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fredm
User

Oct 20, 2015, 9:57 AM

Post #1 of 15 (918 views)
  post locked   Coolant temp  

1990 S10 Chevy pickup 180,000 miles, auto trans, 4.3 V-6
Coolant temp problem acting just like a sticking thermostat. When driving, dash temp gage pegs and then cools back down to above normal for this truck - about 220 degrees. After it goes back down to about 220, it stays about there whether sitting at idle or at highway speed.
What I've done: Replaced thermostat twice. Replaced radiator cap. Replaced both temp sensors. Topped off coolant level. Still have same problem.
What I've observed: Upper and lower radiator hoses are not collapsing. Fan seems to be operating normally. No leaks or squealing from water pump. Serpentine belt is not loose or slipping. Radiator is not blocked and has good airflow. Best I can tell, there seems to be no internal blockages in the coolant system.
I replaced the water pump and fan clutch about 5 years ago. I also added an aftermarket transmission cooler about 10 years ago.
The water pump design is so simple that I just can't believe that is has just quit pumping. Any ideas will be appreciated.
Thanks,
Fred

(This post was edited by fredm on Oct 20, 2015, 10:02 AM)


kev2
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Oct 20, 2015, 10:19 AM

Post #2 of 15 (906 views)
  post locked   Re: Coolant temp  

check that heater core is not restricted, fan shroud is still there?

I have given up on aftermarket thermostats, such a simple old world part- have had better luck with OEM.

ck that before we dig deeper


Tom Greenleaf
Ultimate Carjunky / Moderator
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Oct 20, 2015, 10:21 AM

Post #3 of 15 (905 views)
  post locked   Re: Coolant temp  

Two thermostats w same results you can rule that out. Do you trust the gauge? This layout should stay at set temp once warmed up no matter idle or at speed.
Just carefully feel upper hose from a cold start for softness and feel it build both pressure and finally get warm even feel warm air off fan.
If hose never builds pressure, pressure check system.


If in question about real temp put to floor vent heat full blast highest temp - that should be about what engine coolant temp is minus some. If it goes cold then warm again by itself it's boiling or air in system.


? Water pump shaft: If it really could break such that it didn't turn all the time or intermittently it would have a cold radiator while overheating - careful checks for where. I TOTALLY DOUBT THAT!
Is antifreeze mix even close to 50/50? Pure antifreeze can do this an no antifreeze can do this.


Would help to have a thermometer to check real temps to know if it's real info or sending bad info,


T



fredm
User

Oct 20, 2015, 10:29 AM

Post #4 of 15 (903 views)
  post locked   Re: Coolant temp  

Heater blows hot air when turned on. So apparently it's not restricted. Fan shroud still in place as original configuration. I agree that aftermarket thermostats are suspect - that's why I replaced the first replacement with a second. Don't think I would have gotten 2 bad ones back to back. But thanks for your input.
Fred


Tom Greenleaf
Ultimate Carjunky / Moderator
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Oct 20, 2015, 11:15 AM

Post #5 of 15 (890 views)
  post locked   Re: Coolant temp  

IDK - both of us hit at once. You can try a better name thermostat just because like Stant has been good.
Asking for heat at radiator both of us for reasons. Boiling won't throw heat and if gauge says pegged wild hot air will feel cold or cool at heater! Don't ask, trust me it's a clue.
If some don't flow that's an issue now ruled out if you feel heat at all sometimes.
New senders and this spike to max. If you ground one of the wires you can make it read max or unplug will stay cold I think. Made sure it's the one for gauge and not coolant temp sensor which is around there too I think black and yellow wires were OE to that one.
Not convinced you are really overheating yet? My toy is a touchless infrared thermo right at thermostat and for non solids like air outlet temp heat up a small item and test that temp. Radio Shack for a cheap one works fine small as a key fob. They can fool you too so practice on things if you do get one.


Gotta know real temps at the right places. Always need to know engine coolant is properly full - this one not that hard so didn't bring that up before.
Would take time but if hose to recovery tank or radiator cap wasn't correct or failed it would drop coolant level at radiator and would be erratic but first fill would show a leak most likely if so,


T



fredm
User

Oct 20, 2015, 1:07 PM

Post #6 of 15 (882 views)
  post locked   Re: Coolant temp  

This is what I've done in the interim: (I wanted to see if coolant was circulating) Engine was cold. Disconnected top radiator hose at thermostat housing and pushed to side. Cranked engine and let run until gage pegged hot again. During this time, observed that no flow was coming from tstat housing or open hose end. Did observe small bubbles in coolant in tstat housing. Turned engine off and let set for a minute. Cranked back up and coolant started flowing good from tstat housing.
I profess my stupidity in what direction the coolant flows - either into the intake thru the tstat or out of the intake to the upper radiator hose. From the observations, it apparently flows out of the intake to the radiator hose.
In any event, I've concluded this - the water pump is obviously pumping coolant. And apparently this second new tstat is not opening as the engine gets hot. Why it opened after turning the engine off, letting it sit for a minute, and then restarting is beyond me!
For info, the first replacement tstat was the best Stant brand they had - supposed to have had a larger heat sink "motor" than standard. Second replacement was a standard tstat. From the above observations, all I know to try is another tstat, assuming the first 2 replacements were bad products. But that seems awfully odd to me - what do you think about trying a third tstat replacement?
Thanks
Fred


Hammer Time
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Oct 20, 2015, 1:36 PM

Post #7 of 15 (879 views)
  post locked   Re: Coolant temp  

Are you sure you have the thermostat installed correctly?



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



fredm
User

Oct 20, 2015, 2:15 PM

Post #8 of 15 (877 views)
  post locked   Re: Coolant temp  

Yes, it's installed with the "motor" side toward the intake. I have a Haynes manual, and that' the way it shows. Plus, both new tstats were installed just the way the old one came out.
Fred


Hammer Time
Ultimate Carjunky / Moderator
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Oct 20, 2015, 2:59 PM

Post #9 of 15 (872 views)
  post locked   Re: Coolant temp  

Are you sure the temp gauge is correct? Have you verified it with an Infrared thermometer? Is it actually steaming or boiling?

If you are getting no circulation it can only be a problem with the thermostat or the water pump.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
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Oct 20, 2015, 3:49 PM

Post #10 of 15 (866 views)
  post locked   Re: Coolant temp  

Fred: I've asked you to verify that it's really overheating at all. Taking the upper hose off is an odd way to test a thermostat but if you are happy with that fine.


Flow is from engine, heat rises, note thermostat is on top to top radiator hose. As things cool they fall normally and by force so return thru lower radiator hose.


What's with this thermostat? Just get the exact specified OE replacement no tricks.


You need some accurate temp device or readings not relying on the dash gauge. This is really spiking should blow up in your face boiling and you haven't said that.


Does it build pressure on its own from cold? If you don't answer these things and don't understand how it should work get help or shown in person. You could be doing something (can't think of too much) all wrong causing this now,


T



fredm
User

Oct 20, 2015, 5:09 PM

Post #11 of 15 (854 views)
  post locked   Re: Coolant temp  

I disconnected the hose to verify that the pump was actually circulating coolant, not to check the tstat operation. And thanks for the explanation of the coolant flow direction. I haven't checked the temp with an independent device. But when the hose is connected and the gage is pegged, the radiator cap is lifting and letting out steam. So it appears that the engine is actually getting too hot.
I'm going to try a new AC/Delco tstat tomorrow. But I have my doubts about brand name products anymore. 2 years ago I had a mechanic install a new electric fuel pump and was adamant that he use an AC/Delco pump. He said fine, but he normally used parts from NAPA, and I would have to go to the Chevy dealer and pick up the pump if that's what I wanted him to use. That's what I did, but printed right on the side of the AC/Delco box it said "Made in Mexico". So it seems that when we shell out our money for brand name products anymore, all we're really getting is the brand name - the companies have sent all their actual manufacturing overseas!
Will let everyone know if the AC/Delco tstat works any better.
Fred


Tom Greenleaf
Ultimate Carjunky / Moderator
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Oct 20, 2015, 6:14 PM

Post #12 of 15 (847 views)
  post locked   Re: Coolant temp  

Parts and quality can suk. GM totally buys and builds whole cars and parts from Mexico and other countries - TMK they all do. Alone means little to you if part is to the specification.
Companies with a good old brand name sell the name to cheapo too. I say you were right with the GM fuel pump. If that dealer messed with you that's not fair but I see that.


You can pull a very old trick with thermostats with a meat thermometer and pan of water on a stove and watch it open. In that you have these that snap out of it don't think it would prove anything.


OK - AC Delco should be high end for thermostats. I like to see brass and will seek out the Stant owned now Robershaw type which is too confused for this issue.


Alternate thermo. The fob I mentioned is right in front of me now! Was $19.99 + $5 for a little 12V battery so not the world. Less than $10 at Harbor Freight and find a cheaper battery if pinching pennies but double check it at the store before you leave and they are REAL iffy with stuff IMO. BTW - just checked mine with body temp and spot on. Ice in a fridge is....... 5F this instant!
Handy in general but if you point that right at thermostat housing metal when it approaches the stamped/marked rating it should read real close to that and hose warms up in your hands up to a bit too hot to touch.


Radiator must be known full. That means even with this easy one when you fill it you start engine the first time with radiator cap off and watch the level. When t-stat opens it will drop. ALL CAUTION WITH ALL OF THIS PLEASE! Fill with pre-mixed antifreeze and put cap on. Run till warm again and let cool down now before removing radiator cap and by feeling lack of pressure in upper hose a clue it wont flash boil at you - it really can and serious burns!
Repeat that till it's stable. Fill reservoir to the warm level marked on that. If system is tight any remaining air should purge out and draw back only coolant so might drop once or twice still. Now you know it's full. If not no observations are going to really count.
Yes - first shot if looking at temp gauge on vehicle might spike and quickly drop to a normal reading.


BTW - Most with thermostat up top as this engine almost don't need to drain radiator at all! Just clean up the small spill as it's on top.


Heater hoses when running should both feel warm on almost all. Not to complicate but run it and know many engines use heater to run coolant to rear of engines as a bypass alone or in addition to a separate hose which a 4.3 doesn't have TMK.
FYI: Coolant thru radiator on this is side to side to end tanks. ENGINE OFF you can feel by hand hotter up top at fan side and cooler at bottom. A cold spot is/as a way to check if radiator is blocked. Again all caution that the engine is off and be fast.


None of this is worth getting hurt over.


Sorry this is giving you a hard time. Stuff happens that is or isn't your fault and has to all of us no doubt just know to look were faster for the issue.


Manuals at best are not a full training course of every possible reason it doesn't work perfectly the first time - know that,


T



kev2
Veteran
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Oct 21, 2015, 11:28 AM

Post #13 of 15 (830 views)
  post locked   Re: Coolant temp  

X2 from first reply.
I have given up on aftermarket thermostats, such a simple old world part- have had better luck with OEM.
see your local chevy draler.


fredm
User

Oct 21, 2015, 12:55 PM

Post #14 of 15 (827 views)
  post locked   Re: Coolant temp  

Problem resolved! It was the original dash temp gage simply giving erroneous readings. (I can't believe that a 26 year old gage with 180K miles failed - LOL!)
But seriously, many thanks to all of you for your inputs, ideas, and advice.
I considered buying and using the Infared Thermometer, but didn't want to buy that and just use it one time. And if it had shown that the engine was cooler than the dash gage was showing, I would have still had the problem of the bad gage. So instead, I bought a new Bosch manual temp gage and installed that today. That proved the original gage to be the problem and solved the problem at the same. (It seems that the older I get, the lazier I get). But the idea of using the thermometer put me on the right track.
Again, thanks to all for your time and trouble,
Fred


Tom Greenleaf
Ultimate Carjunky / Moderator
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Oct 21, 2015, 1:58 PM

Post #15 of 15 (823 views)
  post locked   Re: Coolant temp  

Great! You isolated it and if this gauge isn't bothering you let it be. OE will be hard to find no question and wonder if just gauge or what for that.


Call this fixed for now and should close out thread. Sorry for some lengthy details that were on my mind NOT really believing it was really overheating - stuff happens.


Up to you for assorted thermos and more tools. Some are just too handy for when things are NOT working out.


Good luck with this fix now. Locked to keep spammers out and YOU may request it reopened by any moderator as you wish,


T







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