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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Flashback on January 21, 2010, 04:14:37 pm
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86 C10, 305 V8. 89k miles, mostly stock.
Truck started overheating, symptoms were a bad water pump. It would overheat under a load and go back to normal temp stopped at an idle. So I replaced the thermostat, since the truck came with a new one in box. Old one was a 160 unit, new one is OEM 195 degree unit. Still overheats, so I replaced the water pump. Still overheats, same symptoms. Radiator looks fairly new, still shiny. My dad is telling me to get the radiator pressure checked. Coolant is still green. I haven't checked the oil yet for signs of coolant. I just need suggestions at this point, kinda lost. Is it possible for a bad radiator cap to cause this problem? Or am I looking at headgaskets here? The #5 plug seems to be wet when I pull it.
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Did it just start?
I would have the radiator checked. Are you loosing coolant? Does the exhaust smell sweet?
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a bad cap would just cause the antifreeze to boil at a lower temp. the more pressure the higher the temp before boiling. now if you take the cap off while its running dose it boil or just flow? if it looks like its boiling it could be a cracked head or gasket. coolent going bad would cause it to freeze at a higher temp.
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It starts and drives around, but it'll peg the temp gauge out once I start going up hills, etc.
It was losing coolant before but the water pump was leaking. I figured it was toast. Right now I can't find any other leaks. Exhaust smells like old truck. I will investigate more tomorrow after class.
With the cap off I can see it flowing, I don't see any boiling.
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Make sure the lower hose is not collapsing. Check the temp of the radiator. If there's a sudden drop in temp it's clogged.
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How fast are you traveling when going up hill? What is your fan/shroud setup?
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What shape is your fan clutch in? I wouldn't be surprised though if you have a leaking head gasket....
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OK so here is a few more clues to help you guys help me.
Fan clutch is good. It has resistance when I try to spin it by hand when engine is off. From what I've read It disengages above 25-30 MPH. This is when the truck starts to overheat. When I stop and idle for 15 - 30 seconds, it cools back down to 210. So the fan is doing its job. I think Vile is right (of course) and my Dad as well, that there is a clog in the radiator and/or the lower hose is collapsing on me.
Also I checked the oil, no smell or sight of coolant. Coolant is free of oil as well. So HG theory is kaput.
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Just cause there is no coolant in the oil doesn’t mean the heads not cracked. A cracked head can cause gases and all into the coolant leading to the rad. if you do a pressure check on the rad you will see if that's it do one with it running also to see if the gases are slipping pass into the rad
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WTH the new t-stat I put in isn't opening, the upper hose is empty and cold, except near the t-stat, like its barely letting any water thru. Fairly certain I put it in right.
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You can test the T-stat by putting it in a pan of water and see what temperature it opens. If it's opening it sounds like you're getting combustion gases in the cooling system.
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tstats are pretty crappy nowadays, I'd just take it back and get another one, remember pointy side up.
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just remove the t stat and see what it does
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i was having a similar problem with my old pos 305. I bought two t stats and everytime it over heated when i put one in, so i boiled one of the new ones on the stove and it was stuck shut. I went through 3 t stats until i found one that was working properly.
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just remove the t stat and see what it does
That doesn't work because then the water doesn't stay in the radiator long enough to cool off.
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just remove the t stat and see what it does
That doesn't work because then the water doesn't stay in the radiator long enough to cool off.
or it's too cool and wont get a chance to get hot.
It will help diagnose if there is a clogged port or something or bad water pump.
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I'm confused. Without a thermostat it won't stay in the radiator long enough to cool down? I've never heard that. Does removing the thermostat really increase the flow rate that much? Even if it does it just seems counter-intuitive that increased flow would decrease cooling. The radiator is full either way and under the same pressure either way, so I just have a hard time wrapping my brain around that. Can someone explain the theory behind this? If you took an operational vehicle and remove the thermostat it will run hotter?
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read my post again.
I think it becomes more free-flowing therefore it won't really get warm enough to even get your heater working well. Coolant won't stay in the engine long enough to warm up. At least that is my experience and I have run engines w/out t-stadts a few times when needed to prevent overheating.
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iv heard of both a it will cool too much and b it will not cool enough but if you gut it it will slow it down enough to cool it. but anyway forget about that test your old one in the pot and see what it does. how long does it take to warm up? after start up
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Sgt.: sorry I should have quoted him so it wasn't confusing. I was asking about Jim's statement that without the thermostat the coolant wouldn't stay in the radiator long enough to cool off. Nevermind, though. That's a tangent.
just remove the t stat and see what it does
That doesn't work because then the water doesn't stay in the radiator long enough to cool off.
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it will eventually overheat , because it doesn't get a chance to cool is what i should have said. Will take forever to warm up at first though.
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Taking the T-stat out and making it hotter because it's not in the radiator long enough? ???
Heat goes to less heat. It's heat energy that is released at the radiator, the coolant is the means of tansfer. If the radiator is cooler the coolant will be cooler.
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Well guess I'll try switching out the t-stat again. What is the ideal temp unit to get? No A/c, but I do tow cars with this thing. The thermostat I put in was a BNIB Napa 195 degree unit, tho it had been sitting in the glovebox for at least a year.
Oh and it does warm up pretty quick. Seems to be a lot of air trapped in the upper hose. How can I bleed that out?
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195 is good. Idle it cold with the cap off for a min and add coolant I believe to get those air pockets out.
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X2 on the filling up while running, when you pretty quickly you talking about 5 min or what
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Did you check the flow? Did you check the radiator? AS far as bleeding the system everyone here needs to get one of these http://www.tooltopia.com/lisle-24610.aspx?utm_source=googlebase&utm_medium=cse&utm_term=LIS24610&utm_campaign=googlebase_18u
You just put it on the neck of the radiator and allow the engine to reach operating temp. The coolant level will rise and fall as air is released and the t-stat opens. You won't spill coolant everywhere and can be sure the system is full. When it's full shut the truck off squeeze the upper hose and install the plug stop. Release the upper hose and remove the funnel. Saves huge mess from happening.
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Taking the T-stat out and making it hotter because it's not in the radiator long enough? ???
Heat goes to less heat. It's heat energy that is released at the radiator, the coolant is the means of tansfer. If the radiator is cooler the coolant will be cooler.
Ive had to deal with this one before. In cooler areas, the thermostat removal isn't as drastic because there is more temperature drop across the radiator anyway, but it does lead to overcooling. In hotter environments, such as where I live, its not as forgiving. Ive dealt with this primarily on industrial engines, but have also experienced similar problems on a few trucks way back when. Its known that the t-stat holds the coolant in the block long enough to get it hot, and then lets it flow to the radiator. Now, once the slug of cooler coolant hits the tstat it closes and starts the process all over again. (I know alot of you know this, so please don't take offense, some don't) There is normally a 20-40 degree temp drop from the top to the bottom of the radiator depending on the size of the radiator, and ambient temp, etc. Now, with the t-stat removed, the beginning results in overcooling, then can lead to overheating depending on ambient temperatures. When the t-stat stops the coolant in the block to exchange the heat there, it also stops it in the radiator to exchange it there. If the coolant doesn't stop in these two areas long enough, then the block will not be getting the heat removed from it, and the coolant will not be getting as much heat removed from it in the radiator. It has to pause long enough to exchange the heat, even if its just a few seconds.
Ran into this on a hot summer day on an industrial Cat engine. Differential temp from top to bottom of radiator was 5 degrees, no enough exchange because the engine increases more than that, and eventually it would overheat. Good pressure from water pump, clean radiator, good air flow, then found out customer removed t-stats for reasons unknown. Replaced them and engine never saw above 190. Side note, this engine would run about 2 hours before it would overheat after it reached 185 degreesF
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Sorry so long guys, I just hope it helped someone. I forgot to mention, I havent had an issue with the tstat removed on days under 80 degrees F, but the days I did, the temps were over 100 degrees. Ive also got a 4 core radiator in about everything I own, and a smaller one would loose even less heat with out the t-stat there to stop it for at least a brief time.
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i think its more of a prob on newer cars with were the temp sensor helps out with gas and all
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Are you getting heat?