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Cause Of Low Temp Reading?


waf102

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I have a 90 Ls-400 (145,000 miles)

The temperature guage only operates between the first and second notch (on the bottom.) Most of the time it stays half way between them, but if running for a long time (3-4 hours) it works its way about 3/4 of the way to the second notch.

Had the thermostat replaced (it was a little "sluggish") and I have had the mechanics check the coolant temp - all is well. Mileage is great...no noticable problems. :D

Any suggestions on where to look next? (e.g. instrument cluster, some connection, sensor???)

I'd feel a lot more comfortable knowing what is going on temp-wise in my engine than just hope everything is fine :whistles:

Thanks!

Bill

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Mine only goes around the second notch too. I've been trying different things to see if they fixed it and nothing has so far....new OEM thermostat, coolant flush, tested the cluster needle itself. I just bought a new water temp sensor so hopefully that fixes it.

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FWIW, I had a similar problem with my Mercedes 300CE that ended catastrophically. The car began to run cool, not reaching operating temperature as it usually did. Normally the temp should run 85-90C but would run 80-85C. Sometimes on long downhills the temp would drop into the 70sC. In hindsight this was the thermostat beginning to fail in the open position. While driving one day, it finally broke in the closed position and the car overheated. It took me a couple of hours to get home as I would drive and stop, drive and stop. I took out the thermostat and the bridge was snapped in two. I believe this overheating episode soon led to my head gasket failing, a $1700 repair!

I would check the thermostat, you know the drill from typical repair manuals, i.e. boiling pot of water with suspendend thermostat and thermometer, or just try another thermostat.

glenmroe

1990 LS400

1991 MBZ 300CE

2000 MBZ C280

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Did the independent shop mechanic use an aftermarket thermostat and thermostat gasket? Nearly all of them do unless they are Toyota / Lexus specialty shops.

Yes...it was an aftermarket thermostat replacement. The problem had existed for a period of time before that. :unsure:

-B

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Mine only goes around the second notch too.  I've been trying different things to see if they fixed it and nothing has so far....new OEM thermostat, coolant flush, tested the cluster needle itself.  I just bought a new water temp sensor so hopefully that fixes it.

Let me know your results :)

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Uh oh, I'm getting worried now. My normal temp is right on the 2nd notch from the bottom. I've only had the car a couple of months, but that's where it sits all the time once warmed up. It warms up quickly, not slowly like Waf102. I was in 100 degree stop and go driving yesterday and it was perfectly steady at that temp, whatever it is. I did a flush a few weeks ago and I see no difference. I did a search, and it seems like just-below-halfway is normal for most drivers. A post by VGR suggested replacing the thermostat with an OEM one at 5 years (mine's a 98, 20K miles). What do you guys think about doing that? I'm sure it's never been replaced. Lexls, was your normal reading higher than 2 notches at an earlier time? Your site is very informative, by the way.

Waf102, that does sound a little low. You mentioned that the problem was there before the thermostat change. What was your normal temp? Good luck with it - I'm sorry I'm not much help.

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In todays paper I saw a 96 LS for sale. Curios I called him and told the guy a "friend" of mine was loooking for one. The car had 155k on it. Said the original owner drove it to Rolla ~130 miles everyday. He had a lot of repairs which surprised me. He said the car was "overheating" but he found out it was somehting to do with the elctrics. He had a chip replaced and now it seems fine. I dont know, anyone else experience this?

Thanks

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I wouldn't think that electrics would particularly cause overheating unless they weren't turning on the fan as needed. I haven't heard of buggy software in Lexus'. The cooling system itself is entirely mechanical, right? Water pump, radiator, mechanical thermostat. There are electrical sensors attached that influence the engine management computer and radiator cooling fan turn on/turn off. My bet is that bad water or coolant was used and the system is clogged, or the coolant was never changed, resulting in the same problem.

I got some clarification on the coolant gauge readings. I was thinking that midpoint up the gauge (3:00 position) was 3 notches up from the bottom. Therefore, those of us at 2 notches were pretty low. However, I noticed that midpoint is actually 2 1/2 notches. So those of us at 2 notches aren't all that low. Then I saw 2 photos on lexls' site that show the gauge at 2 notches, implying to me that that was normal (unless the cars aren't warmed up yet..hmm).

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In my experience the temp needle stays on the 2nd notch, or just a sliver above the 2nd notch on all 1st generation LS400's equipped with a factory original 180 degree F thermostat and thermostat gasket.

Since waf102's temp gauge stays between the 1st and 2nd notches his car might be

equipped with an aftermarket 160 or 170 degree thermostat or the thermostat may be stuck open. If it takes the temp gauge along time (more than 3 miles from a cold start) to reach the area between the 1st and 2nd notches, that would be another clue the thermostat is stuck open.

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I wouldn't think that electrics would particularly cause overheating unless they weren't turning on the fan as needed.  I haven't heard of buggy software in Lexus'. 

Have you heard about the problem with the 95LS' ECU?

98-00 Tranny software?

02+ Tranny software?

The list goes on..

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I wouldn't think that electrics would particularly cause overheating unless they weren't turning on the fan as needed.  I haven't heard of buggy software in Lexus'. 

Have you heard about the problem with the 95LS' ECU?

98-00 Tranny software?

02+ Tranny software?

The list goes on..

The temp should be in the middle. Maybe a little lower then the middle of the gauge.

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That's the interesting thing about temperature gauges in Japanese autos. It is the same in my Villager (Nissan) as in my Lexus. Once the car warms up, the temp needle goes up from cold and plants itself at a certain level and doesn't move, whether you are on the freeway or city traffic, on hills or with the AC on. The 2 Mercedes I have, the needle moves around in response to the same driving coditions.

glenmore

1990 LS400

1991 MBZ 300CE

2000 C280

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