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Closed Thermostat: How much water should pass?

Started by wbdeford, September 26, 2016, 07:10:55 PM

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wbdeford

When the thermostat is closed, how much water should pass through?  I was filling my cooling system (58 SDV) with the upper hose disconnected and as the water level reached the thermostat, some water started passing it--enough that if I continued dumping water in the radiator, it would have overflowed the housing in just a few seconds.  Normal, or too much water getting by?
1958 Sedan de Ville

Past:
1956 Fleetwood 75 Sedan
1957 Fleetwood 60 Special
1958 Miller-Meteor Futura Landau Duplex
1960 Coupe de Ville
1966 De Ville Convertible
1970 De Ville Convertible
1971 Eldorado Convertible
1979 Sedan de Ville
1980 Seville

Scot Minesinger

When the thermostat is "closed" and the water pump is working same as if thermostat was open or closed, some water must pass through otherwise something would give, as you know.  The thermostat closed position does allow water to flow thru or bypass in a restricted volume so car can warm up and maintain temperature if it is too cold outside.  This restricted volume is unlikely to be specified in shop manual, although it could be.  You could heat the thermostat up and see if more (probably has to be hot to keep it open) water passes thru.  I have 1970 Cadillacs and of course they are different, treated this more as conceptual answer, hope it is useful.

If the thermostat is open too much, your temp gauge will let you know (never warms up), keep watch on it as fall weather settles in.  Likely this water fill test is not conclusive and you may be just fine.  Had a 72 Eldorado with an open failed thermostat and much below 75'F the car would not get past 160'F (had a temperature gauge on it).  Replaced it and car ran at proper temperature.

At least if it is open too much, you are unlikely to overheat until next summer.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

The Tassie Devil(le)

When the Thermostat is closed, you will get a dribble of water through it, as the idea of the thermostat is to close off 99% of the water flowing back to the radiator when the engine is cold, thus allowing a faster warm-up.

The Water pump is cycling the coolant through the engine, and when the coolant heats up to the required temperature, the Thermostat begins to slowly open, allowing a small amount of heated coolant to flow through the radiator to be cooled, then back into the engine, until the engine is sufficiently warm enough to operate.

One must remember that the thermostat is in a constant state of opening and closing as dictated by the temperature setting that is built into the thermostat.   It is this constant adjustment that maintains temperature over the whole driving range.

When filling a cooling system, it always takes time for the level in the radiator to stabilise, and sometimes a day before it is good enough to stop topping it up.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

TJ Hopland

Ya it wasn't till the 90's? when they started putting rubber gaskets on the thermostat's valve that they would actually seal up.   Apparently the reason they started sealing them is to get the engine to heat a few seconds faster which reduces emissions.    My observations is it makes the system very difficult to bleed when you do service and also gives you a check engine light when the rubber deteriorates.

   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

wbdeford

I know I am OK on the high end.....it's the low end I am concerned about.  The gauge used to peak at about the 1/4 mark.  Now, it doesn't get much above 1/8.  I heated the 180F thermostat in a pan of water on Saturday and it seemed to open and close correctly.  I used an infrared thermometer to track the temperature.

I used the same thermometer to measure the temperature of the thermostat housing while idling in my garage yesterday (air temp in the 60s), and also after a 10 mile drive to work this morning (air temp in the 50s).  Thermostat housing was in the mid 160s both times.  So, I am wondering if the thermostat is staying closed because enough water bypasses it to keep the engine cooler than its opening temperature.  Or, maybe the air cools the outside of the housing to mid 160s while it is 180 on the inside. 

I have a flush job coming up later this week (running cooling system cleaner in it for a few days)....will give me an opportunity to experiment a little.

Any thoughts on switching to a 195F thermostat? 
1958 Sedan de Ville

Past:
1956 Fleetwood 75 Sedan
1957 Fleetwood 60 Special
1958 Miller-Meteor Futura Landau Duplex
1960 Coupe de Ville
1966 De Ville Convertible
1970 De Ville Convertible
1971 Eldorado Convertible
1979 Sedan de Ville
1980 Seville

TJ Hopland

Most engines (I assume a 58 is included) have a bypass path for the coolant so even if the stat is closed there is still water circulating through the block and likely heater core.  The Oldsmobiles it was a an obvious external tube off the stat housing back to the water pump.   The 472-500 family it was in the block under the stat and used a special stat with a valve disc at the bottom that would close off that bypass passage when the stat was open for increased cooling under higher demand conditions.    I don't think it was common to have a feature like that, most of the time that bypass was always open so in theory there was always a percentage of water not going through the radiator.

Do you feel or read any significant temp in the upper hose before the stat temp?   If so you may have more than normal leakage.   If not you just have a cool engine and the air movement over the engine itself is enough to keep it cool under low demand and low ambient temp conditions.    I run into that fairly often with Olds engines, that bypass flows enough that the water never seems to get to stat temp till you get out and really work the engine.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

wbdeford

Pipes to the heater core are integral with the water pump.  As far as I can tell, there is no bypass at all.  There are four pipes attached to the front of the engine--the two lower ones through which the water pump forces water into the engine, and the two upper ones through which it returns.  The only way out, besides the heater core, is up through the thermostat.

I can grab and hold the upper hose as long as I want, unless I try to hold it way down by the thermostat.  (On my 71 with a 195F, I can't even hold it a full second.)  Will have to pay more attention to the hose and temps while the engine is warming up.

Thanks!
1958 Sedan de Ville

Past:
1956 Fleetwood 75 Sedan
1957 Fleetwood 60 Special
1958 Miller-Meteor Futura Landau Duplex
1960 Coupe de Ville
1966 De Ville Convertible
1970 De Ville Convertible
1971 Eldorado Convertible
1979 Sedan de Ville
1980 Seville

savemy67

Hello William,

Something does not make sense to me.  In one of your posts, you mentioned that you tested the thermostat and observed that it opened and closed correctly.  Did you measure the temperature of the water in the pan when the thermostat opened?

In your next post you mentioned that you can hold the upper radiator hose for as long as you want (except near the thermostat housing).  If your 180 degree thermostat is working correctly, I think that the coolant flowing through the upper radiator hose, and the hose itself, would be close to 180 degrees along the length of the hose.  You either have asbestos hands or perhaps the thermostat is opening at a lower temperature.  Without a measurement of the water in the pan when you tested the thermostat, it is difficult to know for certain if the thermostat is OK.  You may want to re-test the thermostat and measure the temperature at which it opens.

Respectfully submitted,
Christopher Winter
Christopher Winter
1967 Sedan DeVille hardtop

wbdeford

Yes, I used an infrared thermometer to measure the temperature of the water in the pan.  I used the same thermometer to check the engine temperature.

One thing I didn't take into account was that my cooling system was not completely full, so there was some air in the upper hose, which may have contributed to the lower temp where I was touching it.



1958 Sedan de Ville

Past:
1956 Fleetwood 75 Sedan
1957 Fleetwood 60 Special
1958 Miller-Meteor Futura Landau Duplex
1960 Coupe de Ville
1966 De Ville Convertible
1970 De Ville Convertible
1971 Eldorado Convertible
1979 Sedan de Ville
1980 Seville

DeVille68

Quote from: wbdeford on September 28, 2016, 07:16:49 AM
Yes, I used an infrared thermometer to measure the temperature of the water in the pan.  I used the same thermometer to check the engine temperature.
Hm..interesting. I don't quite believe that you got an accurate temperature reading.
I measured my thermostat but I had to use vegetable oil the be able to heat it up hot enough for the valve to open.

(because my sauce pan is not a closed pressure chamber, so you need some other liquid that will boil at a higher temperature. )
1968 Cadillac DeVille Convertible (silver pine green)

TJ Hopland

I have always tested them in water.   For every 500' of elevation you only drop 1 degree so 7500' you are only down to 198*F  which should still tell you if a 190* stat is opening or not.    Not a lot of places in the USA higher than that but if you were I suppose it could be a little more tricky. 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

CadillacRob

Direct from an old rad shop I town - if your thermostat doesn't already have a small hole in it, drill an 1/8" one.  This will help bleed air out of the system.  Be sure to run the car a good while with the cap off the rad to get all air out.
1950 series 61 sedan
1956 coupe de ville

59-in-pieces

I agree with Rob.
With a poppet thermostat - drill one to four 1/8 inch bypass hole(s) increases flow - easier to bleed
Have fun,
Steve B.
S. Butcher

DeVille68

Quote from: TJ Hopland on October 02, 2016, 01:15:48 PM
I have always tested them in water.   For every 500' of elevation you only drop 1 degree so 7500' you are only down to 198*F  which should still tell you if a 190* stat is opening or not.    Not a lot of places in the USA higher than that but if you were I suppose it could be a little more tricky.
Yeah you are right. Now, I remember why I had to use oil - I also tested the thermo vacuum switch for the ignition advance in one go. This one opens at 230°F.
1968 Cadillac DeVille Convertible (silver pine green)

TJ Hopland

I test those in a toaster oven.   First try was with a torch, that didn't work so well.  Hard to control and evenly distribute the heat, ended up melting all the plastic.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason