Yet Another Engine Cooling Question!!

cayman

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OK. First, let me start by saying I have searched the forum over on cooling issues of the Viper. But I have yet to find any clues that explains my cooling issues.

I have a 1998 Roe SC'ed RT/10. 19,000 miles. Up until now, never had any cooling issues. Running a 160 degree thermostat, as suggested by Sean. Coolant system has been flushed every year and coolant replaced with 20/80 with 20% extended life coolant, one bottle of Water Wetter, and the rest distilled water. Normal temp at idle during the summer months (80 -90 outside) around 190 to 200. Recently, however, the temp at idle in 70 degree weather has been running almost to the first mark before 250. Fan motor kicks on and keeps the temp from further rising and will sometimes bring the temp down a little but not much. Once I get rolling, the temp comes back down to where it used to run. Although I'm not necessarily overheating yet, it concerns me because for this car, this is not the norm compared to what it has ran in the past couple of years. Things I've checked:
1. Coolant level both in the overflow bottle and in the filler tank. Up to level in both.
2. Fan operation. Kicks on when it's supposed to.
3. Radiator obstructions. None.

I assume the coolant system is working as it should based on the fact it cools down rapidly when rolling. One thing mentioned was air in the system. First, I haven't done anything that could have gotten air in to the system. And besides, what little air that could have gotten in it due to minute leaks, eventually work its way out after a few weeks without burping it? Also, if it had air and that's what was causing the hotter condition, wouldn't it run hotter than normal regardless of whether you were idling or rolling?

The only change I made prior to it running hotter is I swapped out the oil pan and gasket. The replacement pan was a new one made for a gen II. I don't know how this would have anything to do with the car running hotter, unless it, for whatever reason, has less oil flow? :(
Would the car running lean at idle cause it to run hotter at idle and not at speed? It just doesn't make sense that it's running warmer than usual at idle only, and not all the way through all operating speeds.:dunno:
 

Tom F&L GoR

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Just check or replace the radiator cap. The gaskets do harden in time and it does happen that hot fluid is pushed out to the overflow, but the leak allows air to get sucked in. Without doing anything, you get air in the system.

Your symptoms fit this - hot at idle, cooler when the engine speed is higher and airflow is high. If you get a new cap, get a spring center (the metal disc is spring loaded closed) and not a drop center (it dangles.)
 

CitySnake

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Recently, however, the temp at idle in 70 degree weather has been running almost to the first mark before 250. Fan motor kicks on and keeps the temp from further rising and will sometimes bring the temp down a little but not much.
2. Fan operation. Kicks on when it's supposed to.

Maybe I'm misunderstanding, but these 2 statements don't seem to reconcile. Your fans should come on around 190-200.
 

GR8_ASP

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I agree with Tom. It sounds like an air issue with air in the thermostat area preventing the thermostat from opening when it should, until vehicle movement gets the thermostat pellet within the hot coolant. This is sometimes called morning sickness. When that occurs the air is not discharged through the overflow system as the expansion has already occured. Try to manually burp the system and see if that changes the next drive cycle. If so then you need to locate the source of the leak. It could be external as Tom indicated or it could also be internal (head gasket compression related).
 

sirhc76

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same thing happened on my 96, the high speed fan relay was toast.
 

whitebluevipe

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same thing happened on my 96, the high speed fan relay was toast.
how many ohms of resistance should a fan relay be? i think mine maybe bad as well. i pulled the relay and test it with an ohm meter and it tests 67 ohm. but i don't know how many ohms it should be?
 
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cayman

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Fan relays check out fine. I manually shorted them out through the pin connector off of the pcm. I found this to be the best way as you are checking the wiring all the way from the pcm, through the relays and to the fan. Pin 2 goes to one side of the coil on the ON relay and pin 21 is for the HI/LO relay. Shorting out pin 2 to ground kicks the fan on low. Simultaneousy shorting that pin and pin 21 both to ground, will kick the fan on HI mode. BTW, you have to have the ignition switch on for the HI/LO relay to work as the other side of the coil on that relay is wired through the ignition B+.

CitySnake: The pcm grounds out one side of the coil to the ON relay at 207 degrees and then the HI/LO relay kicks the fan in to hi mode at 216, according to the service manual. I can only extrapolate the gage reading since its not linear and there are no corresponding temperature numbers for the hash mark between 190 and 250 but I have to assume that mark is around 205 to 210.

Also, for anyone else's tidbit info, there is only one temp sensor on the gen II's. The sensor has two elements. One feeds the temp gage and the other feeds a signal back to the pcm, which in turn, uses that signal to, among other things, turn the fan on low or hi based on the temp signal.

I will try the burp routine. I have the Roe upper radiator hose with the burp valve.
 
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Tom F&L GoR

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I have a Gen 1, so I can plead ignorance, but another thread I posted there are three temp sensors; gauge, PCM, and idiot light. Someone with a Gen 2 added that there are enough wires on the single temp sensor to still have a gauge, PCM and idiot light sensor.
 

GR8_ASP

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I believe there are only 2 sensor elements. That which is used to feed the non linear gauge display and the linear element for the PCM. In effect the gauge display tries to minimize needle movement around normal operating temperature while the PCM desires accurate temp sensing to provide for controls. The overtemp indicator should be driven by the PCM. That is the way regular cars in that era were created (starting with the 1994 2.0L). Prior to that there were 2 separate sensors.

Thus an accurate gauge reading does not indicate accurate PCM temp sensing or visa versa. PCM temp can be taken from the OBD port for Gen II.
 

ViperTony

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One of our GenII guys found a leak where the hoses slip on to the expansion/filler tank. A couple of worm clamps solved the problem for him.
 

viper k

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i have the same problem on my 1996 gts how do you manually burp the system
 

rsmitchell10

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Ok, another newbie type question. On my 01 RT the coolant bottle next to the oil dipstick is completely empty. I assume that's the overflow bottle? Where do I find the coolant filler tank that's referred to in the owner's manual? How do I tell if I need to add coolant/water and where does it go? Again, sorry for the basic questions.
 
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cayman

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One of our GenII guys found a leak where the hoses slip on to the expansion/filler tank. A couple of worm clamps solved the problem for him.

I was wondering about that. Mine seems to fit fairly tight but who knows. I'll throw a clamp around it.
 

dave6666

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Ok, another newbie type question. On my 01 RT the coolant bottle next to the oil dipstick is completely empty. I assume that's the overflow bottle? Where do I find the coolant filler tank that's referred to in the owner's manual? How do I tell if I need to add coolant/water and where does it go? Again, sorry for the basic questions.

The bottle you can see there with the hood up is empty??? You are WAY low on coolant then!

On how to fill the "other" bottle, the one in that fascia that you can't see, check the Illustrated Upgrades as I did a writeup with pics on that.

And like Tony mentioned above, get some hose clamps on that line from the bottle you can see to the bottle you can't see (pics once again in writeup). If it is leaking there every time the car heats up it will spit out coolant and every time it cools down it will **** in air at the leaking hose to the fascia bottle.

And make sure you keep the fascia bottle filled or then it will **** air regardless!

And finally, the fascia bottle is vented. Coolant will slowly evaporate from there. You should check that bottle a few times a year. More in hotter climates or if you scream around a track often.
 
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cayman

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Ok, another newbie type question. On my 01 RT the coolant bottle next to the oil dipstick is completely empty. I assume that's the overflow bottle? Where do I find the coolant filler tank that's referred to in the owner's manual? How do I tell if I need to add coolant/water and where does it go? Again, sorry for the basic questions.

The overflow bottle is in your front right fender well in front of the wheel. There is a slit that allows you to see where the coolant level is within the overflow bottle. I usually take a strong light, pop the rubber stopper off the fender skirt and shine the light down on top of that bottle. Makes it a little easier to see the level. The tank on top where you're talking about is the filler tank and if its empty, you need to fill it....quick! You may have already sucked some air in to your system by letting it get that low. Not a big issue, you just need to burp once you fill it back up. Then, you need to detach the rubber hose off the filler neck of that tank. and add coolant through a funnel until the overfill bottle below comes up to between the fill marks.
 

Tom F&L GoR

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I stand sort of corrected, but Gen 1 still one-ups Gen 2.

On the Gen 1, one of the three temperature units is actually a switch, not a sensor. The red idiot light that comes on with low oil pressure also comes on when a high temperature switch closes. The switch is separate from the sensor for the gauge, which is separate from the PCM sensor.

Aren't you glad I'm back to nit-pick? :D
 

Viper Specialty

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You may want to consider a PCM reflash to edit your fan temps. Kicking the fans on sooner tends to help heat issues- the fans have just enough power to keep the engine cool, but have a heck of a time pulling temps back down. Kick them on sooner, and they will at least remain static.

Personally, I would recomend a higher thermostat [you sure you dont have a 180, not a 160?] <190 degrees will lock adaptive updating, and can cause minor issues in driving if conditions change rapidly.
 

ViperGMC

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A buddy of mine had the same symptoms on his 96. I have a live OBD scanner and connected to the port and can read what the PCM is seeing. Cold, in the garage the water temp sensor said 50 deg above what the ambient air temp was. Obviously the sensor was reading high. A viper tech at VOI checked the car over and said that everything was fine but it was not. Changed the sensor and all was well.
 
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cayman

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You may want to consider a PCM reflash to edit your fan temps. Kicking the fans on sooner tends to help heat issues- the fans have just enough power to keep the engine cool, but have a heck of a time pulling temps back down. Kick them on sooner, and they will at least remain static.

Personally, I would recomend a higher thermostat [you sure you dont have a 180, not a 160?] <190 degrees will lock adaptive updating, and can cause minor issues in driving if conditions change rapidly.

I've actually contemplated shorting out the HI/LO fan relay so that when the pcm calls for the fan to come on, it does so in HI mode instead of low right off the bat. And yes. Its possible the thermostat is a 180 instead of 160. It was over two years ago when I installed the Roe supercharger, which is also when I swapped out the thermostat. Many *** and cokes ago!:beer:
 
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