And you would be correct. The PCM does indeed compensate for engine temp, over a wide range. (after all, when you go out to your truck in the middle of january, and its -5*, gonna need a bit more gas for the cylinders to even consider firing...) Fuel ratio IS affected by coolant temp. No doubt about it. Now, once the truck goes into closed loop though, the Upstream O2 sensor has more control over it, than coolant temp. Is there some little algorithm in there, that the PCM uses to boost the mixture just a tad, even in closed loop though? I don't have an answer to that one.

 

I think it does spark knock a little when climbing a big hill with the a/c on. I usually just punch the o/d off button until after I've topped the hill. Which vaccum lines on the pass. side am I looking for?

 

I've used a 180 in my 96 over 5 years and the main difference I've seen is the engine temperature.
If a thermostat is working right it opens gradually, not cycling closed and open. The rating of it is the temperature starts to open, not the wide open position.

 

The thermostat starts to open at rated temperature, and coolant starts to flow. Eventually, coolant that is NOT 180* is going to make it to the thermostat, and it will close. The coolant then in the engine, heats up, thermo opens. Lather, rinse, repeat. It is not a constant flow system. Maybe in just the right circumstances it is, but, not as a general rule.

Remember, for cooling, change in temperature is directly proportional to difference in temperature. If you coolant is 180+ degrees, and it is 60 degrees outside, it is going to shed heat right quick, and will be well below the 180 threshold when it goes back into the engine. It can flow thru the engine faster than it can warm to 180* (again, given the 60 degree day...) so, the system WILL cycle.

If you are bored, and have the gas to waste, you can sit and watch it happen in your driveway. Take off the radiator cap, start the engine, and watch. The engine will warm up, you will be able to see coolant flow, the thermo will close, and flow will stop. And that cycle will continue as long as you stand there. Intervals will get shorter, and depending on outside temp, it may indeed reach steady state, where the thermo is constantly open a bit. I have no idea what temp that would be though. Would depend also on the condition of your fan, fan clutch, and water pump.

Keep in mind, coolant expands as it gets hotter, so, there will be some overflow while you watch.......

 

I guess the reason I have not seen a difference in my dakota with the same engine is because I gutted the cat (only has one O2 sensor) and opened up the air inlet with a ram air design and high flow air filter.

I have already done what I am willing to do for the inlet of air to the ram and have already put on a high flow cat. So I should be ok. But I am going to eventually take it one step further and put a glasspak on. And I know that the ignition system is going to work because I have the exact same components on my ram that are already tried and true on my dakota.

 

To shed some light on how the PCM system works, the temp is programmed into the unit as a parameter value measured in voltage output of the ECT sensor respective to the <SET POINT> value that is programmed into the PCM.

Now, after delving into this, what I found was, that depending on WHERE the vehicle was made (Canada, Mexico etc), that <SET POINT> ranges from 160-180ºF. There's a timer that is set for apx 3 minutes. The preset value programmed at the PCM for ECT must be met in order for the PCM to switch modes. So, as long as the ECT output value falls within the range, it will switch modes without issue. If it fails to meet that target set point, the PCM will not switch modes and, as a result, an OBD code will be set.

On my truck, it was made in Canada and, the OEM program was set to 160º. I had no issues with loop modes when running a 180-T-STAT on the OEM program.

On some trucks, the use of a lower T-Stat say, a 160º model, works without tripping a OBD code (engine cold for too long) while, on others where the set point is 180º, it trips the code almost immediately.

Operation and Function:

Now, the function of it opening sooner allows the coolant to thermally dissipate the heat by means of convection. In a stuck closed T-stat condition, it never opens thus, the coolant remains trapped inside the engine block absorbing all the heat until it reaches saturation. This is where, it can no longer absorb anymore heat and, it's at equilibrium where, becomes the same temp as the block which, as one knows, is not good.

The opposite can be said when stuck in the OPEN position. The coolant will continue to pass through the radiator. By means of convection, it will continue to dissipate heat to an extent as a function of it's use environment- which is, current air temp. This is why some experience no heat in the winter, there's little heat due to the fact that the water / coolant mixture is not able to absorb heat from the block due to being cooled almost immediately after passing through the block. So, whatever heat was absorbed is being dissipated as it passes through the radiator.

Now, in a hot climate, this is going to be less noticeable for, no one is going to be using the heater in the summer and, even if they were to turn the heater on, some amount heat would come out due to the ambient air temp would not dissipate heat as fast as in the winter so, one would feel heat and get a false sense that the system is ok despite it being otherwise.

Thought that may help some.

CM

 

Just looked up the OE thermostats for my two dodge 318 trucks....The '93 dakota calls for a 195....the 98 ram calls for a 192. I remember pulling these same thermostats out the first time. Are we sure that all rams were OEd with 195s?

 

That's a good question. Remember, that these T-stats are not precise so, they vary as far as at what temp they open or close. I believe the standard spec on OEM was ±5ºF.

CM

 

According to Autozone and Oreillys, any '98 dodge 1500 5.2 2wd gets a 192.

 

3* colder? I better go get a jacket, brrr...