temperature indicates that the engine is too hot. what are steps can I do to pin point the problem?

It could be the coolant temperature sensor, you'll need to find it, should be located either in the intake manifold or the block. You may need a manual to find this. Other possibilities include a faulty gauge (the gauges in the cluster can wear out over time), or a sticking thermostat. Have the cooling system pressure tested to check for internal leaks. You may want to have the coolant flushed as well, it's likely it may not have been done due to low mileage. Good luck, it will take some diagnosis time, but you should find the problem without a lot of trouble.

Thank you Litlehorn for your advice.

2/5 of the way up the gauge is NORMAL. Myself and other LS400 owners across various forums have found the same thing. I wouldn't worry about it unless it keeps you from sleeping at night, because it certainly isn't hurting your LS.

http://www.clublexus.com/forums/ls400/377171-diy-coolant-temperature-sensor-change-pics.html similar for you '98, some minor changes. same sensor. most likely either missing/low on coolant, due to cracked hoses, or a dead thermostat. or both.

2/5 of the hole range is totally normal temperature, actually many years ago whith mi first ls 400, i got a big crack on the plastic arround the fan behid the radiator, i don't remember it's name in english; & i took it out, them the temperature only took 1/2 of the way. Them the mecanic told me thas was not any problem for the engine, but the presure on the a/c sistem became too hig & that wass a reason for the car computer to decide open a valve & let the a/c gas come out avoiding other problems. If you wnt to confirm how much your temp gauge have to be indicaiting just go to a lexus shop, but try to find a small one, there is more oportunities to be raelly attended personali

You're fine. My 96 ES300 runs at 2/5th, and my 99 Pathfinder runs at 1/2.

NO NO NO, it is your water pump!! TRUST ME this is common

This sounds like a water pump problem that will need replacing, not immediately though but the next couple of months if you're to avoid something catastrophic. When my engine warms up the temperate gauge only as far as 1/2 and then comes down. As you explained, that's what the car manual says and anything otherwise would mean a potential problem. I have driven my LS400 a distance of 2,000 km and it never has it gone as high as 2/5. I'd recommend buying the water pump kit which includes the timing belt which should cost you no more than $150. Hope this helps.

i have replaced a water pump timing belt thermostat also bought sensors the one on the radiator and the one on the block by the intake my gauge still goes over half and my AC kicks off the last thing I'm doing to it is changing a radiator which I've already ordered I hope it will fix the problem how do I I don't know what else to do

Turn your ac on and see if your coolant fan comes on.