Overheating issue

[sjburk]

So my 67 250 6 cylinder keeps heating way up. My gauge doesn't show actual numbers for temp just an h and c opposite each other which is new and also a new temp sensor in the block. Every time I drive or just let it idle, the temp shoots all the way up hot to the right side pretty quickly and then after a moment shoots back down nearly all the way and then never usually gets back above halfway. It also usually will force some water out the overflow hose, no matter how many times I let it do so or add more.The motors been overhauled, It's got a new 3 core radiator as opposed to the original two core, new water pump, new heater core, all new hoses, a brand new 13 psi rad cap, I pressure tested the radiator last week and there were no leaks or pressure loss, and I've replaced the thermostat three times first with 2 195 and lately a 180, but it still heats up that first time and then cools back down like a sticking thermostat. All within the last 6 months I believe except the radiator which is about a year old. I've replaced the thermostat 3 times so I don't think that could be it, it holds pressure, and no leaks are visible so what could be wrong?

[71swb4x4]

Have you checked the gauge or sending unit? Temporarily put a gauge in and see where it is actually maxing out.

[geezer#99]

Never fear it sounds normal.
The thermo stays closed till it gets up to temp, then the thermo opens and it takes a few shakes for the coolant to be cooled in the rad. The cooled coolant flows back thru the motor, the thermo closes to bring the temp back up and then settles partly open to maintain your desired temp be it 180 or 195.
Some thermo's just react slower when first opening.
If you have an overflow hose just set your level a coup the coolant sets it's own level.le inches down. It might puke a little until

[special-K]

It shouldn't climb that high. Your thermostat is probably sticking. Check it out.

[litew8]

He's replace it three times already. Mine (not a 67 or 6 cyl) did that at first but is now reading normal. Maybe the chinese metal needs broken in.

[magicoolbus]

If you fill your Rad to the top. After running it to operating temp (lets assume yours is warming up correctly), the water will expand and go out the overflow pipe to a coolant recovery/expansion tank or to the ground, depending on your set up. After several heat cycles, the fluid amount in the radiator should stabilize and will appear a bit low.

[myyamr7]

Sounds like your thermostat is upside down and not allowing the hot water to let it open properly. Once the heat from the hot side reaches the cold side, it finally opens and all is well after that.
Also, if it's not upside down, did you replace it with the same brand every time? If so, try a different brand.
Simple way to see if it is even a thermostat issue, take it out all together and see if it still happens

[special-K]

Often the last part replaced is the first one to check. You can test a thermostat by putting in heated water using a thermometer to see what temp range it is opening at. Does everything look clean in there? How about the radiator hoses,what shape are they in? Could be collapsing,then heat expanding? Just a thought. Didn't really think that one through.

[sjburk]

The hoses are all brand new and I have felt them when the engine is running hot and the bottom hose going to the pump is really hot and the thermo to rad hose is literally room temp another bad thermostat sign. I haven't ever payed attention but this time I bought a murray temp control ultra form oreilly. So I suppose for now I'll take the it's normal advice and drive it this week and see. I only drive about two miles round trip in it every day so I don't worry about major issues hopefully it'll break in or something

[68 IRON]

Use a laser temp guage to determine how hot the different parts of the cooling system is when the thermostat opens. I thought I had a cooling problem when I saw this happen on my truck....same exact pattern. I'm running a 180 stat now which puts my needle right in the middle of the scale.....a little cool in the winter. Using the hand held laser temp guage I could see the temp rise, thermostat open, and check the cooling efficiency across the radiator. These guages arent expensive and will be handy to use anywhere you want to check temps.

[72freak]

Originally Posted by 68 IRON

Use a laser temp guage to determine how hot the different parts of the cooling system is .

There you go. First place to start.

[cdowns]

dont keep filling radiator to the top// fill it to about 2-3 inches from the top and you will b good to go

if you think there is a temp problem take a knnown good therrmometer and take the temp of the coolant

to me it sounds like a normal engine

[myyamr7]

Originally Posted by sjburk

The hoses are all brand new and I have felt them when the engine is running hot and the bottom hose going to the pump is really hot and the thermo to rad hose is literally room temp another bad thermostat sign.

Seems odd the bottom hose is hot, the pump should be pulling coolant from the radiator on the bottom hose, so in theory, it can only get heated if the hot water is being drawn back in from the top hose

[68 IRON]

Originally Posted by myyamr7

Seems odd the bottom hose is hot, the pump should be pulling coolant from the radiator on the bottom hose, so in theory, it can only get heated if the hot water is being drawn back in from the top hose

That does sound fishy....I missed that. Could the pump impeller be installed backwards? When I checked the temps from the different points (thermostat housing, radiator inlet and outlet) you could see the cooling process all the way across....usually about 30 to 40 degrees depending on stat value. For some reason, without physically checking the flow, it sounds as if there is a reverse flow happening.

You could do the hose supply method I used. This will show the t-stat opening and closing and checking flow of radiator/ pump. Empty your coolant and disconnect your upper radiator hose at the radiator. Feed water at gradual rate into the radiator and let the hose drain to the ground...basically flushing the motor. With the engine running you will see it open and close since it is always getting cold water. You will also be able to check water temp at the guage and directly out of the engine. And if water comes out of the radiator with the hose off....well....you have a pump problem.

[67 cst swb]

Originally Posted by myyamr7

...the pump should be pulling coolant from the radiator on the bottom hose, so in theory, it can only get heated if the hot water is being drawn back in from the top hose

The above statement is incorrect...
The Water Pump... PUMPS water out of the engine into the radiator... That's why its called a water PUMP and not a Water Sucker... (was dying to write that)
Anyway... the top hose being not as hot as the lower hose is normal, as this it cooled fluid (from being cooled in the radiator).
What you need to watch for is if the top hose is hot, extremely swelled and has extreme pressure (so much you can't squeeze it at all) This would mean the thermostat is stuck closed.

How the system works is (in general)
The Thermostat starts out closed, lets just say...engine off, cool, pre-start time in the morning. Now you start the engine still cool, thermostat stays closed. It is at this same time the Water Pump is trying to pump the coolant out of the engine, thus warming the engine and creating pressure in the system due to the Thermostat being closed.
Once the engine temp reaches 180 degrees (or whatever temp thermostat you have in it) the Thermostat opens (that is why the spring is on the engine side of the thermostat) and the cooled fluid (from being in the radiator) enters the engine... this is why... if you have a stuck Thermostat your vehicle overheats due to no fluid (cooled) getting into the engine other than what is already in the engine and is continuing to heat up.
I agree with the post of do not overfill the system, heated water/fluid expands... if the system/radiator is overfull, there is no room in the sealed system for the heated/expanded water to go... hence, it spews out the overflow tube once the system reaches the pressure of the radiator cap rating.

Hope this helps...

[Savidio44]

Does the heater work - provide heat? Also - to solve the thermostat problem - take it out. Should run very cool if everything else is working OK

[Ridgeclimber]

If you have confirmed with a heat gun that it is getting hot, by the sounds of it, I would guess maybe a head gasket or cracked head letting compression gases into the coolant system and accumulating under the thermostat. With an air pocket on the under side of the thermostat you will have to get it extremely hot and probably make steam before the thermostat will open when warming up from a cold start. I had a sb chev in my service truck with a blown head gasket that did the same thing. I didn't have time to fix it properly and needed the truck. So I took the thermostat out and drilled a small 1/16 air bleed hole in the center of the thermostat. Then re installed it. Worked temporarily until I could fix it. Or another option is run Evans waterless coolant. It will not boil or expand. It does not expand when heated, no need for a expansion tank. You can take the rad cap off when at 205 degrees, no problems. I have the original two core rad cooling my LS LQ9 6 liter in my 1968 c10 and has never over heated yet.

[sjburk]

I will get a IR temp sensor but what exactly do I check and what should the readings be? Also, if my pump is going backwards or not functioning, how do I check that? I know you explained but I didn't quite understand, sorry. And what would cause that? The water pump can only go on one way so would reverse pumping mean that it's faulty from the manufacturer just curious.

[litew8]

idk much but I doubt a water pump is capable of going in reverse and can only be installed one way, correctly. If it were going bad you'd hear it and/or see it leaking. With the IR sensor, check at thermostat housing. When it reads the temp at which the thermostat opens, check the hose for heat.

[68 IRON]

Ya, I was thinking maybe a serpentine belt setup where it might turn the pump counter to standard V belt....but cant find anything for the sixes.

Get your readings at t stat housings, radiator inlet, different points across the radiator (checking for cold spots indicating blockage) and back around to the block. Just follow the flow.....it should get cooler the farther away from the t stat.

My procedure-
Drain your radiator into a couple jugs (if fresh and clean, you can reuse). Disconnet hose at radiator inlet (this is where you will see the flow as the t stat opens and closes)
With a hose, run water into radiator until water just starts to run out the radiator where you disconnected the hose (you will have to increase flow when the engine is running)

When the engine warms up to the t stat setting, hot water flow will increase momentarily. The flow will slow a bit as the cold water cycles into the engine.
As it opens and closes, check your temp readings. And remember, the lower hose should not get hot.

[sjburk]

Just to clarify... the water flows in the direction specified in the picture (from bottom of radiator through pump through tstat then back to top of rad) and you suggest I remove the hose at the circled area to see the flow? Sorry I just keep getting lost when you begin talking about flow direction and such And my gauge tops out usually where marked in the other picture (between the last line and the large solid white part) before cooling back down after a moment and then will never go back that high although still somewhat hot occasionally. My heater temp in the cab varied allot when I turned it on, it started out cold until the temp topped out and then got really hot as the gauge went down, then went back and forth between kinda warm and pretty hot regardless of what the gauge did it seemed.

[litew8]

Don't know why you'd want to remove the hose, I sure wouldn't dare.

[Sammy]

I have heard stories that the shaft for the water pump can be broken not allowing the impeller to turn causing over heating conditions without seepage through the weep hole. Eventually causing the bearing to fail. Worth the investigation.

[special-K]

That's "hi" but not "hot". It seems the t-stat is slow to react. Either cheap crap part or you have gunked up cooling system. Does it look muddy? I use 1980 deg religiously. Never had a problem getting heat in winter and I like to be as far from boiling as I can. Carburated vehicles require lower ranges than modern fuel injected vehicles.

[67 cst swb]

You have the arrows running in the incorrect direction. Reverse the direction of the arrows.
The water pump... pumps water out of the engine into the radiator thru the bottom hose.
The water flows out of the radiator thru the top hose back into the engine.