have an 85' chevy S10, with V-6 2.8L...when i run down the highway for a while, after some time, the temp gauge sometimes starts to creep higher and higher eventually leveling off near the high temp zone, and sometimes it just stays right in the middle...
perhaps intermittent thermostat? is it OK in FLORIDA to run a car w/out the thermostat rather than putting a new one in?
PS there is no heater in the car, it's disconnected.
bob
The thermostat only controls how fast an engine heats up. Once hot, it has no effect. Running without one on some engine setups can cause it to run too hot for whatever ten thousand reasons you are about to hear about and why it 'just can't' run hotter.... ;-)
Real life says it isn't a good thing to do.
The new thermostats they sell fail in the wide open position in case of overheating. I would recommend one of those....
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT'sbob wrote:
With a cooling system in good shape, running without a thermostat will cause engine to run at a lower temp, reducing efficiency (gas milage). Since your truck seems to be tending to overheating, it may have other restrictions to flow that might help raise temp. If, however, the only problem is the thermostat, then leaving it out will, as above, hurt fuel economy. Even in 1985 they were running higher temps than in mid century and before, to help raise fuel efficiency and reduce emissions.
On most cars the thermostat DOES make a difference all the time: it sets the operating temp of the engine and constantly adjusts water flow to maintain that operating temperature (IOW, it doesn't "snap" open immediately, it opens slowly to throttle the water flow). If what you say were true, then the engine temperature would vary with load. In a healthy cooling system, that doesn't happen. The engine just sits right at the thermostat temperature (plus or minus a few degrees) and the water flow rate increases with increasing load (temperature starts upward and the thermostat opens wider), or decreases with decreasing load (temperature starts downward and the thermostat closes slightly.
Running without one on some engine setups can cause it
Lots of engines develop wierd water flow patterns without the restriction of the thermostat. They get "eddies" in the head and block that where water doesn't circulate, and water just rushes by elsewehere, so you get localized overheating. The old saw "the water moves too fast for the radiator to cool it off" is complete bull-stuff, though.
I always thought cooling system flow was more like a slow pulse.
My thermostat begins to open at about 75C, and is fully open at 90C. In my engine (Honda), the thermostat resides at the engine end of the lower rad hose. It sort of stands to reason (to me, anyway) that the water in the radiator is probably well under 90C, so when that starts to travel past the 'stat on its way into the block, the 'stat will begin to close up and restrict water passage. As the water in the block reaches 90C, the thermostat will open up again, admitting cooled water back in, at which point it begins to close again, etc., etc., etc.
Maybe a silly notion, but it makes sense to me.
Why would it cause it to run hotter? Taking the thermostat out allows an unimpeded flow of coolant to the radiator. If anything, it will run cooler on average because the coolant never heats up to normal temperature.
To the OP, a stuck open or missing thermostat is bad in the long run because it will sludge your oil by not allowing the engine to reach temperature where moisture is evaporated from the crankcase. It will also take forever to get hot air out of your heater. Other than that, it's fine as a short term situation.
but if there is a restriction to coolant flowing, how does that explain the "intermittency" of the overheating? i.e. it will run for 1 hr straight right at middle temp, then go high for a little while, then back to middle for a while..etc..if it were a restriction, wouldn't it tend to run consistently high all the time?
bob
there is 50/50 mix antifreeze/water....it doesn't leak..oil? what oil? :-) seriously, the oil looks like any oil in an old beater, IMO..
bob
i don't have a heater, the hoses to it have been removed, and a "bypass hose" just run where the heater hoses were supposed to go....
i get your pt about the sludge, but i just want to get about 2 more months out of the car, and don't want to blow the engine on overtemp, would rather run a "cool" engine if necessary?
bob
bob
It can cause many localized hot spots because the lack of the restriction the thermostat provides allows the water to flow through too fast. The heads then get hot areas that flash the water to steam and then your on your way to a dead engine. By having the restriction the water slows down and cools the areas and keeps the engine alive. The water itself will be cooler because it isn't picking up all the heat it can carry.
With all due respect, I don't believe that this explanation will stand up to close analysis. The more flow past a heated surface the better. If, by removing the thermostat, you decrease or stop the internal circulation, then the overheating can be explained. It depends upon the path the coolant takes through the engine.
The water pump can partially cavitate while the thermostat limits flow, because there is no bypass around the internal water jacket, at least in many designs. Centrifugal pumps are good about being able to continue to rotate even though the flow is stopped totally. A positive displacement pump could 'bust a gut' trying to pump against a closed thermostat or restricted cooling system.
The old story about water needing to flow more slowly in order to have time to transfer the heat is, was, and ever shall be bad science.
The thermostat is normally in the line coming 'from' the engine and once open normally stays open. Most vehicles run hotter than the t-stat opening temp.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
Real life says his explanation is correct on a 'lot' of engines. The coolant turns to steam which makes the temp gauge spike and the cap blow off when you stop.
I have seen this happen a lot over the years. I will also figure all those had troubles to start or the person wouldn't have ripped the t-stat out in the first place....
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
Many years ago thermostats did just open and close. Newer ones today actually modulate the flow. One can notice on temperature gauges today a very steady coolant temp, whereas it used to (25 years ago or more) bounce around a lot.
I suspect it IS a thermostat problem. I had a similar situation on my Neon awhile ago- had thermostat replaced, no recurrence of problem. The point about restrictions was intended to be a general or hypothetical situation that would make removing the theromstat not quite so bad. Personally, I would replace thermostat, and not run without it. 'course, I live in Minnesota :-)
Well, there's at least PART of the problem. That "bypass" hose is just letting un-cooled water from the "hot" side of the engine go right back into the (supposedly) cool side of the cooing system, reducing cooling system capacity.
But not on many newer vehicles (including Mopar 2.7L engines).
Actually, it only "stays open" in those newer systems where its in the return line. In the older systems where its in the line coming "from" the engine, it throttles coolant flow according to temperature.
Only by a few degrees, if everything is working right.
How many years? My 1949 Plymouth's thermostat modulates flow. My '66 Dodge, '69 Dodge, and '73 Plymouth all work exactly the same, modulating the coolant flow at the thermostat to maintain a very nearly constant engine temperature.
The very newest actually don't. They work the way you describe the ones "many years ago" working, and the electric fans modulate the temperature even more accurately than the thermostats used to do. These systems are identifiable by the fact that the thermostat is located in the coolant RETURN line from the radiator, and uses a bypass loop to route engine outlet water past the thermostat's sensing element to open or close it, rather than the main flow thru the thermostat.
One can notice on temperature gauges today
My '49 sits PEGGED at 160 degrees. My '66 sits PEGGED at 180 degrees. My '69 sits PEGGED at 180 degrees (except in heavy traffic in 105-degree weather- like yesterday- with the A/C on. It's a 440 Magnum engine and doesn't really like running slow and loaded, but even then it stays below 200.) My '73 sits PEGGED at 195 degrees. All of these are 100% stock cooling systems, working just the way the factory intended.
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