Will my car overheat without a thermostat?
11-07-05, 02:38 PM
#1
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Will my car overheat without a thermostat?
I am running no thermostat at all. Will that cause my car to overheat? Also, how do I know if my clutch in my fan is weak or bad? It doesnt seem to blow as hard as my past cars have, but it does still blow?
11-07-05, 02:55 PM
#2
Running with no thermostat prevents the water from staying in the radiator long enough, and will cause localized hot spots in the water cooling passages. Install a mazda OEM thermostat ASAP.
As far as the fan clutch.. At operating temperature the fan moves quite a bit of air. I have seen failing clutches that I could stop with a wrench (while the engine was running!). if your car is at operating temperature and that fan isnt moving much air, then its possible that the clutch is suspect.
Since you live in Abita Springs, can I get a 6-pack of Turbo Dog please!!
As far as the fan clutch.. At operating temperature the fan moves quite a bit of air. I have seen failing clutches that I could stop with a wrench (while the engine was running!). if your car is at operating temperature and that fan isnt moving much air, then its possible that the clutch is suspect.
Since you live in Abita Springs, can I get a 6-pack of Turbo Dog please!!
11-07-05, 03:10 PM
#3
Running with no thermostat may be OK for a short period, but it does mess with the coolant flow and can cause long-term problems.
If you really want to run with no thermostat (track car or such), "gut" an existing thermostat. If you cut out the center unit of the thermostat, it will flow like it's wide open, but the flanges will still allow for the correct coolant flow patterns.
The clutch fan should spin more or less freely until it gets hot, then tighten up. If the car isn't overheating in traffic, it's probably fine.
-=Russ=-
If you really want to run with no thermostat (track car or such), "gut" an existing thermostat. If you cut out the center unit of the thermostat, it will flow like it's wide open, but the flanges will still allow for the correct coolant flow patterns.
The clutch fan should spin more or less freely until it gets hot, then tighten up. If the car isn't overheating in traffic, it's probably fine.
-=Russ=-
11-07-05, 05:14 PM
#4
Senior Member
The T-stat does two things control temps, it also blocks the bypass valve with the flat disc when hot. When it is open and the t-stat is closed on start-up it makes the coolant recycle in the engine without going to the radiator so the car warms up quicker.
If you gut the t-stat, u will always be partially recycling hot coolant around the radiator.
If u must do something, put some small holes round the outer lip of the t-stat but, let the disc do it's job with the spring.
IMO , I don't buy the "hotspot" idea unless the coolant is moving too slow or u are using only water.
If you gut the t-stat, u will always be partially recycling hot coolant around the radiator.
If u must do something, put some small holes round the outer lip of the t-stat but, let the disc do it's job with the spring.
IMO , I don't buy the "hotspot" idea unless the coolant is moving too slow or u are using only water.
11-07-05, 07:45 PM
#5
Originally Posted by 89t295k
IMO , I don't buy the "hotspot" idea unless the coolant is moving too slow or u are using only water.
Here comes the science:
But if there's a loss of coolant due to a leak, an air pocket in the cooling system, a cooling problem that causes the engine to overheat, or some other type of engine problem that causes normal combustion temperatures to soar (such as loss of EGR, incorrect ignition timing, a vacuum leak, a lean air/fuel mixture, an exhaust restriction, etc.), the result can be the formation of localized hot spots
source: http://www.federalmogul.com/cda/cont...9_7471,00.html
source: http://www.federalmogul.com/cda/cont...9_7471,00.html
The issue with running without a thermostat is two-fold. The first
part is that the thermostat provides drag on the water flow. This
drag increases the backpressure the water pump and all of the engine
sees. This additional pressure, over and above the nominal 15 psi
static pressure the radiator cap sets, raises the boiling point of
the coolant. The reason this is important is that it suppresses
localized film boiling at hot spots such as around the exhaust
port. The transition from nucleatic boiling (bubbles of steam
originating from irregularities on the surface) to film boiling
(where the hot surface is coated with a film of steam) is called
Departure from Nucleatic Boiling or DNB. DNB is very bad, for steam
is a very good insulator compared to water. Once DNB occurs, the
area under the steam gets hotter because the steam doesn't remove
very much heat, adjacent metal which is still wetted heats from
conduction. DNB happens there. The process spreads until
substantially all the coolant-wetted surfaces are insulated by a
film of steam. The engine overheats. In addition, the buildup in
steam pressure forces the radiator cap open, bleeding coolant,
therefore making the situation worse.
The second issue is that of water pump cavitation and surge. If the
pump is operated at high RPM with insufficient head pressure
(provided by the frictional losses in the coolant passages and the
thermostat), there is a great likelihood that the pump will either
cavitate (localized boiling and/or degassing on the impeller) or
surge (an unstable flow regime). Either phenomena is destructive.
Cavitation's collapsing bubbles act like little sand blaster,
eroding away impeller material. Surge can do the same thing and in
addition, can vibration stress the impeller enough to break it.
Many times what looks like corrosion damage to the impeller,
especially when the housing is damage-free, is actually cavitation
damage.
Source: http://yarchive.net/car/engine_water_restrict.html
part is that the thermostat provides drag on the water flow. This
drag increases the backpressure the water pump and all of the engine
sees. This additional pressure, over and above the nominal 15 psi
static pressure the radiator cap sets, raises the boiling point of
the coolant. The reason this is important is that it suppresses
localized film boiling at hot spots such as around the exhaust
port. The transition from nucleatic boiling (bubbles of steam
originating from irregularities on the surface) to film boiling
(where the hot surface is coated with a film of steam) is called
Departure from Nucleatic Boiling or DNB. DNB is very bad, for steam
is a very good insulator compared to water. Once DNB occurs, the
area under the steam gets hotter because the steam doesn't remove
very much heat, adjacent metal which is still wetted heats from
conduction. DNB happens there. The process spreads until
substantially all the coolant-wetted surfaces are insulated by a
film of steam. The engine overheats. In addition, the buildup in
steam pressure forces the radiator cap open, bleeding coolant,
therefore making the situation worse.
The second issue is that of water pump cavitation and surge. If the
pump is operated at high RPM with insufficient head pressure
(provided by the frictional losses in the coolant passages and the
thermostat), there is a great likelihood that the pump will either
cavitate (localized boiling and/or degassing on the impeller) or
surge (an unstable flow regime). Either phenomena is destructive.
Cavitation's collapsing bubbles act like little sand blaster,
eroding away impeller material. Surge can do the same thing and in
addition, can vibration stress the impeller enough to break it.
Many times what looks like corrosion damage to the impeller,
especially when the housing is damage-free, is actually cavitation
damage.
Source: http://yarchive.net/car/engine_water_restrict.html
11-07-05, 07:58 PM
#6
well after reading that little article and then compairing it with my car that is actaully running no t stat, your car will be ok for quite a while with no thermostat,
ive been running no thermostat at all for the last 40K and the engine is still running strong about to break the 200K mark now.... the car runs very cool highest it gets on the gauge is 1/4 on a hot day, it is an 87 NA and the rest of my cooling system is in order,
ive notice that temp is very low unless i drive the car very agressivly then the temp will cimb up to about 1/4 or if the day is very hot..
however i would recomend using a thermostat as i notive it tends to keep the temperature very stable even when driving very hard. as welll as blocks the bypass which will give you better cooling capability.
so its not a omg hurry get a thermostat its gonna blow up in a day , type of thing, its more like get one when you feel like it....
ive been running no thermostat at all for the last 40K and the engine is still running strong about to break the 200K mark now.... the car runs very cool highest it gets on the gauge is 1/4 on a hot day, it is an 87 NA and the rest of my cooling system is in order,
ive notice that temp is very low unless i drive the car very agressivly then the temp will cimb up to about 1/4 or if the day is very hot..
however i would recomend using a thermostat as i notive it tends to keep the temperature very stable even when driving very hard. as welll as blocks the bypass which will give you better cooling capability.
so its not a omg hurry get a thermostat its gonna blow up in a day , type of thing, its more like get one when you feel like it....
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11-23-05, 01:04 PM
#8
Senior Member
"Here comes the science"
The pyhics have the right idea...u do not want coolant to get stuck by over taxing the waterpump and it is true that for every +1 psi pressure u add one degree to your boiling point but, I think it has been mis- applied.
The removal of the t-stat will put less load on the waterpump for cavitation and since coolant is not flexable it will have the same pressure throughout the system. If the flow moves twice as fast it will pick up half the heat...still comes out the same unless slow the coolant so much that it boils in the engine.
Anyway, u HAVE to control the bypass valve if you want to remove it.....otherwise u are asking for it and you will not be able to see how hot the coolant is getting IN your engine because it is recycling.
The pyhics have the right idea...u do not want coolant to get stuck by over taxing the waterpump and it is true that for every +1 psi pressure u add one degree to your boiling point but, I think it has been mis- applied.
The removal of the t-stat will put less load on the waterpump for cavitation and since coolant is not flexable it will have the same pressure throughout the system. If the flow moves twice as fast it will pick up half the heat...still comes out the same unless slow the coolant so much that it boils in the engine.
Anyway, u HAVE to control the bypass valve if you want to remove it.....otherwise u are asking for it and you will not be able to see how hot the coolant is getting IN your engine because it is recycling.
11-23-05, 01:36 PM
#10
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Originally Posted by Syncro
Where would someone find an OEM thermostat? 
(online)
(online)
11-23-05, 03:09 PM
#11
Opinions are like........
There is a relationship between the oil and water temps in any engine.
If you're purposely keeping the water too cool, the same might be happening to the oil.
Issue #1:
Oil moisture/condensation can be excessive leading to motor oil sludging or breakdown. Fuel dilution, which is common in rich running rotaries, can also be excessive and cause oil thinning and other crud buildups. No thermostat, IMO, requires more frequent oil changes.
1 oil change = cost of an OEM thermostat, use common sense here!
Issue #2:
Thermopellet-- we all know not to drive aggressively until the oil warms up for proper lubrication/oil cooling... throughout the motor.
If running no water thermostat, it could take longer for the oil to warm up. Sounds simple enough to me. Either keep the water thermostat or replace/mod the thermopellet for full oil flow always.
#1 can be proven by UOA.
#2 can be proven with accurate oil:water temp monitoring, using a stopwatch, from full cold start to hot.
I'll stick with common sense and keep my OEM thermostat especially since winters can be cold.
If you're purposely keeping the water too cool, the same might be happening to the oil.
Issue #1:
Oil moisture/condensation can be excessive leading to motor oil sludging or breakdown. Fuel dilution, which is common in rich running rotaries, can also be excessive and cause oil thinning and other crud buildups. No thermostat, IMO, requires more frequent oil changes.
1 oil change = cost of an OEM thermostat, use common sense here!
Issue #2:
Thermopellet-- we all know not to drive aggressively until the oil warms up for proper lubrication/oil cooling... throughout the motor.
If running no water thermostat, it could take longer for the oil to warm up. Sounds simple enough to me. Either keep the water thermostat or replace/mod the thermopellet for full oil flow always.
#1 can be proven by UOA.
#2 can be proven with accurate oil:water temp monitoring, using a stopwatch, from full cold start to hot.
I'll stick with common sense and keep my OEM thermostat especially since winters can be cold.
11-23-05, 03:19 PM
#12
Former Moderator. RIP Icemark.
Many people remove the thermostat thinking that their engine will run cooler or better, that is a myth.
Generally gas mileage will decrease, engine longevity will decrease and the above-mentioned issues will occur.
A rotary engine running at proper temp will give you increased mileage (as the coolant sensor reports the engine is at operating temp- and the ECU takes the fuel and timing out of start-up mode).
So with all the bad things that happen why would anyone even want to drive a mile without a OEM Mazda thermostat???
Well, probably the most common response is that some people think that they have increased cooling with no thermostat. This again is a myth. The size of the radiator and the air and coolant moving through it, is the only that can change the amount of cooling the system is capable of. The thermostat only makes sure the engine is operating at the optimized temperature and that the flow is restricted to avoid the above mentioned cavitations and DMB.
Generally gas mileage will decrease, engine longevity will decrease and the above-mentioned issues will occur.
A rotary engine running at proper temp will give you increased mileage (as the coolant sensor reports the engine is at operating temp- and the ECU takes the fuel and timing out of start-up mode).
So with all the bad things that happen why would anyone even want to drive a mile without a OEM Mazda thermostat???
Well, probably the most common response is that some people think that they have increased cooling with no thermostat. This again is a myth. The size of the radiator and the air and coolant moving through it, is the only that can change the amount of cooling the system is capable of. The thermostat only makes sure the engine is operating at the optimized temperature and that the flow is restricted to avoid the above mentioned cavitations and DMB.
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