I have a 95 s10 4.3L V6 auto with 92k miles.
This all started when one day on my way to work the temp gauge got to 260 then quickly fell. It has not gotten that hot since then.
When I start the truck cold and start driving, the gauge climbs to about 215-230 within 10 minutes of driving. Once the gauge hits what ever is the magic mark for the day it quickly falls (10 seconds or less) to about 170-180. Sometimes it will “cycle” up again to 200 or so then fall back to 170-180. Once it is done moving around it stays low and will not move much as I am driving.
I bought an IR thermometer and measured the temperature at various points in the cooling system. The top of the thermostat housing is about 195 or 200 right after it climbs and drops. If I drive for a while around town then check it, the housing reads hotter, about 220 max.
There does not seem to be enough temperature drop across the radiator, I have measured about 15 degrees difference max between the hoses and on some days only 10 degrees difference.
I have replaced the fan clutch (was bad or going bad), the thermostat, and the radiator cap.
After none of this fixed it, I took it to a mechanic who did a “block test” at my request and said it was fine. He thought what it was doing, climbing and falling was normal.
If I run it without the radiator cap on I do not see much if any flow when I look down into the radiator.
Right now I am thinking of doing the water pump and flushing the radiator this weekend.
I forgot to say this: The gauge seems to be reading wrong. From the measurements I did on the top of the thermostat, the engine is running hotter than the gauge is reading, perhaps there is air keeping the sensor from seeing the coolant temperature?
I have tried to burp the system and it did not help. I have not noticed a loss of coolant, however a good deal of coolant did get pushed into the overflow tank after it got up to 220 after taking it to the mechanic, this fluid did not return to the cooling loop so maybe it was overfilled?
The heat and defrost blows hot as well.
Replacing the water pump may help a little as well as the radiator flush. I think I’m going to agree with your mechanic here and say that the little truck is acting pretty normal. You may have a temperature sending gauge that’s on it’s last legs though. Replacing it first may save you some money.
You have AIR in the cooling system… You also need to check for ANY leaks of coolant…this can and will continually introduce air into the system.
Start by filling both the rad and the reservoir up to the top… Run engine till hot and feel the hoses…the upper and lower should be hot. Allow engine to cool…and you may see the reservoir drop down. Rinse and Repeat untill all air is burped from the system.
If you notice ANY leaks…they need to be fixed or this process will not work. when all air is removed this high and low temp reading will go away.
You can also read up on how to burp the cooling system on this vehicle on the net… this is your basic issue in this instance.
Drill a small (1/16"to 1/8") hole in the thermostat base. These days many thermostats have such a bleed hole but not all and likely yours doesn’t.
Drill a small (1/16"to 1/8") hole in the thermostat base. These days many thermostats have such a bleed hole but not all and likely yours doesn't.
The Thermostat, not the Housing…sorry I figured that better be addressed
My thermostat does have the hole from the factory.
What surprises me is that the gauge climbs then falls, I thought the engine was supposed to reach about 195 then the thermostat would open/close as needed to regulate temperature. The fact I some times see 220 on the thermostat housing tells me the system is not working right.
Blackbird: I did try to burp the system with a “non spill funnel” but perhaps I still did not get all the air out.
You cannot burp the system even if you had a “Magic Funnel” The air in the system I speak of cannot be burped in any other way than either a bleed nipple…or several hot and cold cycles with no leaks in the system. Also make sure your Heater setting is set to HOT…so that coolant goes into the heater core… Remember you cannot have any air or coolant leaks…or the system will never burp itself.
I believe that the temperature sending unit on that engine is located next to the #1 spark plug and the temperature differential from the thermostat to the sending unit can be significant just prior to the thermostat opening. A weep hole in the thermostat base allows hot coolant to flow up to the thermostat even though the thermostat is closed. Many engines these days are designed with bypass thermostats which circulate water to prevent hot spots prior to the thermostat opening. A weep hole will give a similar result.
Whether or not a weep hole is present in this T Stat is Irrelevant. This guy never changed his T stat so the type shouldnt be brought into question. I understand why guys are talking about the weep hole…but this is not coming into play yet. You need to have a full system with no air…for the t stat to function correctly. If a t stat does not have a weep hole as standard…then the mfg of the engine has made arrangements for the t stat to get hot coolant from elsewhere.
""I have tried to burp the system and it did not help. I have not noticed a loss of coolant, however a good deal of coolant did get pushed into the overflow tank after it got up to 220 after taking it to the mechanic, this fluid did not return to the cooling loop so maybe it was overfilled? “”
If the system when hot pushed coolant INTO the overflow container…and did NOT suck any back into the engine upon cooling… we have a problem. It could be as simple as a failing rad cap not sealing which would not allow vacume to build which would suck coolant back up the overflow tube which is in the overflow container. The system MUST be able to Puke up coolant when hot…and pull some in when cold… THIS is the only means of burping the cooling system that this vehicle has at its disposal… Its worked for over 50Yrs so it should still work here.
The temp in the cabin should be on HOT to ensure that the Heater core is included in this Burp process.
Make sure the overflow system is working…make sure it can receive coolant from the hot engine…and ALSO pull coolant back into the engine when cool… This relies on the radiator cap making a good seal… It also relies on NO coolant leaks in hoses or the radiator, also on the tube running from the rad to the overflow…is this tube cracked? crimped anywhere? Can this tube return coolant into the rad? It WILL if the rad pulls a vacume when it cools… It is this exchange of coolant from the rad and into the overflow AND BACK AGAIN is what burps out the air. Any place air can enter the system will foil any attempts to burp it.
Most common causes of not being able to burp? Leaking radiator, leaking hoses…Failed Intake manifold gaskets leaking coolant into the intake ports…or into the lifter valley… Bad Head Gaskets leaking compression into the cooling system. Leaking Heater core… Any time coolant can exit this closed system…AIR will replace it. Think along these lines when trying to repair this situation.
What is the relative position of the thermostat to the upper radiator tank? If the radiator tank is level with or above the thermostat the engine cooling system will purge air/exhaust/vapor whenever the thermostat is open.
The engine could have a failing head gasket and repeatedly overheating one or both heads due to accumulating exhaust will hasten catastrophic failure. A weep hole will greatly slow/reduce the likelihood of catastrophic failure.
Also, a thermostat installed upside down will result in the situation. Could the OP have removed a faulty thermostat and installed a new one incorrectly?
The guy made no mention of the thermostat at all… if he has a bad head gasket…the t stat wont help period
Maybe there’ll be less confusion if I stay out of here for a while. I do so hate confusion.
Well today I replaced the waterpump and temp sender (the one for the gauge). I also back flushed the heater core, flushed the passages I could reach on the engine, and flushed the radiator.
I borrowed a coolant system pressure tester and pumped it up to 15 psi and left it. About 2 hours later it was at 7psi so it does have a leak somewhere. It may well be where the upper radiator hose connects to the radiator, it was hissing but went away when I wiggled the hose (but still leaking somewhere evidently).
Anyway, I installed a prestone easy flush kit on the highest heater hose and filled it with water until it stated coming out the radiator. I then stuck my spill free funnel on the radiator and capped the prestone T fitting. I filled the funnel half way with water and started the engine. I ran it for about 30 minutes and saw some bubbles coming out. There is still some dexcool in the system as the water in the funnel turned dexcool color over time.
I do think the thermostat was working fine because the level of fluid in the funnel would go up and down every few minutes as I guess the thermostat opened and closed.
I watched the temperate on the top of the thermostat housing with the IR thermometer and it never got above 205 or maybe 210… I also watched the temperature on the high and low radiator hose and saw about 170 on the upper and 140 on the lower hose. This is much better then I had seen in the past.
The gauge on the dash never read right during this whole process. It got to 150 and never moved past that point.
Tomorrow I am going to flush some more and then put prestone/distilled water in as I have heard bad things about dexcool.
There are no obstructions between the overflow tank and the top of the radiator, I stuck a garden hose in there and water came out the other side.
Looks like I was the one who was confused… LOL