overheating issue

[rich67]

ok folks im stumped. a little info first. bought 72 gmc several years ago. had a rebuilt original 307 with like 30 miles on it. has a set of 99 truck heads on it. truck sat for several years with motor covered somewhat but kinda open to the elements. putting truck together. had serpentine system on it that i didnt want so did away with it. put new waterpump on. put in new 190 degree thermostat. put 3 core radiator in that i flushed with water several times before install. so heres whats happening. start truck and let it warm up. temp guage, which is regular guage in the bezel, starts to climb and does not stop. goes all the way to the danger zone before i have to shut truck off as to not harm motor. when truck is warming radiator hoses are cold like no flow. take cap off while running and see no movement of water. if i leave cap tight til truck gets very warm when releasing cap antifreeze/water bursts out the overflow hose when cap gets to first notch. also if you let truck warm up with cap off the water in the radiator doesnt get warm. just doesnt seem to be circulating at all. trying to explain best i can but im at a loss. if any ideas please help. want to get this baby out and drive it but scared to. motor sounds sam good too. its killing me! lol is airlock a possibility? someone mentioned it but i dont know. thanx for your help in advance, rich

[bigmac73]

sounds like the thermostat is sticking closed, i would pull it and run with out it and see if it changes the issues

[bigmac73]

also what kind of water pump did you put back on, i hope you went with a OEM style for the year of motor, i think the serpentine style water pump was a reverse flow , but dont quote me on that, just another idea, I would check thermostat for the first and easiest thing

[rich67]

i know thats exactly what it acts like but i just cant wrap my head around a brand new one being bad. i did try it once without it and it did seem better. just no heat that way right? but it was not the most expensive one the zone had and i have gotten new bad parts there before. i will try again. thanx dude, rich

[rich67]

Originally Posted by bigmac73

also what kind of water pump did you put back on, i hope you went with a OEM style for the year of motor, i think the serpentine style water pump was a reverse flow , but dont quote me on that, just another idea, I would check thermostat for the first and easiest thing

if it is sticking and not letting water go into the motor from the rad then in turn it will not pump it into the rad either? the lower hose doesnt seem to be warming up at all either except for a short part close to the hot motor. i think you are probably right. autozone junk!

[rich67]

Originally Posted by bigmac73

also what kind of water pump did you put back on, i hope you went with a OEM style for the year of motor, i think the serpentine style water pump was a reverse flow , but dont quote me on that, just another idea, I would check thermostat for the first and easiest thing

i went back with the oem style so my belts all work out. i like things simple. lol and i think you mite be rite about the reverse flow of the serpentine waterpump. seems like i read that some where. for a while i wondered if previous owner had put a set of reverse flow heads on it. but i contacted him and he clued me in.

[rich67]

Ok folks time for an update. Problem still exists. Changed rad. Cleaned with acid and water mix and flushed well before install. Pulled water pump to check it out. It seems fine. Put all back together and filled with coolant and same thing. Truck heats up and doesnt stop. Temp just keeps climbing. Cannot see water moving in rad. And water or should say coolant is cold in rad. Can pull thermo and then you can see water move in rad. Truck sat for several years. Could there have formed a partial or full blockage in a water jacket or something? Any thoughts?

[cdowns]

i'd check the water temp by taking a known good hand held themometer and putting it in the radiator

cheapo hand held thmometers are available in the grocery store

[RustyBucket]

With the radiator hoses and the thermostat/outlet off you should be able to stick your garden hose in the water pump and kinda seal it with your hand. Water should flow up out of the thermostat recess after the block fills up. With the water pump off the engine stick the hose in one side and flush it through to the other side. Maybe rats, mice or dirt dobbers plugged up the water jacket. If it doesn't flow I'd figure out how to seal it up and pressure it with the hose.
HAPPY FLUSHING!!

[Lee H]

[QUOTE=rich67;6482947]Truck heats up and doesnt stop. Temp just keeps climbing. Cannot see water moving in rad. QUOTE]

Sounds like a bad water pump to me.

[FirstOwner69]

Did the truck overheat with the serpentine setup on? If it did (or if you don't know), I may have a suggestion for you even though I'm no expert.

[PatrickGMC70]

Your early post isn't clear to me. Did you replace the thermostat? They can definitely be defective and cause overheating.

I got a defective one before. It was in my wife's car. It stuck open and the engine would never heat up. Yours could be stuck closed, which would cause overheating and lack of coolant flow. Start with the easy stuff first.

Also, I don't know from your posts if the engine is actually overheating, or if the gauge is just reading hot. It's possible that the previous owner has the wrong sending unit for your temp gauge.

[rich67]

Originally Posted by PatrickGMC70

Your early post isn't clear to me. Did you replace the thermostat? They can definitely be defective and cause overheating.

I got a defective one before. It was in my wife's car. It stuck open and the engine would never heat up. Yours could be stuck closed, which would cause overheating and lack of coolant flow. Start with the easy stuff first.

Also, I don't know from your posts if the engine is actually overheating, or if the gauge is just reading hot. It's possible that the previous owner has the wrong sending unit for your temp gauge.

i did replace the thermo. was worried i got a bad one but checked it in a pan of hot water and it opened at the rite temp. im not sure what would be the right sending unit. it is in the head. very common type.

[rich67]

Originally Posted by FirstOwner69

Did the truck overheat with the serpentine setup on? If it did (or if you don't know), I may have a suggestion for you even though I'm no expert.

serpentine system never ran. im all ears! lol

[rich67]

[quote=Lee H;6483186]

Originally Posted by rich67

Truck heats up and doesnt stop. Temp just keeps climbing. Cannot see water moving in rad. QUOTE]

Sounds like a bad water pump to me.

it is a brand new one. i took it off again to make sure it spun freely and seemed ok. it spun fine and bearing feels good.

[rich67]

Originally Posted by RustyBucket

With the radiator hoses and the thermostat/outlet off you should be able to stick your garden hose in the water pump and kinda seal it with your hand. Water should flow up out of the thermostat recess after the block fills up. With the water pump off the engine stick the hose in one side and flush it through to the other side. Maybe rats, mice or dirt dobbers plugged up the water jacket. If it doesn't flow I'd figure out how to seal it up and pressure it with the hose.
HAPPY FLUSHING!!

no flushing. my water supply at the shop froze up! damned if u do and...... if you dont! lol it was single digits here most of the day and shop pretty low on insulation. night before though i took the air hose to all the open holes. waterpump ports, thermo hole, heater fittings etc. blew in one side of water pump holes in block and air passed out the thermo hole and when i covered it air came out the other waterpump hole. when it warms up enuff ill get the hose to it. thanx for info dude.

[rich67]

Originally Posted by cdowns

i'd check the water temp by taking a known good hand held themometer and putting it in the radiator

cheapo hand held thmometers are available in the grocery store

no need for a thermometer. lol coolant in rad is plum cool when truck running and thermostat is in place. gonna put it all back together and run it for awhile w/o the thermostat see how it acts after running it for awhile.

[rich67]

thank you all very much for your input. it really helps as i have never had a truck act this way. need to find out for sure about sending unit. if it is correct for guage.

[MARKDTN]

I would get a cheapo mechanical gauge and put it in as well. Then you have a backup to verify the dash one until you figure this out.

How do you know the dash gauge is correct? It may be a mismatch of gauge and sending unit.

[RexDodge]

Originally Posted by rich67

Ok folks time for an update. Problem still exists. Changed rad. Cleaned with acid and water mix and flushed well before install. Pulled water pump to check it out. It seems fine. Put all back together and filled with coolant and same thing. Truck heats up and doesnt stop. Temp just keeps climbing. Cannot see water moving in rad. And water or should say coolant is cold in rad. Can pull thermo and then you can see water move in rad. Truck sat for several years. Could there have formed a partial or full blockage in a water jacket or something? Any thoughts?

Towards the end of this post you mention "can pull thermo and then see water move in rad". So you are saying you removed the thermostat, started the truck and then you could see water circulating when you look into the top of your radiator? If so we may have a winner. When installing your thermostat did you install the button up or down?

[rich67]

Originally Posted by RexDodge

Towards the end of this post you mention "can pull thermo and then see water move in rad". So you are saying you removed the thermostat, started the truck and then you could see water circulating when you look into the top of your radiator? If so we may have a winner. When installing your thermostat did you install the button up or down?

spring down

[rich67]

Originally Posted by MARKDTN

I would get a cheapo mechanical gauge and put it in as well. Then you have a backup to verify the dash one until you figure this out.

How do you know the dash gauge is correct? It may be a mismatch of gauge and sending unit.

i guess i dont really. but water is still cool in radiator. im trying to find out what the correct sending unit looks like.

[rich67]

this is the sending unit that was in head. can anyone tell me if it is the correct one? thanx, rich

[Ironangel]

Looks correct...But NEVER use Teflon tape on those sending units...They need to ground to the block to function properly...There is a conductive pipe dope that can be used that seals and conducts... I'm curious by the way to find out what the issue is with that motor of yours...I'm thinkin, bad water pump or a rats nest in the block somewhere...? Hang in there Pard, you'll figure it out!

[67 cst swb]

Originally Posted by rich67

...rebuilt original 307 with like 30 miles on it. has a set of 99 truck heads on it...

My only input would be:
Do the coolant holes line up properly?
Did they use a head gasket that blocked the holes?
But... I think your use of a garden hose and flushing the motor may have answered that...
just throwing in another thought here...
All the above thoughts I think were on track.