running a little warm while on the freeway (1 Viewer)

[fishwater]

i have a '96 with a little over 230,000 miles. i got it when it had 90k on the ticker and have kept up with all the PM since then. i've recently (in the past 5000 miles) done my annual flush and fill of the coolant and changed to 10,000cst in my blue fan clutch. here's what i'm noticing:

on long highway/freeway runs at ~75mph (say for over 30 min)with the A/C on in 85 deg outside temps, i notice my coolant temp runs around 200-202 deg. it goes down quickly to ~195 when i turn the A/C off. it never gets above 195 in town or in stop-n-go traffic, it only gets to the 200 mark on long highway runs. i know it's not a huge deal, but i concerns me bcs last summer i don't ever remember seeing my temp getting above 198 no matter what conditions i was running in.

should i even worry about this? i'm thinking that i should replace the thermostat. any thoughts?

 

[mainemike]

The blessings and curse of a scangauge... I've noticed mine runs about 3-5 degrees warmer this season than it did last year. A little lower than yours, I'm usually at 195-198. But it used to run more around 188-193. I'm up to date with thermostat and PM, so what I'm suspecting is a slow decline in radiator efficiency (original rad). I have not done landtanks fan clutch mod, but it is a new fan clutch. One of these seasons I'll put in a new radiator and see what happens.

 

[fishwater]

thanks mike. i'm tempted to check my fan clutch setting too, but even if it's a little off, i would think it would make more of a difference on temps when i'm running around town and not so much when i'm running 75mph on the freeway. or is my thinking just way off? (probably is...)
i replaced my radiator about 18 months ago (had a small leak, but never ran hot).
i may just need to see if my radiator fins have crap on 'em.

 

[Downey]

Gents, keep in mind that there are "smog device" thermostats that do not let the engine run cooler than 220 degrees. Your water won't boil until it reaches 240 degrees, and then not when it's under pressure, and not when it's 1/2 antifreeze. I think your differences between 195 and 205 degrees whoudn't hardly show up on any scale, and wouldn't be much more than a flicker on a calibrated gauge??

 

[fishwater]

Gents, keep in mind that there are "smog device" thermostats that do not let the engine run cooler than 220 degrees. Your water won't boil until it reaches 240 degrees, and then not when it's under pressure, and not when it's 1/2 antifreeze. I think your differences between 195 and 205 degrees whoudn't hardly show up on any scale, and wouldn't be much more than a flicker on a calibrated gauge??

ahh....that's what i'm talking about!! i'm feeling better about it already (still gonna replace the t-stat, tho).

 

[mainemike]

I don't think the OEM thermostat is smog-devised, and the scanguage, being digital, does seem to be sensitive to 1 degree intervals. I agree that temps around 200 aren't cause for concern, but noticing that the system is consistently running hotter does suggest something could be done to make it run cooler, as it was doing last season.

 

[e9999]

I have said many times before here that IMHO some folks are inordinately worried about what seems to me to be perfectly OK temperatures. Temps in 190s and even 200s would not worry me in principle, depending on the driving conditions.

However, I'll say that if one does indeed see an increase in temp over a period of time, everything else the same -which is hard to ascertain- then that is something worth looking into. If the radiator were to, say, get slowly clogged up, I would want to know that.

Also, at least in my case, the temps are almost always lower on the freeway going at higher speeds than at low speeds in town (or on the trail of course). The opposite would seem a bit odd to me, and also perhaps a reason to look into things a bit.

 

[FirstToy]

the engine is most efficient around 200F so think of 200F as the prime temp and 190-210F as well within normal.

 

[fishwater]

Also, at least in my case, the temps are almost always lower on the freeway going at higher speeds than at low speeds in town (or on the trail of course). The opposite would seem a bit odd to me, and also perhaps a reason to look into things a bit.

thanks, e. that's exactly what had me puzzled, and why i posted. you would think that when you're in stop and go traffic, with less air movement through the radiator to dissipate heat, you would see an increase in coolant temps; not when you're running at highway speeds. can you think of what could be causing that to be the case? it shouldn't have anything to do with the fan clutch at those speeds, correct?

i noticed this (the increase in temps on the interstate) about 2 months ago after i did a scheduled radiator flush/fill. it had me concerned that maybe i had a blockage or something, so i emptied the system again and flushed it with distilled water with the heater wide open, dumped the water and repeated x 2 and didn't notice any sediment or deposits. i didn't open the drain on the block tho and i'm wondering if i should do that and use something like the prestone flush kit to back flush the system...

 

[e9999]

thanks, e. that's exactly what had me puzzled, and why i posted. you would think that when you're in stop and go traffic, with less air movement through the radiator to dissipate heat, you would see an increase in coolant temps; not when you're running at highway speeds. can you think of what could be causing that to be the case? it shouldn't have anything to do with the fan clutch at those speeds, correct?

i noticed this (the increase in temps on the interstate) about 2 months ago after i did a scheduled radiator flush/fill. it had me concerned that maybe i had a blockage or something, so i emptied the system again and flushed it with distilled water with the heater wide open, dumped the water and repeated x 2 and didn't notice any sediment or deposits. i didn't open the drain on the block tho and i'm wondering if i should do that and use something like the prestone flush kit to back flush the system...

well, I would think that the faster you go the less dependent you are on the fan. It's a bit tricky temperature wise, though, cuz you need more power to move the vehicle at higher speeds, but the engine efficiency can be better. And the pump (flow rate) only sees the rpm as main factor. So you could see lower temps at 3000 rpm in 3rd than at 2500 rpm in OD at the same speed if the friction losses in the engine are not much higher. Etc etc, hard to predict. But generally, I think I see lower temps on the freeway than in town.

I don't think you can do too much wrong by doing a good flush if you fill it back up with good coolant. Of course, there is always the possibility that you'd lift up some gunk and plug the rad with it, but that's not so likely if you do a lively flush and avoid sending the flush water from the block and heater into the rad.

 

[jlg32281]

Not sure if this is a common practice for people warm areas that rarely freeze and never freeze in the garage, but in the Supra world, many of us run a 90% distilled water, 10% anti-freeze, and water wetter (or similar product). Water is the best dissipator of heat. You need the additives in the anti-freeze for lubrication and the anti-corrosives, but water wetter gives you plenty of this to compensate for the lesser amount of anti-freeze. This usually results in a 15-20 degree drop in temps and one of the only ways to keep a Supra turbo from over heating. Anybody out there doing this? Comments?