J ust E mpty E very P ocket part 2

Okay, part two of my catch up post. After getting the fluids changed and leaks fixed that I wanted, I decided I wanted to take a look at the coolant system. Actually the temp gauge needle sweeping past 210 while waiting in a drive through prompted me to look at the coolant system.

So time to collect our data and try to reach conclusions about what might be going on...

• Going down the road temp is fine...actually seems to run cool. With the exception of the night I drove it home. It ran around 210 on the interstate.
• At idle it eventually goes above 210.
• Don't really notice much fluid movement at idle with cap off. Once at temp blip throttle and coolant moves.
• Top radiator hose never really gets hard or feels like it has water in it...but it must...
• Spin test of manual fan clutch shows fan harder to turn when cool than when warm.
• Elec fan never comes on.

So first thing I do is buy a new radiator cap as the old one looked rough. I'm pretty sure the old one wasn't holding any pressure. No difference made. Everything I've read points to the fan clutch. This makes sense if it's not turning fast enough as it gets warmer at idle it wouldn't move enough air.

From 1996 Jeep Cherokee

I was certainly hopeful when I saw the old clutch. It was certainly nasty enough to be causing a problem. Unfortunately no real difference. I can tell the fan is moving faster, it roars on cold startup like it's supposed to so I think it needed to be replaced, but it's not the root cause.

Next is the thermostat, technically this should have been first, but I just assumed it must be working since it runs cools down the road. I actually hypothesized it was sticking open and that was the reason it was running cool down the road, and hoped maybe it was stickign closed sometimes and causing it to run warm. So I get it out and find this...

From 1996 Jeep Cherokee

Not so much stuck open as cracked open, but definitely open. This explains why it runs cool going down the road. Also could explain the one time interstate warming if the parts got turned wrong and blocked water flow. But could it explain the heat at idle? Maybe if obstructing the slower water flow...nah, I'm not that lucky. So that leaves me with the following observations...

• By design the small fan that only covers 1/2 of the 12" tall radiator isn't going to do the job by itself. The auxiliary fan is needed at idle and it isn't kicking on when it should...
• Gauge is off a bit and it's not actually getting up to 220 where the fan would kick on anyway, so that would mean a) the fan relay is fine and b) it's cooling "well enough" anyway.
• Water pump isn't effective at idle. He supposedly changed it recently... Giving some revs at idle does help a tiny bit, but not anything spectacular.
• Radiator has lost effectiveness, works okay with forced air at speed, but the fan at idle isn't moving enough air for the radiator working at lowered efficiency... So I could either a) try to flush or b) just go ahead and buy new 3 core radiator...

Took the kids for ice cream and observed the following.

• Thermostat working correctly while moving. Needle stays about 3 needle widths from 210, you can see it rise a little then fall as the thermostat opens.
• Waiting in the drive through, the temp started to rise. So I let it continue to rise a little and at around 4-5 needle widths past 210(apparently this is where 220 is), the electric fan kicks on and the temp drops back down to 210. Not sure how much lower it might have gotten cause I started moving again after that.

So that leaves us with the following.

• It's an airflow/cooling efficiency thing. While moving it cools fine, so the radiator isn't completely clogged. By design the manual fan only covers half of the radiator and the electric auxiliary covers the other half. Once the electric kicks in it will cool back down to 210, so that is working correctly.
• If it was 100 degrees outside I would just call it good and deal with it, but the ambient temp was closer to 60, so once it warms up I'm not sure the system will cope.
• I've found scum/buildup signs of previous bars-leak in the radiator, so I'm hoping there is scale buildup reducing efficiency that an over the counter cleaner can help with and that is what I'm going to attempt first.
• I'm also going to wire in an override switch on the electric fan as I would rather it kick in sooner and prevent the temp going to 220 instead of just cooling it back down.

These fixes/changes will be taking place this week and we'll head into summer and go from there. Fingers crossed.