engine cooling temp sensor

Hello everyone,
I have a 1997 2500 dodge ram, 5.9 engine. resently my gas mileage has dropped from 15 mpg to around 10 mpg, a local machanic told me it could be the ECT sensor. I decided to change out the sensor just to see if he's right but I'm having problems locating it. The one sensor I found was next to the top radiator hose under the alternator but only has 1 wire, doing a search- ect sensors are suppose to have 2 wires , can someone please tell me where the ect is located or on this model did the ect only come with 1 wire?

Thank you very much for any help

Bladesmith

See if this helps you out. If you don't have the two senders someone might have put a newer intake on it.

Gotta remember Merc, 97 was a weird transition year. Some 97's will have the 2 sensors, others may only have one.

Thank you Merc 225hp. that's it, a 2 wire sensor sitting just barely to the left side of the AC pump, looks like its going to be a nightmare to get to but at least I know which one to replace.

Another question, can it be bad and be causing problems with MPG and not trip the check engine light?

Thanks again

Bladesmith

You can change it but I doubt it will help one bit. I think it would be a cel for engine not getting up to opt temp, or engine to cold something like that. I would do a basic tune if not done already, front 02 sensor (NTK brand please), fix the plenum gasket.

But before you spend a penny get your mech to do a comp test or a leak down test, Lets make sure the motor is up to ***** first. He/she won't like it but have them start with cyld 8.

Hi Merc225hp,

Done everything you mentioned, last fall mpg dropped and engine began using oil badly, did a vacuum test and figured plenum gasket was bad, replaced plenum plate and gasket (it was bad), that took care of the oil usage problem but MPG still bad. Replaced plugs, wires, rotor cap, bug, O2 sensor with no help. So after talking with a mechanic he mentioned the ect sensor, said he had seen several chevy's with bad mpg because of a bad ect so he figured it might be the problem with the dodge. I'm the only owner this trucks had and I've kept it serviced to a T, with only 99K on it I figured it had to be something simple since the MPG fell off all of a sudden like the plenum problem, but who knows. I pulled a compression test on it last fall when I was searching for the plenum problem, I can't remember the exact readings but I do remember they were all within 10 pounds of each other.

Thanks again,

Bladesmith

Both the ect and the iat and the rear 02 play a part in fuel trim, thats a big drop off mpg wise. They are not that much cost wise so might as well change them both. But use Mopar parts please these trucks are fussy about those kind of things. What brand 02 was put in it?

Also a org owner here.

Edit: Did you change out the cat after the plenum work was done?

Thanks merc 225hp, I only replaced the front O2 sensor and I don't remember the brand, picked it up at the local auto parts store, but MPG was bad before so the O2 didn't have any effect. I'll replace the rear O2 and the ect and see if that helps things out. I know the MPG drop was significant and I keep getting reminded of it every time I gas up.

No on the changing of the cat.

The ECS, engine coolant sensor is an important part. The pcm (computer) uses it to regulate all the other engine functions. All engines are programmed to run rich when cold. this replaces the old "choke". If the ECS always tells the pcm the engine is "cold" then the pcm will always run the engine "rich". Giving poor mileage. A good scanner can read the ECS's output and see if it true. Running the engine "rich" all the time can lead to increased ring wear, poor mileage, and clogging of the catalytic convertor.

Bladesmith said:

Thanks merc 225hp, I only replaced the front O2 sensor and I don't remember the brand, picked it up at the local auto parts store, but MPG was bad before so the O2 didn't have any effect. I'll replace the rear O2 and the ect and see if that helps things out. I know the MPG drop was significant and I keep getting reminded of it every time I gas up.

No on the changing of the cat.

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wingnut said:

The ECS, engine coolant sensor is an important part. The pcm (computer) uses it to regulate all the other engine functions. All engines are programmed to run rich when cold. this replaces the old "choke". If the ECS always tells the pcm the engine is "cold" then the pcm will always run the engine "rich". Giving poor mileage. A good scanner can read the ECS's output and see if it true. Running the engine "rich" all the time can lead to increased ring wear, poor mileage, and clogging of the catalytic convertor.

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This. You need to replace the cat, burning all that oil would have helped clog it as well. Its really something that should have been changed when ya did the plenum gasket.

Thank you wingnut and Johnn123, I got unexpected busy right after my last post and haven't had time to mess with it. I'm hoping to get back to it this next week. Can the local auto repair do a exhaust test to see if the cat is blocked before I go to the expense of replacing it. Thanks again.

Bladesmith

Bladesmith said:

Thank you wingnut and Johnn123, I got unexpected busy right after my last post and haven't had time to mess with it. I'm hoping to get back to it this next week. Can the local auto repair do a exhaust test to see if the cat is blocked before I go to the expense of replacing it. Thanks again.

Bladesmith

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Even better you can. Unplug your front o2 sensor, then the remove it from the exhaust and go for a drive. See how she feels, any improvement you need a new cat, no improvement thats not your issue. Please be sure to disconnect it from the electrical connectors.

Hi Johnn123,

Just to make sure I understand what your saying, I should just unplug the wiring on the front O2 sensor then unscrew it and remove completely. I don't need to disconnect the O2 wires from the engine anywhere? Then with the O2 sensor hole empty drive the truck and see if its doing what? Just to make things clear, the truck doesn't seem to have any misses or rough idling at this time. So if the cat is needing replacement should there be a real notice to the engine performance and in what way?

Thank you again,

Bladesmith

Yes just remove the sensor completely. You do need to disconnect the wires, be sure to do that. Your pcm will have a heart attack if ya don't haha. The symptoms you are describing point to a clogged cat misses and such would be from a VERY clogged cat and other stuff needing maintenance. If the cat is need replacing, what its doing clogged is making it harder for the engine to push the exhaust gasses out. Unplugging and removing the sensor for the test will allow the gasses an easy exit. If it is in need of replacing, you will notice a big difference in the way the truck accelerates, idles, runs in general. Keeping it clogged can and will lead to cracked heads eventually, then your looking into some serious dough to replace them. Hope that helps!

Unplug the 02, remove it from the pipe, plug it back into the harness, zip tie it up somewhere safe go for a quick test drive, see if it behaves any differently. Any type of improvement means the cat is suspect and should be replaced.