Operating temperature without thermostat.
 

Hi,

I think the previous owner of my Rally RX7 removed the thermostat to avoid overheating issues.

The problem is that now, in winter, the car will never get to operating temperature.

It is an 89 N/A, and after driving for an hour, I took the temperature at the upper and lower hoses of the radiator.
Both were about 150 degrees.

Am I correct to assume that the operating temperature of this model year should be around 180 degrees?

Also, the temperature gauge is only about 1/8th of an inch over the C.... when in summer is about a quarter way up.

I just wanted to know how much damage can be done with the car running at 150 degrees other than the incredible waste of fuel the car does.

Thanks.

I use the 180F thermostat. Some (whether they know it or not) use the 195F one. Either will work, but the 195F one will obviously run hotter than desired on high temp days.

Wont be doing much damage, but its not great.
Obviously if its not getting up to temp the thermosensor wont tell the ecu to change fuel mixture so you mileage wont be great.

As for the op temp your correct. 180~185f. I will say that if i temp my rad hoses they dont correspond with the actual temp that my aftermarket gauge is reading. They usually read anywhere between 120~160. If i temp just below the thermostat neck i get much higher reading at 170~180.

Im not too familiar with S5 but i believe 1/2 is op on your gauge. 1/4 would be for S4.

Did you actually remove the thermostat? The system needs some restriction. You can get a junk t-stat and weld or bolt it so it stays open, which will provide the necessary flow restriction to get the coolant hotter. You could also just put a properly functioning t-stat in and figure out why the car is overheating in the first place.

if you take out the thermostat you must block the bypass hole in the water pump housing that will elsewise kick back the hot water to engine and not pump ..

if this is done already ( usually a tapped 1/2 npt bung ) and run without thermostat the motor will take longer to warm and will equalise around 90 c with a natural ambience with the thermo bypass in the oil cooler

i ran in "MFR" mode for a few years, no drama .. and no you dont need a gutted thermostat

Thanks for the input.

Some comments/questions though.

I did not remove the thermostat. I believe the previous owner did because the car does not get up to temperature in winter.
We tend to do this on race cars to avoid the restrictions or malfunction of the thermostat at the track/rally. So we thought we would leave this one as is. But I do not believe it has any overheating issues (specially with the turbo hood on an N/A and the extra vents we did).

The problem is that it is so cold these days, (25-30 degrees) that the car does not get up to temperature. And I was wondering how bad would that be for the car.

Two questions now.

- Why does the coolant need a restriction? (open thermostat)
- What makes the car go into closed loop and adjust the fuel mixture?

Thx.

Mazda recommends gutting the thermostat but keeping it in place in race situations, and their stated reason is that some restriction is actually good and the cooling system performs better than having no restriction.

IT will never yield full power output because it will be in rich mode constantly. IT may also build up excess carbon on the rotors and spark plugs due to the rich mixture and low combustion chamber temperatures. If you still have catalytic converters then they are being destroyed and clogged each time you run the car this way.

Other than that, and the obvious poor heater function, it won't hurt the car at all.



Slowing down the flow of coolant gives it more time to warm up inside the block, which brings the engine to operating temperature as desired.


The coolant thermosensor located beside/behind the alternator. The ECU uses this to measure coolant temperature and adjust overall fuel mixture rich or lean as needed.

Ok.

Here is an update.

We opened the system and found out that the car did have a working thermostat. Either way, since we ordered one, we installed it anyways to make sure. (Both of them are 180 degree thermostats).

The car will still read 145 degrees at the top hose and 143 at the bottom one. Inside the shop! Which means that it was not at freezing temperatures.

I have driven the car on summer, and the needle was about 1/4 up. Now in winter is about 1/8 up.


Well. If both thermostats are supposed to let coolant flow at 180 degrees, but the coolant at the hose seems to be clearly cooler. Any ideas?

I am thinking that the coolant may just be flowing through the bypass people mentioned before. I am trying to find info on it, but I only find posts for FD cars...

Check your temp below the thermostat neck like savanna.seven says.

Maybe your gauge or your sender are bad. Hook up a mechanical temp gauge to rule that out.

I see no problem here. 1/4 reading on the gauge is perfect. It is normal to run cooler at a colder ambient temperature. What do you mean by "took the temperature"? With what? The neck will act as an insulator so you have to pop the radiator cap and measure the temp of the actual coolant.

Remember that heat rises so the higher points in the system will give you the highest temp reading so the lower section of the neck will be inaccurate. Or am I over thinking this?

Not on his S5, it isn't.
Should be around 1/2 normally, but all this talk of temps is useless until a real gauge is installed.

It is an 88. So I think its an S4.

Yeah, I have been looking for a temperature gauge, but I am still researching brands and the always troublesome electric vs mechanical gauge.

The temperatures were taken with a gun on the hose right after the thermostat housing at the top.

I know these guns are not 100% accurate. But It should not be 40 degrees off either....

Make up your mind.

It is an 88. But you know I cannot edit the first post anymore.

I forgot to write it on another post.

Yeah, I think I'm going to have to disagree with all of that.

The purpose of a thermostat is to keep a constant minimum operating temp regardless of ambient temp. So you should never be running less than the thermostat rating (after a full 10+ minute warmup).

I assume he is taking the temp by shooting the water pump with an IR thermometer. You can't accurately take the temp of plastic, rubber, or reflective metal (polished aluminum radiators, for example) surfaces, but the water pump/housing area just under the tstat neck gives accurate results in my experience.

Also, heat may rise in an ambient, non-contained, non-pressurized environment, but in a sealed pressurized cooling system the heat moves when the coolant moves, and the "hottest" part should be the area around the thermostat because that is where the hottest coolant is pumped prior to going out to the radiator to be cooled.

I have owned several s5 and the gauge has always been around 1/3. Give or take 1/16" or so for ambient temps.

I have never seen a properly operating s5 with a gauge that did not sit almost exactly in the middle. I mean, it may be "middle minus 1/16 of an inch" but it's pretty close. I'd say 1/3 or 1/4 indicates an issue on an S5.

make sure some chucklehead didn't lock the thermo fan clutch, that will keep the engine from reaching operating temp in winter(as well as suck up a huge chunk of power). if it is an S5 the gauge pops to the middle quickly and sits there from about 150 to 220 degrees. it is basically a dummy gauge unlike the series 4 gauge which will read the whole temperature spectrum and normally sits at 1/4 on the gauge at 180F.

improper timing can also keep the engine from reaching operating temps normally.

Can't he just disconnect the sensor...Ive read that the computer will default to 180 temp if it is not working or disconnected. At least so it wont constantly run rich

or he can fix it so the car will actually run properly in winter.

What manner of foolishness is this you are spreading? Logical thought is not permitted in this area of the forum, you'll have to go to the lounge for that. :lol:

That is what I am trying to do.

My reasoning tells me that if I get temperature on the hoses, it must mean that the thermostat is open. Which means the coolant should be at 180 degrees at least.

Could there be another way for the coolant to go on the other side of the thermostat without reaching temperature?

Is the heater core deleted?

Nope. Still there