Some possibilities:
Could your gage be off-calibration, and reading high? You might check that by
undoing the sensor and dropping it in a pan of hot water, using a good
thermometer in the pan for a reference point. See if the dash gage reads close
to the thermometer reading....
Another possibility: Modern thermostats are of amazingly bad quality.....I've
literally gone through three defective new ones in a row, right out of the box.
Their set points can be wrong, or (more commonly) they are "sticky" when new,
and open up too slow on occasion. Once I replaced the thermostat on my truck
after changing the water pump, a "while I was at it" kind of deal. Soon I
developed intermittent overheating, which made for a particularly bad nightmare
journey across southern Oklahoma. We tried everything to fix it, thinking we
had a blockage, or a collapsing hose, or just about anything else but a
thermostat -- since I'd just replaced that with a new one I ruled that out.
Finally in desperation I put the old thermostat back in, solving the
problem....Anyway, the condition you describe sounds like the thermostat is
working, but opening too late or not fully opening. If you get jerky readings
or fluctuations on your gage that's almost a sure indication of a sticky
thermostat.
Blockage causing reduced flow in the radiator is a possibility. I know you
just had it worked on and it should be good, but see above story on the new
thermostst... Or it could be a weak water pump, though that really doesn't fit
your symptoms exactly either....
Here's what I'd do -- the cheap/easy checks first. Try a new cap just to
eliminate that possibility....you could borrow a known good one from another
car for free. And try a 15 lb cap just to see, although I don't think the
cap's the problem. Next I'd either test the gage or replace the thermostat,
whichever is easiest for you. I really think it's one of those two things.
When changing the thermostat you could even install a gutted one to see how the
system behaves in open freeflow (but don't run it without at least a gutted
thermostat in place -- you can damage an engine with no restriction at all in
there). If it's not the cap, or the gage, or the thermostat, then it's time to
start looking at the radiator, the water pump, or blockages in the system
(blocked radiator, plugged water channels, collapsing hoses, etc.). I think
you'll solve it before you get that far, though.
Good Luck!
MD
--- "Gronberg, John" <john.gronberg@us.landisstaefa.com> wrote:
> Facts:
> Rebuilt vertical flow radiator. (new center section, "fins")
> New 7 LB radiator cap
> New 160 degree thermostat.
> 1275 engine.
> Antifreeze 25%water75%.
> Over the last winter I replaced the cooling components listed above. The
> two trips I have taken lately the water temperature from cold climbs
> steadily to about 212F then seems to back off to 200F. This is somewhat
> warmer than I am used to seeing. Any comments. I live in the Chicago area
> and it hasn't been that warm outside yet. I checked that the new cap is
> holding pressure and it is.
>
>
>
===
Michael B. Dietsche, P.E.
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