[Cloud9...68]

I'm pretty sure I know why - I bet the water just isn't getting hot enough to fully open the thermostat. It just so weird to see the gauge sitting at about 8:30 - 9:00 when it's in the 30s outside, while it stays comfortably in the 8:00 - 8:30 range when it's 100 degrees in the dead of summer. If anyone remembers my cooing system saga from a couple of years ago, I went through three thermostats before I found one that opened remotely where advertised. The one I finally stayed with had a stated opening temperature of 165 degrees (although when I tested it on the stovetop, which I realize isn't the most reliable test, it actually opened at around 180 degrees). But even this one obviously is staying too shut too long.

I don't see this as being a terribly serious problem, but has anybody else experienced this? Could anything else be causing it besides a sticking thermostat? The fans seem to be coming on at the ususal point, somewhere around 8:00, I think. Is it worth slogging through another gaggle of thermostats to find one that actually opens when it's supposed to? Am I just incredibly unlucky when it comes to finding a thermostat that works as advertised?

Partial Post: Please Login or Register to read the full post.

[flash]

when is the last time you bled the system? believe it or not, air gets in there - it's not truly a sealed system

when is the last time you replaced the reservoir cap? the rubber seal may have hardened, or the spring may have gotten weak - inadequate pressure will result in higher temps

also, the cycling of the system happens more when it is cold - the engine heats up to the thermostat point, and the "new coolant" is much colder in the winter than in the summer - the coolant on one side of the thermostat is much lower than the other side, acting as a heat sink, and the "cold soak" fakes out the thermostat so that it is actually well above the thermostat point on one side but the cold coolant on the other side drops the net temp of the thermostat down - this results in bigger swings of temp

phosphates and deposits also tend to stick to the core more during the winter, due to the colder temps - this results in capillaries being smaller and therefore less effective

Partial Post: Please Login or Register to read the full post.

[nissanite]

Just for reference ... I have had a water pump replaced in both 968's. I used Parts from the dealer (pricey but worth it). Both cars had the position of the gauge change to the same spot, just past the line into the normal range. They are consistent & always in the range under normal driving conditions in FL. Before the change, they would be in various positions when driving.

Partial Post: Please Login or Register to read the full post.

[Cloud9...68]

Thanks for the inputs. I could easily see my radiator cap being tired, and it's been nearly two years since I've bled it, so maybe there is some air in the system. With all the cooling problems I had in 2008, the system has been flushed so thoroughly that if ethelyne glycol weren't posionous, my coolant would be clean enough to drink. This, combined with the fact that I had my radiator rodded (the guy who did it said it was completely clean and free of any obstructions), tells me my cooling passages are probably nice and clean.

The real striking thing to me is the fact that it actually runs a tad hotter when it's very cold out, than when it's very hot. I've just never experienced this before. One thing I haven't done yet is put my hand on the return radiator hose after the engine is thoroughly warmed up. When I had the bad thermostat in spring 2008, this hose was room temperature, and when I finally got a working t-stat, the hose became blazing hot, as it should be. It's going to get very cold in the next couple of days, so I'll take it for a spin, and see if the hose is hot. I suspect it isn't. I'll decide what to do based on what I find.

Partial Post: Please Login or Register to read the full post.

[Cloud9...68]

Well, I finally got around the checking the temperature of the large return hose now that I've driven it during another cold snap - not only isn't it hot, it's downright cold to the touch. So, as I suspected, it's yet another bad thermostat! It was 3.0 degrees celcius (the interior temp gauge is stuck on celcius, but I guess that's in the high 30s farenheit) out today I was driving it, and the water temp gauge was well past 9 oclock. I don't know what it is with me and thermostats, but I think this is my fourth one in the last two years. At least it's not something really serious, like bearings or cylinder heads. Anybody else have this much trouble keeping a good thermostat? Any recommendations on brands, or do they all come from a common manufacturer? Thanks.

Partial Post: Please Login or Register to read the full post.

[flash]

i like stant, but i'd call pete

when you go to check it:

fill a pan with water (or better yet a 50/50 blend of coolant/water if you can convince the wife to let you destroy one of her pans)

using a good thermometer, heat the liquid to 150 degrees

suspend the thermostat over the pan and immerse it, but do not let it touch the pan (you can rig a string and hang it from something)

turn up the heat gradually

watch the thermostat

it should begin to open a few degrees before its setting point

hopefully it is just the thermostat, but you could have a pump problem though - don't assume a new pump is working either - we've seen them bad right out of the box

Partial Post: Please Login or Register to read the full post.

[stewhatch]

Pete changed my coolant reservoir cap last February when I last had my car at the Barn, and I could not believe the difference that small change made. My temp never goes over half even on the hottest of days. Perhaps that may solve your issue?

Partial Post: Please Login or Register to read the full post.

[flash]

yup - the pressure cap makes a huge difference in temps - it raises the boiling point - some coolant brands actually put a chart on the bottle of the effectiveness based on the pounds of pressure

the other benefit of a good cap is that the pressure forces air out of the system - if you have a weak cap, you may never get the system bled

Partial Post: Please Login or Register to read the full post.

[Cloud9...68]

Good suggestions - thanks. I'll give Pete a call, and follow Flash's recommendations on how to check the thermostat. I'm pretty sure the problem I'm having is rooted in the thermostat, because of ther coolant temperature's behavior in relation to the outside temperature. The coolant temperature gauge reading actually drops as the outside temperature goes up, indicating the ambient temperature is allowing the return water to heat up enough to finally open the thermostat. If it were a bad water pump, I wouldn't expect it to just run hot all the time, and actually be worse the hotter it is outside.

As far as the cap, yes, I'll get a new one as a general maintenance item, as mine is probably very old, and is probably not holding pressure as well as it should. Though again, I don't think a weak cap would be causing the peculiar inverse reaction to ambient temperature. I'll just order the cap and thermostat from Pete. Thanks again.

Partial Post: Please Login or Register to read the full post.

[Cloud9...68]

I just installed the new thermostat and cap I order from RS Barn - problem solved. I replaced the cap first and drove the car for a couple days to test the effect of the two separately. I'm sure the new cap was a good general meaintenace item, so I'm not sorry I replaced mine, but this didn't impact my particular problem - the car ran about the same, and significantly hotter than it should this time of year. But the new thermostat did the trick. By the way, has anyone priced antifreeze lately? I paid $16 for a gallon of the phosphate free stuff. Ouch!

Partial Post: Please Login or Register to read the full post.

[ds968]

LOL, I just posted a related "hot running" note on the turbo thread ; before I changed my OE switch to the lower temp one the car was always running very hot. Same radiator cap, same coolant, same flushed system, only the switch made a world of difference. And BTW, when driving in the rain the car was consistently running at it's hottest - I NEVER understood that, and no one was ever able to explain why..

Partial Post: Please Login or Register to read the full post.

[flash]

i have been painfully aware of the price of coolant lately - i changed it when i changed my upper hose due to belt wear as a result of the missing support clip - i then changed it again when i did the supercharger - i will have to change it again when i remove the new upper hose for duplication

each time i also go through a half bottle of water wetter, a gallon of distilled water, and a new drain plug

it adds up

Partial Post: Please Login or Register to read the full post.

[Cloud9...68]

"before I changed my OE switch to the lower temp one "

What's an OE switch?

Partial Post: Please Login or Register to read the full post.

[flash]

original equipment

Partial Post: Please Login or Register to read the full post.

[Cloud9...68]

Ah, of course. I figured it had to be the fan switch, but couldn't think of how "OE" could be an anacronym for it.

The pevious owner told me my car has a low temp fan switch, but I haven't been able to confirm that. When everything is right (functioning thermostat, good radiator cap, all hoses on tight, etc.), my car seems to run pretty weel, temperature-wise, but I wonder if the low temp switch makes it overly sensitive to perfect thermostat operation. The car seems to eat thermostats; it's a good thing they're so easy (if wasteful of antifreeze) to replace.

Partial Post: Please Login or Register to read the full post.