2000LS400G

2000 Ls400 Platinum. 148,000 miles. The temp gage slowly goes up to just below red within 5 mins, longer if just in idle.
never goes above that. Drive 15 mins city streets, 15 mins on highway every morning. Does not matter how cold it is outside, still goes up the same.

1. Replaced Thermostat
2. Ac/heat works fine
3. Touched hoses and they are hot showing circulation.
4. Noticed smaller fan on front of radiator never goes on.
5. Put new fuse in yesterday.
6. Flushing system this weekend.
7. Thought about checking sensor behind bumper but not sure where it is or whether or not that effects the fan.
8. Big fan behind radiator kicks on right away everytime.
9. Check engine light goes on sometimes, but it is due to misfire and never mention of anything related to coolant.

Not a car guy so I learn as I go. Any help would be appreciated.

CLLEXUSS

There is a device that can tell the temperature of the hoses to make sure it is indeed running that warm if you are not sure. Maybe verify that first before putting a lot of money into it not knowing.

400fanboy

The secondary fan at the front, offset, which is electric is for the A\C and is only operated when needed.

My first two hardware thoughts would be water pump and cooling fan clutch (which controls the big fan behind the radiator). You say you're going to do a coolant flush - what is the condition of the fluid currently? Is it clean and filled appropriatley? If the coolant passes visual inspection, and there isn't air in the system, I would be wary about replacing it if you're going to just have to replace a lot of it again if the problem is actually the water pump.

Also worth making sure the serpentine belt is properly driving the water pump as well.

What's tricky to me is your heat still works properly, so that complicates things.

I'm at the end of my knowledge though. Those are my 2c & where I would look. Best of luck!

2000LS400G

Thnx for replies.

1. Heat went out yesterday and back in today.

2. My friend at work looked at it and said the clutch fan needs replaced and there is air in the coolant.

3. So therfore, going to replace clutch fan, clean up the throttle body as it idles low and sometimes flucuates up/down. Then replace belt, and finally flush coolant even though it looks good, yet never flushed before.

4. When I can afford it (live paycheck to paycheck). I am going to then do the timing belt kit/water pump. Water pump works that I know of.

Losiracer2

Check to see if the fins on your radiator are externally clogged with debris. I have an OH 99' LS400 and at 155k, my original radiator was about 60-70% blocked externally with road debris. I solved this by replacing the radiator.

I had recently moved to AZ at that time and in 105 degree temps while idling in the drive through, it would overheat and creep up in temperature and when driving, would slowly come back down to temp, and then go up again when idling.

400fanboy

1) The #1 thing to check is the coolant level\health.

2 &3) Do one thing at a time, if you get to the point where there is air in the coolant and the clutch fan is suspect, get the air out of the coolant first and see if that fixes your issues. Far cheaper, doesn't require replacing parts.

Start easy, work your way up. If a car won't start, you don't instantly pull the motor. You make sure there is gas in it. Is the battery charged?

What made your friend think the clutch fan was bad? The car needs to be completely cold to correctly diagnose it. It uses a viscous thermocouple, which grips the fan & makes it spin faster the hotter the engine gets, so it fails in very definite ways. It either locks up solid and spins all the time so it sounds like a semi-truck. Since you're having overheating issues, that isn't causing the overheating problem and can actually cause a motor to run too cool. Or it free-wheels and doesn't drive the cooling fan at all which can cause your problem.

> Spin the fan as hard as you can on an engine that has not been started that day.If the fan rotates more than five times, you can bet the clutch is bad. You should feel some resistance and the fan may spin up to three times, depending on the ambient temperature.

(side note: I put an aftermarket fan clutch on my car a few years back and it came out of the box locked up solid, always-on. replaced it with an OEM one and it worked fine. Note: I'm not sure if that was installer error and the shop bodged the fins of the temperature probe or what, if it was defective out of the box or that's just how it was supposed to work, but after the first 10 seconds you should never hear the cooling fan)

4) I'm not sure if we can rule out the water pump just yet. Did you check the serpentine belt & tensioner and the pulley on the water pump to make sure it's in working order? I could be something as simple as that.

timmy0tool

iTrader: (7)

do the simple things first: burp the air out of the coolant which is likely why the car is slightly overheating (common problem with air in the system) and intermittent heat.

i found that if you tilt the front end of the car up (like on a driveway or up on a jack), the bubbles will make their way to the front and out! you also have to hold the revs 1-2k for a 10-15 mins so the pump has time to push the bubbles out. lastly make sure you're heater is on full blast when bleeding/burping!