermostat for the pinging, and even if I hadn't, I was going to change it anyway, just for the increased power.

The thermostat has one simple function; to stop engine coolant from flowing below a certain temperature, and to allow it to flow above a certain temperature. This allows an engine to heat up quickly. By blocking the coolant's path to the radiator, it won't cool, therefore it won't cool the engine either, so the engine heats up much more quickly. After operating temperature has been reached (determined by the thermostat), the coolant flows through the radiator and cools the engine. If the coolant drops below the required temperature, the thermostat will close again, and cause the engine to heat up until it has once again reached the proper temperature.

If you look inside your engine bay at the radiator, you will notice a large hose coming off the top of the radiator. This hose bends 90 degrees down, and goes right to the top of the engine. At the end of that hose is the thermostat. (The yellow arrow in Figure 3 is pointing to the approximate location of the thermostat.) Coolant flows up through that hose and into the top of the radiator. There is an easy way to see wether the thermostat is open or shut. While the engine is running, just feel that large hose. (Be careful of any jewelry or loose clothing which might get sucked into the serpentine belt right below the hose!!) It will become warm when the thermostat opens and allows the hot coolant to flow into the radiator.

So, how will a cooler thermostat give you more power? By allowing the coolant to flow at a cooler temperature than the stock thermostat, a replacement thermostat will keep the engine temperature cooler than stock. As we all know, cooler air is more dense and will make more power. Also, by keeping the pistons, heads, cylinder walls, etc. cooler, you will reduce or eliminate "hot spots", which could prematurely ignite the fuel and cause detonation and pinging.

As usual though, there is the law of diminishing marginal returns. If a little cooler is good, a lot cooler is even better, right? Nope. There is a reason for having the thermostat there in the first place. A cold engine isn't any better than a hot engine. There is an allowable range, and we want to be at the coolest end of that range without actually dropping out of it. Fellow DML'er Sean Meldrum informed me that according to some Chrysler technical manuals he was reading, the computer likes to see the engine hit 182 degrees. Any cooler than that might cause a problem and/or generate a trouble code.

The stock thermostat is rated for 195 degrees. We will be replacing that with a thermostat rated for 180 degrees, which is a common exchange for these trucks. Mopar Performance sells a 185 degree version also, I believe. Whatever the value, the install procedure is the same.

This isn't a difficult mod; you just have to remember to put everything back the way you found it and make sure that the only "extra" part left over is the old thermostat. :-) It isn't difficult, but it could be messy; draining the coolant can be something of a pain.

(Click on the pictures to see a 2x version)

Figure 1 The first thing to do is to make sure that you've got all the tools and parts that you need. (Most of which should be listed in the "requirements" section above.) Figure 1 shows the thermostat and gasket that I used. Both are made by Stant, part numbers 65358 and 27138, respectively. I just went down to the local Parts America and gave them the year, make, model, etc. of my truck and they looked up the appropriate thermostat for my truck. (Make sure that you get one cooler than 195 degrees, or this whole mod will be nothing but a waste of your time.) :-)

Parts America had two versions of the thermostat; normal and "heavy duty". The normal one was about $2.50, and the heavy duty was $5.00. The heavy duty one had a lifetime warrantee and was visibly better constructed than the cheaper version. Throwing caution to the wind, I recklessly splurged on this luxury item. You'll also need a gasket, which set me back an additional $.99. You will NOT be able to use the gasket that is on the truck now; bite the bullet and get the gasket too. As you can see, this is not one of the most expensive mods you can make. :-) Including the distilled water and the coolant, I spent a total of about $21. (A gallon of coolant is about the same price as the thermostat!) You can try to reduce the cost of this mod by saving the coolant that you drain out of the truck. Ha! Good luck! (More on that later.)) (Actually, a few people have done this mod without wasting any coolant at all; if you can do the same, the price of this mod is limited to the thermostat and the gasket alone.)

In order to remove the thermostat, we have to drain the coolant out of the system first. Let the engine cool down. If the coolant is hot or under pressure, you could really do a number on yourself. (Burns, objects being shot at you under pressure, etc.) Make sure that you have plenty of clearance underneath the truck. You will have to crawl around under there to drain coolant and remove some protective panels. Once you start, you won't be able to move the truck until you are done! I used a set of oil change ramps.

Note: Shortly after I did this write-up, I received a message from David Zavetsky (zavetsky@usaor.net) who said:

"I did my thermostat a few months back and found that I could avoid having to remove the alternator and the mount. By using a really long screwdriver, I was able to get to the return hose clamp by sneaking in through the opening in the bracket on thge side......Then, I could remove the bolts for the thermostat housing, pull it up off the engine and then remove the thermostat that way. Saves a lot of extra work."

Note 2: Sean Meldrum (spm@c3net.net) was able to change his thermostat without spilling a drop by using a cheap gas siphon to pump the coolant out of the radiator and the hose running to the thermostat into a clean milk jug. If you're not planning to replace all or part of your coolant, this might be a good way to go.

Note 3: Dewayne Blanco (dblanco@stdauto.com) said:

"I recently replaced my thermostat without removing anything but the hose from the radiator; using a long extension I unbolted the thermostat housing then removed it and the hose (with the god-forsaken clamp in place) in 10 minutes! Cleaning off the old gasket was not too bad, with a long large flat blade screwdriver...entire job took 30 minutes. Hope this is another alternative for someone who hates stupid clamps in inaccessible locations..."

Note 4: Ray Block (bpracing@worldnet.att.net) added the following tips:

  1. You don't have to remove that plastic shield beneath the radiator unless you want to capture/save the coolant. I can open the radiator drain from above and just spray the coolant off the shield when I'm done.
  2. It's not necessary to remove the block drain plugs unless you want to flush the entire system.
  3. I replaced the drain plug with a petcock on the passenger side. There wasn't enough clearance on the driver's side. Future draining will be quicker/easier.
  4. There's no need (on mine) to remove the support bracket. I loosen the end at the alternator and remove the bolt at the manifold end. Then just swing it aside.
  5. I did not find it necessary to remove the alternator. I loosened the lower bolt/nut and removed the upper bolt. Then just swing the alternator to the left, reinstall the bolt through the mounting bracket and let the alternator rest against it. Gave enough clearance on mine. Did not have to disconnect any wires either.
  6. As suggested in some other posts, the "Front" tab can be ground off to make future TS changes easier.

Contributed by: Jon Steiger, David Zavetsky, Sean Meldrum, Dewayne Blaco, Ray Block
Last updated: Mon Jul 21 20:55:37 2003