I have a da with a b20b in it. About a week ago I noticed my temp gauge climbing when I woukd get on it. I pulled over and shut the car off to let it cool down. Once I started it back up the temp was fine and it stays cool at an idle. It only beginsbto overheat at high rpms. I replaced the radiator, thermostat and upper and lower radiator hoses the other night. Bled the system and went on a test drive and its still doings the same thing. I also noticed that the lower radiator hose is staying cold while the upper is getting extremely hot. Upper was at almost 200 degrees and lower was at 76. Car runs fine low rpms and stays cool and I can let it idle all day and its fine and I have good heat.I don't know why the lower hose is staying cold and why I'm overheating at high rpms. Any suggestions?

 

Water pump replaced?

 

I'm leaning towards water pump as well
what kind of thermostat did you use? OEM or aftermarket?

 

^
also i would throw that thermostat into a pot of boiling water to make sure it opens.
and another thing, are your fan(s) turning on?

 

Water pump was replaced about 8-9 months ago. Head gasket and all other upper gaskets were replaced as well and the thermostat opened when we boiled it. What about the headgasket or a crack or warp in the head?

 

Thermostat was replaced with a stant OEM. And the fan is wired up to a switch. This is really confusing me.

 

Waterpump was replaced and i also drained and re bled the system and im still having the same issues. Any ideas?

 

Sounds like thermostat is not opening. 94

 

Thermostat is new and was boiled before I put it in. Could it be the headgasket?

 

that makes no difference, it could have gone bad the last time it was installed or sometime after, if the thermostat was opening both upper and lower hoses would be about the same temp. the lower would be a little cooler.

The other possibility is the system still needs bleeding.

As for the HG, are there any other sighs, white smoke from exhaust, milky oil, bubbling in the rad? 94

 

This might sound dumb but make sure you installed the thermostat correctly also try changing your radiator cap. And if there's water or antifreeze leaking check the by pass tube.

 

I changed out the thermostats twice now and both were boiled to ensure that they opened. I have also bled the system 4 different times now. Drained the radiator completely, removed the thermostat, re installed it and filled the radiator back up. Then let it run for about 20 mins with the heat on high and continued to top off the radiator as the level started dropping and the air bubbles were coming out. After bleeding the system completely the lower hose still stayed ice cold and didnt feel like there was much pressure in it. Drove it and was still overheating at high rpms. I have done alot of research online the past couple weeks and have read that the headgaskets will pop in between the cylinder wall and waterjacket? And that this will not show and normal signs of a popped headgasket. The car will still run fine, no smoke and no mixing of fluids. However this will cause the car to overheat at high rpms under high pressure? Does this sound logical to anyone? Would it also explain the lower hose staying cold?

 

Its you headgasket dude ! Thats happens to me long time ago ! 100% headgasket

 

If the HG is blown in to the water jacket you will see "boiling" of the coolant in the rad,

Remove the rad cap, start the engine and rev it keeping an eye on the coolant in the rad, also a blown HG into the water jacket would build pressure beyond what the rad cap can handle and coolant/air would be forced into the overflow bottle.

You can also get a kit from a car parts store to test for HCs in the coolant. 94

 

Keep bleeding the system first it's won't cost you anything But another gallon of coolant nice place to start. When I put my motor back in same problem lower hose stayed cold and upper was hot took me forever to finally all of the air out then the thermostat opened up and it began to cool and let the fans kick on.

 

i would double check all my coolant hoses from the back of the motor, make sure all the hoses are tight and flowing correctly, i had a problem with my b18a overheating and it was because one of my coolant hoses was getting pinched and coolant wouldn't flow. good luck i hope you find your problem.