LS1Tech... Another question for you

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Rick Shellenbarger

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Im still waiting on my new throttle body to arrive, however I noticed something today in regards to my high creeping idle while parked. It seems to be related to temperature.



I noticed that when I'm parked and idling, the idle rpms slowly climb from around 750 up to around 1000 rpm. This is one of the things that has been going on for awhile that has been a minor annoyance but not any real trouble. Anyway, I noticed that when its idling high like that, if I open the hood within 1 minute the idle returns to normal. Tested this several times today, every time the idle crept up I'd open the hood and it would return to normal...



So, I checked my coolant temps, just sitting there idling the temp peaked at around 208 (engine had been idling for about 20 minutes and its hot outside) degrees (via my SCT scanner reading the ECT), is that normal?



I haven't been losing coolant, and when I opened my radiator cap this morning after the truck sat all night, it was full to the top, but sometimes I can smell a faint antifreeze smell near the radiator cap... No white residue, just a faint smell.



Could the PCM be raising the idle to make the fan spin faster in an effort to cool the coolant? And if so, is this a normal thing or does it indicate that there is something wrong with my coolant system and/or PCM program? I had the radiator flushed by Ford at 90k, one year ago. the only other thing I've done is replace the thermostat when it went bad... And if I remember correctly, I think I replaced with a thermostat that opens sooner than stock, not sure on that though... 160 degrees maybe, 180.. Idk.



Anyway, the discovery here is that when my idle goes up, opening the hood makes it return to normal.



What do you think?



 
Just did another data log to verify the idle creep is temp dependent. The outside temp right now is 75 degrees. It took 25 minutes of idling for the RPMs to creep up to 980 RPMs, at that point the ECT was reading 206 degrees, the IAT was 180 degrees, cylinder head temp was 216 degrees, trans temp was 167 degrees, fuel rail temp was at 148 degrees, fuel rail pressure rose from 38psi to 55 psi, and the fan was on speed 3. At 25 minutes into the data log I opened the hood. Within 5 minutes idle returned to normal (around 730 RPMs) and the temps/sensors read as follows: ECT 204 degrees, IAT 128 degrees, cylinder head temp 214 degrees, trans temp 167 degrees, fuel rail temp 130 degrees, fuel rail pressure 40psi, and the fan kicked down to speed #2.



So it looks like the RPMs are creeping up with the IAT temps rather than the coolant temps. Might be normal, but it seems like things are too hot for sitting at idle in 75 degree weather.
 
I think that the thermostat is not functioning properly. I have never seen temps on my Trac above 200, even on very hot days and driving hard. ( I monitor the temp with the ScanGaugeII). I don't know the reasoning why you chose to go with a cooler thermostat but I would replace the one that is in there now.



I do think that you are right in thinking the PCM is increasing the RPM to move more coolant to try and keep everything from getting too hot.
 
I was thinking that if I went with a cooler thermostat it would open up sooner, allowing the coolant to keep the engine cooler... Do I have that theory wrong? If so I will change the thermostat tomorrow, lol.
 
First things first we have to remember that a thermostat, when functioning properly, is a minimum operating temperture limiting device in that the temperature should never fall below the thermostats set point. Installing a colder thermostat thaan what is recommended serves no purpose and in some cases can cause a check engine light to come on.



It is normal for engine idle to increase with temperature in order to help move more coolant and also to increase cooling fan speed when the pcm commands it to lock up. 208 is a long way from being too hot for an engine that has been idling that long.



On your SCT can you see what the fan clutch speed is and also the commanded fan clutch speed. It is possible that you may have a fan clutch that is not locking up properly and allowing the cooling system to get a little warm from it so thereofore the idle increases. What are your temps while running down the road?
 
I used to drive a '74 Ranchero with a modified 460. It ran hot the 1st couple of years when the engine was new. I tried installing a lower temp thermostat thinking that would lower the coolant temp, but it had the opposite effect and it actually ran hotter. I think, at least in my case, the thermostat was open most of the time and coolant was constantly circulating and didn't spend enough time in the radiator to cool down. Also, I think newer engines are designed to run in a more defined temp range than older engines, so I'd stick with the thermostat recommended by Ford.
 
I think you guys have hit the nail on the head. I'll switch out the Tstat this weekend. LS1Tech, I think youre probably right about the fan clutch not doing its job entirely, and that would make sense along with what I've datalogged so far. I'll see if I can check commanded fan speed, I didn't see it before in the option PIDs, but I'll look again. I know my scanner can read which speed the fan is running in, and it seems to work as designed, however I have had the roaring fan symptoms before, and although it's infrequent and normally seems to be working, the fan clutch is something I will pay more attention too. Maybe it's on its way out.



I have a bunch of parts coming in this week, so hopefully the weather plays nice this weekend and I can get everything done and datalogged for comparison.



I have the metal K&N intake tube currently, and I had to modify it when my filter was ruined on the road. I ended up cutting down the tube and adding a 4" coupler pipe and a larger filter (since the K&N filter that came with the kit isn't widely available for in the store purchasing), I suspect the larger diameter tubing and filter has effectively reduced the velocity of which air flows through the tube, reducing MAF count and allowing the IAT to get warmer while idling. I ordered the plastic intake tube and a new filter from K&N, it'll be interesting to compare the MAF counts ands IAT readings between the two setups. Also have 8 new injectors coming and a new throttle body. I believe 2 of my injectors are either sticking open or the orings have gone bad, as I can smell a fuel smell on two of my coil pack boots.



I cant complain too much about the Trac, I bought it used and I've put over 80k in a little over a year (I drive a lot for work). Most of the troubles I've had were either results of mods (ironing out tuning issues and such) or normal wear and tear items typical for where im at mileage wise.



I'll update this post with the results of a new Tstat, and the MAF/IAT comparison, and I'll keep a close eye on the fan clutch.



Thanks,



Rick
 
Well, I replaced the throttle body and injectors and re learned idle... No difference. I did notice something that sucks though, my coolant overflow tank is very low. I just checked the coolant level in the radiator a couple weeks ago, but I guess I didn't notice the overflow tank level.



It's about 3" below where it should be when cold and hot. No noticeable leak. I just changed my oil two weeks ago as well, no noticeable white froth/pasty look on dipstick but... Even though the oil looks nice and clean, it's a little high on the dip stick (above the top hole by a tad) when cold and it wasn't after the oil change... Im thinking that tomorrow when I open the drain plug I'm gonna get some coolant leaking out.



Hopefully it's a manifold leak and not a bad head gasket. When replacing the throttle body I could see some dry white spatter spots on the underside of the intake manifold... Sure would like to be able to spend my money on something other than repairs!



So I'll take it in to get looked at tomorrow I guess, again:(
 

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