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97 Chevy Astro still overheating


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jsan82
User

Jul 8, 2014, 7:12 AM

Post #1 of 18 (2778 views)
  post locked   97 Chevy Astro still overheating  

Okay so this van is still overheating with the new thermostats. I've tried 2 Stants (SuperStat and regular), 3 Motorads (FailSafe and High Performance), and 1 ACDelco. Every single one does the exact same thing. Temperature gauge slowly rises all the way to redzone. This happens even with air bleed valves on the thermostats or small holes drilled into the thermostat to allow air past. If I put the old open thermostat back in I can drive all day at any speed with no problems other than the engine not reaching normal temperature.

I don't see how I could have installed the thermostats wrong, they only seem to go in one way. I have no idea how I could have gotten 6 failed thermostats. Even gave up and paid $25 for one from the dealer (ACDelco) and I'm still getting the same problem.

Top hose is warm but not hot even at 3/4 mark on the gauge also getting hot air from vents. Coolant level stays stable once the air bleeds out so I'm assuming there are no leaks.

Any ideas? I'm seriously at my wits end with this problem.

Thanks


kev2
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Jul 8, 2014, 8:12 AM

Post #2 of 18 (2761 views)
  post locked   Re: 97 Chevy Astro still overheating  

did you check -
radiator no restrictions both AIR and flow of coolant, could it be partially clogged? feel cold spots OR an IR thermometer.
The heater hoses are still open allowinng flow thru OR bypassing heater core NOT blocking off flow?
Serpentine belt- yes they can be routed incorrectly..
Fans - electric and operating - if belt driven is clutch ok?
Water pump - did you check- maybe missing vanes on impeller OR CCW on a CW system?

The indications of overheating are -
temp gauge? without overflowing purging coolant maybe just a temp sensor problem
If purging could it be a head gasket?

To me it sounds like a radiator issue.. clogged.


jsan82
User

Jul 8, 2014, 12:56 PM

Post #3 of 18 (2743 views)
  post locked   Re: 97 Chevy Astro still overheating  

I'm assuming the water pump is okay. I just replaced it about 4 weeks ago or so and coolant does move through the system when the open thermostat is installed. The top hose only gets barely warm since it has no time for the coolant to heat up and the bottom is cold. So I'm pretty sure that isn't the problem.

The fan clutch is belt driven and I honestly don't have the slightest idea on how to test it. When I had the fan off while replacing the water pump I checked it out. It looks worn but I'm not noticing the fan doing anything that it hasn't done for several years. Will have to do some research on how to even test it before I can make that call.

The serpentine belt is 100% routed correctly. Made very sure of that when I was replacing the water pump.

Is there a way to clear a clogged radiator other than replacing it? Something that I put in there to dissolve it that is stronger than the usual radiator flush chemicals? I tried some from Advance when I changed the coolant about 4 weeks ago. Didn't look like it did anything significant.

I replaced the coolant temp sensor recently also. Van has smooth idle and no smoke from exhaust. Ever had one only cause bad gauge readings other than slamming to C or H?

Going to check the radiators air flow tomorrow. The hoses looked good when I checked them last but I'll do a more thorough check.

Thanks for the info. At least I have a few more things to check.


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jul 8, 2014, 10:31 PM

Post #4 of 18 (2706 views)
  post locked   Re: 97 Chevy Astro still overheating  

? You've done a water pump 4 weeks ago should rule that out. Top hose at thermostat should be the temp of the rating of thermostat when warmed up and flow up out to radiator, cool and return - no big magic in this. If it can't flow that ends that but all at once and so many thermostats doesn't add up at all. That cover if higher temp than thermostat (195F shown) isn't right OR is reading hot if it's cool. IR thermo right there should tell real engine temp or dang close.


4.3 engine - right? I'll keep looking but don't think this block is made with a counter rotating engine but maybe. Fan clutch should blow towards engine and when warm stop quickly and not coast with engine off spinning it. It is (should be) sensing temp of airflow over radiator on how hard it grabs air so if radiator is in fact clogged up that bad it wouldn't be knowing it hot enough to need to work hard.


If top hose isn't getting too warm to touch there's your problem. If it works with a stuck open thermostat and not with a good one something is all messed up. System HAS to be free of air or thermostat could get confused or what coolant is in it doesn't flow enough but then heater wouldn't or shouldn't be blowing hot air either.


Messed up. Test thermostat in water in pan and watch it open if needed. I don't think you can put one in upside down in this as it wouldn't fit in.


Back - Take hoses off radiator if you can't look inside and see it clogged and flush it. If enough junk flush whole system.


?? You just did the water pump and would think any problems with that would have started right then?


T



kev2
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Jul 9, 2014, 2:37 AM

Post #5 of 18 (2699 views)
  post locked   Re: 97 Chevy Astro still overheating  

the time line -

vehicle operated ok-
you changed water pump - WHY? to correct the overheating OR a leaking waterpump and then the problem with overheating?


jsan82
User

Jul 9, 2014, 5:49 AM

Post #6 of 18 (2689 views)
  post locked   Re: 97 Chevy Astro still overheating  

Timeline:

Thermostat failed open so van is not reaching normal operating temp > Replace thermostat and CTS > Now overheating > Hear grinding noise from water pump area > Swap water pump and upper/lower hoses out for good measure (hadn't been changed in several years), the old water pump was actually fine it was the belt tensioner making the grinding noise > Still overheating > Several thermostats later, still overheating.

I've gotten thermostats with jiggle valves to let air past, drilled 2 1/8" holes in another just to see if it would work properly with more areas for air to escape. Still nothing.

I seriously doubt that I got 6 bad thermostats and I've never heard of a CTS only causing bad gauge readings. Always heard a bad CTS would cause poor idle, smoke from exhaust, or a gauge reading that is completely off but I'll test it anyways just to narrow it down.

Won't be able to check anything else until tomorrow morning or so. Going to inspect all the hoses, the radiators airflow and check for any gunk inside, going to get a resistance reading on the CTS terminals, and going to test fan clutch. Also going to attempt to purge more air tomorrow, tried several times today and had no luck. Going to put the front on some jack stands to try and get any bubbles that may be trapped further down.

Just figured it was the thermostat since it seems to work fine with the open thermostat installed. The top hose never gets as hot as you'd expect for 195 degree liquid to be flowing through it. Even right at the thermostat housing it's only warm and I can put my hand on it all day with no pain at all even when gauge is showing it over operating temp. The thermostat definitely isn't in upside down, it's in the way the original was installed. Plus the housing probably wouldn't even seal if it was upside down.

Thanks for the help, hopefully it's something simple.


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jul 9, 2014, 6:27 AM

Post #7 of 18 (2680 views)
  post locked   Re: 97 Chevy Astro still overheating  

Prove me wrong but CTS can be checked and don't think it is for the gauge but rather tells computer how cold the engine is and what amount of fuel to deliver - that's it. Doubt that would make a real overheat or underheat but if really bad would highly likely make it run terrible and codes stored.


Did you ever plain watch a new thermostat open? I can't believe they are all sticking so something else is wrong. You say you have a stuck open one and it runs fine and should be running too cold - not good for it but might behave.


To test fan clutch the spin test by hand or watch it coast just shutting off engine but is temp sensitive so matters how hot it is when checked. You could just spray water thru grill which would cool radiator better than the fan and always run a thermostat's rating doing that fan or not.


Never answered if this is a 4.3 or missed it. If you got the wrong water pump that I wouldn't have replaced if not a problem it might be now somehow but lost about that too.


I'm lost with this. Some how either gauge is wrong or wrong something was done or installed?????


Tom


kev2
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Jul 9, 2014, 7:46 AM

Post #8 of 18 (2679 views)
  post locked   Re: 97 Chevy Astro still overheating  

 toms post had me thinking- there are 2 temp sensors,
for the PCM a 2wire sensor blk/yel at the thermostat.
Another sensor for the gauge a 1 wire DK/Grn in cylinder head @ #1 plug....


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jul 9, 2014, 8:07 AM

Post #9 of 18 (2675 views)
  post locked   Re: 97 Chevy Astro still overheating  

Right kev2 - blk/yellow is just CTS. More troubles with the plug than item but not causing this. Think gauge you can just test out with an OHM meter but no specs on hand or available. IR observations should be enough for real temps for engine sent on to gauge that who knows if working properly now? Tom


GC
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GC profile image

Jul 9, 2014, 8:13 AM

Post #10 of 18 (2671 views)
  post locked   Re: 97 Chevy Astro still overheating  

Have you pressure tested the cooling system? Have you checked for combustion gasses in cooling system? Sure sounds to me like youve got air pockets forming from one source or another.


____________________________________________________
Willing to help, willing to learn... Rob


jsan82
User

Jul 10, 2014, 5:12 AM

Post #11 of 18 (2647 views)
  post locked   Re: 97 Chevy Astro still overheating  

Yes it is a 4.3 sorry forgot that. And yes it has been pressure tested. Yes it runs cold with the open thermostat, that seems to be the only problem.

The water pump came from Advance Auto Part# T3131. They claim it's an exact fit and I had the exact same problem with the old pump on so I don't think the pump is causing it.

I did a hot water test on a couple of the thermostats, 2 were failed closed right out of the box, the other actually opened but not until the water was in rapid boil. Did not have a thermometer at the time to test the actual temperature. Going to get one to test them and see if they are actually functioning correctly.

I was under the assumption that if exhaust gases were getting into the coolant then it would have failed the pressure test and would have bubbles constantly popping up (or coolant discharge from radiator if it's a big leak). It would really suck if the head gaskets blew for some reason, not really looking forward to fixing that.

I tried a little fan clutch test but couldn't do much as a thunderstorm came through. Was only able to try spinning the fan while the engine was cold. It had a lot of resistance, I could spin it but it stop almost immediately after my hand came off of it. Not sure if that tells you anything at all, will do a better test once the weather clears.

I drained the overflow and took a look inside and noticed some gunk, not a lot but enough to cause concern. I'm wondering if the radiator got clogged and can't get enough coolant flow with a proper thermostat but can still function well enough with an open thermostat. Unfortunately I can't find out until the weather clears.

The gauge is original to the van so there's no telling if it's even functioning properly. Would have to research on how to get an ohm or temp reading on it before I can make that call.


(This post was edited by jsan82 on Jul 10, 2014, 5:12 AM)


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jul 10, 2014, 6:57 AM

Post #12 of 18 (2637 views)
  post locked   Re: 97 Chevy Astro still overheating  

Arggh! It runs cold with a known stuck open thermostat and even with problem GC mentioned some will and purge out gasses slow enough that it doesn't show "air" when checked later but problem exists.


Yes - have had a batch, same brands and was being anal about exact temp by a couple degrees and went thru a few and another brand was right on. Just being crazy fussy in that case and wouldn't have been a problem.


I've owned cars with bad head gaskets that "added combustion gasses to cooling system" - story is was picked up late night from a mechanic who promised he just checked antifreeze as it was windy and -10F overnight! I broke radiator and head gasket by sun up. Ticked of course as I would have dealt with it right away as it was fine just the day before and not so cold. Never fixed as it was a cool thing to restore and with that as a start didn't and just limped it till too much of a pest probably drilled out a thermostat so one was there but not sealed tight and did run (quite old car) OK that way but later and sadly junked it.


I'm shocked you found two that failed in boiling water! That or they closed real fast on you?


If you have this problem gasses might not open a good thermostat or near enough and you would come up that it's bad yet again but different brands you said so that's wildly not likely.


To help rule this out and must be slow or you wouldn't find radiator and tank at expected full level cold IMO as you said you did.
You could check for combustion gasses in cooling system - just the vapor in recovery tank but would condemn quite so fast. One or more spark plug may look a lot different than others as in too clean or something clearly different. Hard if this is slow enough and surprising that it would have to bee soooo elusive for this to be the real problem. It could hold pressure testing at a bad gasket but not the pressure of combustion.


Another test is feel upper hose build pressure (know cap is good) and will after a warm up from cold in a few or more minutes just from expansion. If it does that instantly or too fast suspect troubles. Danger is to release pressure while warmed up enough to have pressure and release it taking all care not to get burned from a flash boil. Re-install cap and warm fluid is already expanded so shouldn't build up pressure again real soon and might. A few test that show problems is a condemnation of that happening but still another maybe.


Don't have the pic but a bypass was shown and mentioned already that is pressed into this water pump - right? It's either that or heater core hose - forget sorry if source hose or return but think source. If that isn't flowing properly it could be getting wrong real engine temps and not open a thermostat. Water pumps with thermostat closed are mixing coolant and working still to make all coolant in engine same temp such that thermostat gets the real temp of all coolant in the engine not just one area. Some people will take out a thermostat and the hole of course is so large it flows way too much leaving distant areas hot and may show cool to cold but really overheating in spot away from pump is boiling so never do that. Just stuck open a thermostat continues to circulated inside engine by size of what can pass thru.


Because this pump showed the hose it must be flowing. IDK but follow that hose that it can complete its loop. If to a core for example is must flow thru the core as an acting bypass hose. Folks with bad heater cores are always best to make a loop connection if needed to buy time for a fix not just plug them off.


Troublesome diagnosis on this as both bad luck and probably something slow or this game wouldn't be taking so many tries.


It's going to take more time and testing. Perhaps try pulling plugs, pressure test up no exceeding cap's rating which should be about 15lbs and leave it - cold and a long time. May or not prove diddle but if plugs out later cranking engine one plug hold might spit out coolant OR turn engine by crank bolt and see if it locks as in hydraulic lock. Said may show nothing is those usually burn coolant with no leaks that can do that.


For now keep on testing with a known good thermostat and full. Any and all tests. I think your fan clutch is fine if it stops or you can feel air flow from it with it just at idle should still turn not taxed much to cool harder. Air should feel warm if thermostat is open. Test again is to shut down a warmed up engine for 3-5 minutes. Heat rises so gauge may read high and thermostat will be wide open in about the time it takes to get gas type thing. Wide open, hot radiator a fan clutch could roar for a bit if working properly.


Lots of observations that all is well. Air is possible but must be slight to escape being obvious and you are the lucky one to chase this down and had two known bad thermostats which floors me so far. Sorry for the novel yet again by me but some stuff just doesn't misbehave in "cut and dry" ways,


T



jsan82
User

Jul 10, 2014, 7:23 AM

Post #13 of 18 (2627 views)
  post locked   Re: 97 Chevy Astro still overheating  

The two thermostats that failed closed were Motorad FailSafes (of all things). Did a little research and it seems they are really questionable quality wise. They definitely never opened, I was holding them in the water with a pair of tongs to keep them off the bottom of the pan and watched them the entire time.

Going to tear into this thing as soon as the weather clears. Going to rent the pressure tester again and leave the system pressurized over night and see if there are any noticeable slow leaks. I'll give the spark plugs a check while I'm at it and probably swap them since they are due for changing.

If I can't find the problem I can at least take it to a shop with info on everything that's been checked. May help them narrow it down and save me a couple dollars.

At least I learned to expect the unexpected. Didn't think a simple thermostat swap would cause something like this, not in a million years.

Will do some thorough testing and report back.

Thank you for the help.


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jul 10, 2014, 8:28 AM

Post #14 of 18 (2621 views)
  post locked   Re: 97 Chevy Astro still overheating  

I'll be quick - promise! Pressure tester overnight might lose all pressure especially a rented one but any. Not really made for that long a term IMO.
Actually the one I have can't release it's own pressure so could just let a pressure go sky high and break something. Should be watched when in use now and then.
Good luck, Tom

(This post was edited by Tom Greenleaf on Jul 10, 2014, 8:30 AM)


jsan82
User

Jul 12, 2014, 11:56 AM

Post #15 of 18 (2606 views)
  post locked   Re: 97 Chevy Astro still overheating  

Pressure tested fine. Bought an IR and meat thermometer. Thermostat is fine. The radiator however was only showing 90 degrees (outdoor temp) even when gauge was showing nearly 220 degrees. I could even touch the the front of it (directly behind the grill) with my bare hand after running the engine for 10 minutes and it was cold. That area was right in front of where the top hose connects so I figured it should have been much hotter.

Upper radiator hose, thermostat housing, and heater hoses showed about 175-185. Grill side of radiator 88-90 everywhere I checked. Couldn't get a very reliable measurement on the lower hose since it's so far down and surrounded.

Getting great heat from the vents.


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jul 12, 2014, 3:52 PM

Post #16 of 18 (2598 views)
  post locked   Re: 97 Chevy Astro still overheating  

? Not totally sure what thing was telling you what temp. 220 dash gauge doesn't surprise me if that's what you meant. IR reading can (mine can) be funky and doesn't read air temps for crap - needs an item. Can't speak for all on those,


T



jsan82
User

Aug 7, 2014, 11:25 AM

Post #17 of 18 (2531 views)
  post locked   Re: 97 Chevy Astro still overheating  

Just stopping by to say that it was the temperature sender that was bad. Swapped it out and gauge is now reading where it should and will rise and drop slightly as the thermostat opens and closes.

Gauge is also reading inline with the IR thermometer so all appears to be functioning correctly.

Thanks for the help.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Aug 7, 2014, 12:37 PM

Post #18 of 18 (2527 views)
  post locked   Re: 97 Chevy Astro still overheating  

Thanks for the report of the problem. Will close thread now to keep spammers out,


T







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