Overheating, out of ideas

[mygodrulz]

I have a 1991 Nissan 240 that is having a constant overheating problem. I've replaced the head gasket and checked the head for cracks, checked the radiator flow, replaced the thermostat twice, replaced the water pump, bled the air and set the car so the front is elevated to try and remove all of the air. The only thing that I haven't fixed yet is that the heater performance is only luke warm. According to the coolant flow chart, the coolant exits the rear of the engine, goes through the heater core and exits through a tube that is dumped back into the thermostat area. The car will stay cool for a while during idle and then it will suddenly overheat. The car (except for the heater) had been doing fine until I lost the water pump gasket. I've replaced the water pump, but it's never been the same.HELP!!!!!

[base9se]

Nissan has this device that hooks up to an air compressor and bleeds the air and refills the coolant at the same time. The Nissan Technician that worked on my car on the side showed me this device. It cost around $300 he said. After he drained and refilled my coolant with that device, my car hasn't overheated ever since.

I bled the bubbles at first, but that only slowed the overheating. Meaning it happened just a little less than normal. So, if you want no more overheating you either have to get that device or end up having to go to a Nissan.

If somebody knows the device I'm talking about please post a pic of it, Thanks in advance!

[mygodrulz]

Was it a suction device? If it is, then I have one that I use for brakes called a Vaculla.

[base9se]

Pretty much...it was just hooked up to the radiator. It had 2 plastic tubes and a connection for the air. One tube for the coolant refill, and the other tube was for air to exit out of.

[mygodrulz]

This car has become an extreme dissappointment. Last night we checked the radiator flow capabilities, we tried another thermostat, blew out all of the water hoses, bypassed the heater core and the only thing that finally worked was to remove the thermostat altogether. It appears that the thermostat is not opening because there is no hot coolant circulating around the back of the thermostat to cause it to open. With the thermostat out it has a good flow of water going across and through the radiator. Subaru has the same type of set up where the thermostat is in the lower radiator hose, but I've never had a problem like this one. I tried also to draw coolant out of the air bleed area with a vacuum devise and I even elevated the front of the vehicle to make the filler neck the highest point on the cooling system. The upper radiator hose and the top of the radiator gets extremely hot, but the lower hose and the air being drawn across the radiator witht the fan stays cold. Any ideas? I think that I'm going to rename the car "Firewood."

[Touchdown038]

Did you possibly have the thermostat in backwards?

[mygodrulz]

Tried it, won't go in. Wax pellet and disc goes in toward the block and the pointy part goes toward the radiator. The attachment has the flow chart for the coolant passages and, except for the heater core being stopped off, all lines are clear. We even made a heater core bypass to take it out of the loop.

[metalsyth]

The upper radiator hose and the top of the radiator gets extremely hot, but the lower hose and the air being drawn across the radiator witht the fan stays cold.

I had this problem on my Nissan pickup and it ended up being a small blockage in the radiator. If I were you I would get the radiator check just to rule this out.

[mygodrulz]

Radiator is fairly new. I took and hooked up the garden hose, turned it on full open and it shoved it into the upper inlet. Water passed through without any backing up.

[benemorius]

Just for the sake of eliminating all possibilities, could you describe the procedure used to bleed the coolant system?

[mygodrulz]

We went as far as to raise the front end up on jack stands on an upward sloped drive way to fill it. We removed the plug for the air bleed, filled it up with coolant and started the engine. As soon as coolant was coming out of the air bleed without any bubbles, we installed the plug. I even tried to apply vacuum to the air bleed port with a brake bleeder. The vehicle will get to the point of boiling over and there is no circulation in the radiator. I've checked the radiator for flow, coolant flows fine without the thermostat in it and the lower radiator hose stays cold while the engine overheats. I've tried three thermostats of two different types, installed a new water pump and spent several hours studying the coolant flow. I've blown through all of the coolant passages and hoses and I even made a bypass for the heater core because I know that it isn't flowing very well. I know that cooling systems are not rocket science, but this one is eating my lunch. Here's the coolant flow chart.

[mygodrulz]

Latest development. We drove the car 50 miles yesterday without overheating and no loss of coolant. This leads me to believe that the head doesn't have any cracks in it. I guess that next step will be to try an OEM thermostat.

[mygodrulz]

Needless to say, the 240 has been running for a week now and has not overheated yet with the thermostat out. There isn't any heat, but the engine is staying cool. Is there any expert opinions out there? With the engine running cold, the fuel economy stinks and it's not running with way it's supposed to.

[s13sr20chris]

i would try an oem thermostat. are you mixing the coolant with water?

[s13sucksalot]

mygodrulz is my dad, yeah, we're mixing the coolant with water. Right now it just has straight up water in it though (did want to kill the neghbor's cats by draining anti-freeze everytime we tried something new with the thermostat).

[s13sr20chris]

ok good. gotta check the basics. try to stick with oem parts in situations like this.

[s13sucksalot]

PROBLEM SOLVED!!! After looking at the flow diagram for the coolant and running water through the system at various places, we decided that there was blockage in the hose running from the head to the heater core. Someone probobly put some silver seal or something in it to try and stop a leak. When we put around 20 PSI into said hose, it started gurgling and making all kinds of unblocking noises. just for kicks we shot water through the hose running from the heater core to the throttle body and through the heater core itslef (in hindsight, i'm lucky the thing wasn't cloged, this could have resulted in a REAL mess inside the cabin). Hooked everything back up and warmed up the car. There was a little bit of heat actually coming in. Put in the old thermostat (the one that was originally in the car ) and now i have constant heat and a cool radiator. Thanks everyone for your help!!