Stock cooling system - interesting behiavor.
05-16-2017, 08:01 PM
#1
CF Veteran
Thread Starter
Stock cooling system - interesting behiavor.
Not even sure if this is a problem, I've just seen it enough times that I want to ask about it.
I have a stock cooling system, that for the most part appears to be in proper working order. I don't have any general temperature or cooling issues. I run real-time data so I can see my ECT temperature readings at all times.
Last night, I sat at engine idle (eating) for about 10-15 minutes while monitoring the numbers. It sat at 210f for that time, then slowly started to increment up until it reached about 221f and kicked on the electric fan. After about 2 minutes the electric fan had brought it back down to exactly 210f again. It then idled for another 10-15 minutes at exactly 210f with no changes. Then I drove off, uneventfully.
The behavior isn't new, and I've observed it over the last 2 years. It doesn't happen all the time, and seems slightly more prone to happen during the warmer months, though I've seen in cooler weather as well.
I've considered the possibility that the thermostat is closing down a little and failing to open a little as the temperature rises, but that doesn't seem to explain the electric fan being able to bring it right back down to 210f (and then stays there).
The system is thoroughly burped (with a burping funnel, and plenty of time, and with an elevated front end, last time I serviced the system). I have no indications that there is air in the system. The radiator cap is a relatively new Mopar cap, with no obvious indications that it is having any type of problem. Certainly no major temperature fluctuations when driving.
The only other thing I could think of is the viscous fan clutch every once in a while not doing its job, and then self correcting as the temperature comes up. Is this the most likely? Its original I believe, and I have about 75k miles on the vehicle.
I have a stock cooling system, that for the most part appears to be in proper working order. I don't have any general temperature or cooling issues. I run real-time data so I can see my ECT temperature readings at all times.
Last night, I sat at engine idle (eating) for about 10-15 minutes while monitoring the numbers. It sat at 210f for that time, then slowly started to increment up until it reached about 221f and kicked on the electric fan. After about 2 minutes the electric fan had brought it back down to exactly 210f again. It then idled for another 10-15 minutes at exactly 210f with no changes. Then I drove off, uneventfully.
The behavior isn't new, and I've observed it over the last 2 years. It doesn't happen all the time, and seems slightly more prone to happen during the warmer months, though I've seen in cooler weather as well.
I've considered the possibility that the thermostat is closing down a little and failing to open a little as the temperature rises, but that doesn't seem to explain the electric fan being able to bring it right back down to 210f (and then stays there).
The system is thoroughly burped (with a burping funnel, and plenty of time, and with an elevated front end, last time I serviced the system). I have no indications that there is air in the system. The radiator cap is a relatively new Mopar cap, with no obvious indications that it is having any type of problem. Certainly no major temperature fluctuations when driving.
The only other thing I could think of is the viscous fan clutch every once in a while not doing its job, and then self correcting as the temperature comes up. Is this the most likely? Its original I believe, and I have about 75k miles on the vehicle.
05-16-2017, 09:24 PM
#3
CF Veteran
Join Date: May 2012
Location: Lost in the wilds of Virginia
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Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
Yeah, it's probably the fan clutch. But idling is hard on any engine. I wouldn't be too concerned, but if it bothers you, it's not a difficult or expensive replacement.