16 replies to this topic

[eivad1]

im trying to figure out my overheating problem, my 87 hf is getting hot fast and i am feeling the top hose and it is getting hot but the lower hose is cold, bleeding it doesnt help. Could it be the thermostat

[Jaminak]

I'm pretty sure the flow goes the other way. So if the top tube is hot then the thermostat is open. Can you flush you radiator?

[eivad1]

I'm pretty sure the flow goes the other way. So if the top tube is hot then the thermostat is open. Can you flush you radiator?

i could if i wanted to, i am going to take the thermostat back out and try a radiator cap and see if that works, i already tried a new sending unit and obviously that wasnt the problem

[badpenny]

i could if i wanted to, i am going to take the thermostat back out and try a radiator cap and see if that works, i already tried a new sending unit and obviously that wasnt the problem

The system is a gravity feed type. Have you attempted to watch the fluid with the cap off? You may be looking at needing a water pump.

[4N2NR]

Top rad hoses are usually the hot return to the rad. Bottom hoses are usually the cold (or cooler) supply. This is so that if the level is low it will still be able to pump whatever is available to the engine. It should be fairly easy to locate where the overheating is happening:

To verify the water pump take rad cap off and look for good return flow (if good then pump and is not suspect). The return could be good but the thermostat could be opening at the wrong temperature range. If the return is only a trickle suspect stuck closed thermostat or bad pump or even possibly obstructed vanes inside the rad (not allowing suffienct water to the pump).

The only other thing that has any real affect on heat transfer is the radiator itself
Verify the fan(s) rotate and draw sufficient air through the rad fins. Make sure the rad fins aren't obstructed (leaves, too many bugs, too many dings and bends, etc.). Make sure your H2O-coolant mixture is correct.

Sometimes a bad rad cap can cause overheating by not releasing at the proper temp to allow excess to flow to the overflow bottle or it doesn't seat right on the rad.

The only other thing I can think of would be a leak (or block crack) that is allowing post-combustion gases to superheat the water. That usually shows up in other ways such as steam out the tail pipe or milky looking oil. To check for leaks you can do a cooling system pressure check. It is a pump type tool that connects where the radiator cap goes. You pump it up and watch the needle on the pressure gauge to see if any pressure bleeds off (Caution! do not overpressure and cause more problems). If you are loosing pressure it could be the hoses (don't forget to check the ones that go to the heater core too), cracked overflow bottle, pinhole in rad, any gasket near the water channels in the engine, or even the heater core leaking (a blocked heater core usually doesn't cause overheating).

Hope this helps in diagnosing the problem.

[eivad1]

Top rad hoses are usually the hot return to the rad. Bottom hoses are usually the cold (or cooler) supply. This is so that if the level is low it will still be able to pump whatever is available to the engine. It should be fairly easy to locate where the overheating is happening:

To verify the water pump take rad cap off and look for good return flow (if good then pump and is not suspect). The return could be good but the thermostat could be opening at the wrong temperature range. If the return is only a trickle suspect stuck closed thermostat or bad pump or even possibly obstructed vanes inside the rad (not allowing suffienct water to the pump).

The only other thing that has any real affect on heat transfer is the radiator itself
Verify the fan(s) rotate and draw sufficient air through the rad fins. Make sure the rad fins aren't obstructed (leaves, too many bugs, too many dings and bends, etc.). Make sure your H2O-coolant mixture is correct.

Sometimes a bad rad cap can cause overheating by not releasing at the proper temp to allow excess to flow to the overflow bottle or it doesn't seat right on the rad.

The only other thing I can think of would be a leak (or block crack) that is allowing post-combustion gases to superheat the water. That usually shows up in other ways such as steam out the tail pipe or milky looking oil. To check for leaks you can do a cooling system pressure check. It is a pump type tool that connects where the radiator cap goes. You pump it up and watch the needle on the pressure gauge to see if any pressure bleeds off (Caution! do not overpressure and cause more problems). If you are loosing pressure it could be the hoses (don't forget to check the ones that go to the heater core too), cracked overflow bottle, pinhole in rad, any gasket near the water channels in the engine, or even the heater core leaking (a blocked heater core usually doesn't cause overheating).

Hope this helps in diagnosing the problem.

well i knew my thermostat was bad so i took it out fr the mean time, i did put a new rad cap in it but still same problem, top hose hot bottom somewhat luke warm, i tried last week and put a fan that i have to kool my garage down and put it in front of the car, it cooled it down right then n there, then took it away and there went the temp right up. still trying to figure it out

[eivad1]

bump

[tom91ita]

no thermostat is a bad idea. the water pump will not work correctly without some minimal pressure to pump against.

i have had old radiators where the fins are not making good contact on the "core" portion and the car would overheat. but this was a slow progression type of thing.

i found this by trying to flow a little bit of water to flush off some dirt/leaves/bugs, etc. and without jetting the water, the fins just feel out.

sounds like you might have a bad head gasket? have you run low on coolant recently?

how did you know you had a bad thermostat? did you test it in a boiling pan of water to see it open?

[eivad1]

no thermostat is a bad idea. the water pump will not work correctly without some minimal pressure to pump against.

i have had old radiators where the fins are not making good contact on the "core" portion and the car would overheat. but this was a slow progression type of thing.

i found this by trying to flow a little bit of water to flush off some dirt/leaves/bugs, etc. and without jetting the water, the fins just feel out.

sounds like you might have a bad head gasket? have you run low on coolant recently?

how did you know you had a bad thermostat? did you test it in a boiling pan of water to see it open?

the bottom hose was cold no flow, i took out the stat then i got water flow but lukewarm

[eivad1]

whats the weirdest thin gabout this is that it will col down if i get my house fan and put it in front of the radiator. then the guage goes down

[d15a3power]

I'm no mechanic-- but my radiator was redlining whenever I got off the highway--- moving fast, no problem.
I got a flush & new coolant, now she is perfect!

[eivad1]

I'm no mechanic-- but my radiator was redlining whenever I got off the highway--- moving fast, no problem.
I got a flush & new coolant, now she is perfect!

when i sit it gets hot even with the thermostat out, i can just stick my huge house fan in front and it cools down

[d15a3power]

Sounds like the same thing. I went to a Midas type place & now iits fine. I forget how much it was. Good luck!

[eivad1]

Sounds like the same thing. I went to a Midas type place & now iits fine. I forget how much it was. Good luck!

well i rev the car but the water isnt moving, i am going to replace the waterpump and do the belt too, i already put in a new sending unit 180 new thermostat and rad cap, yeah tope house hot bottom hose cold

[Texrex]

Stupid Question: Have you checked your oil? If you have a leak and never noticed you might be low on oil and that will overheat your car no matter how good your cooling system is. Always check the basics just to make sure. Check the pipe that runs under the Intake Manifold for leaks.