Like the title says, I installed a 180 degree thermostat and a drive belt and now it runs very rough, misses real bad and seems to be using a lot of gas.

I checked all my wires and vacuum lines, they all seemed good except the big line next to the map sensor on the TB was cracked. I replaced that and it made no difference.

I pulled and cleaned the tps and the map sensor but it made no difference, I haven't touched the iac yet, I might pull it off and clean it too.

I'm not sure what else to do at this point. I can't afford to just throw parts at it and I dang sure can't afford the lousy mechanics in this area.

It was running fine before it would start right up and seemed to idle good.

Any suggestions are welcome.

Btw: This is my daily driver, I have no other vehicles and I'm very uneasy driving it like this.

 

What year is your truck?

 

The first part I think I'd invest in...if you don't already have 1...is one of those cheap engine analyzers. You wanna get one that can read live data. Specifically fuel trims. You can get them from around 20-30 bucks. You'd be amazed how much you can tell about engine problems with things like fuel trims, engine coolant temp, intake air temp, etc. But, like moparman stated...the year is everything. Pre 96 means OBD1 n finding scanners that'll read those years...not so much.

 

Putting in a stat shouldn't change anything. Keep looking for anything you bumped like a ground wire.

 

Go back to the factory thermostat. You've got your truck stuck in "open loop" mode. Unless you flash the computer to run a cooler unit, your computer will inject extra fuel to warm the engine up. You don't have a choke, the computer handles that. For a daily driver you MUST run the 195 thermostat. Never, ever go with a cooler thermostat on ANY computer controlled engine. It will do exactly what you have going on now.

Also, don't get a "Failsafe" thermostat. EVERY one of those I've dealt with either had already failed or failed after installation. One time within a day. Just a plain factory thermostat will work just fine and the engine will run like it used to.

 

Sorry, I meant to include all that, it's a 2001 3.9l standard cab automatic. I've done all the standard bolt on upgrades, cold air intake, V8 tb, upgraded wires, cap, rotor, and coil, 1.7 roller rockers, sc tuner, all synthetic fluids throughout and a set headers that I haven't put on yet. The 180 thermostat was just part of the process, it gets hot here in Texas.

I've been seriously thinking about an analyzer, I didn't realize how cheap they had become until just recently. Any suggestions on which ones work best with a gen 2?

 

My thoughts also, that's why I'm asking for ideas.

 

Honestly, switching back to the old one was my next thought since it's the only thing that changed other than the drive belt. I had no idea about going an open loop, however, I did reset the computer by disconnecting the battery but it made no difference.

So I just went out to have another look at things and noticed an antifreeze leak, I now have a pinhole in my radiator. Very frustrated right now, I replaced the radiator a couple of years ago and I can't afford another one anytime soon. I hate to even ask because I hate adding anything to the radiator but any suggestions on stopping the leak?

 

A cooler thermostat won't help. Texas does not get to nearly 200 degrees. That's where your engine is designed to run. A lot of vehicles get tested in the desert with things done to make it even hotter. I talked to one Harley test rider who said when he was doing desert testing, it was a really uncomfortable feeling when he would hear the fuel between his legs in the tank boiling.

The new cap, rotor and wires are just good maintenance. A cold air intake will help a little, but you only have 6 cylinders and aren't towing a huge load so it may look cool at a car show, with your hood up, but it's working like the factory unit did with the same results. The 3.9 was well designed for what it was. All the first generation Magnums are based on the LA engine.

Ever since the late 1980's when fuel injection became common, people have tried to run a denser charge like on carbureted engines and they all lost fuel mileage. Some old hot rod tricks still work. A lower temperature thermostat isn't one of them.

 

I've always had good luck with "Aluma-seal". The plastic radiators today don't last long but this should plug the leak. It will usually last about a year or so. Open the radiator when cool then run the engine until the coolant is circulating. I'd make sure the heat is shut off so more stays in the radiator. Let it run for a bit then reinstall the radiator cap. This is if you are SURE it's the radiator. It might just be a loose clamp. You can put some UV dye to track the leak is you don't see the leak. UV kits are fairly cheap and handy to have around. Just make CERTAIN you use the yellow safety glasses as the UV light pen can damage your eyes.

I've seen people use "Barr's leak" but I've also seen it stop up heater cores. "Aluma-seal" is more temporary but works good. Now, if it keeps leaking, there IS an old hot rodder tick to make it last. Especially if the leak is at a seam where the plastic tanks meets the core. That is to loosen the radiator cap one notch. You will lose a little coolant and it will render your overflow tank redundant, but it will remove pressure from the system. You also won't have much heat in the winter. Make sure of what is leaking as it could be a loose clamp or the water pump is leaking from the weep hole underneath.