1995 240sx overheating

[bleufiend]

So I bought this car about a month ago, noticed that it wasnt warming up. Owner before me has just put on a new water pump. I replace a thermostat and it starts to overheat. I run it in the driveway and it seems to not want to overheat idling but will overheat as soon as you take it on a drive. So here is what has been done so far. Took off the head, had it pressure checked, milled to correct some slight warpage and valve seals replaced, installed a new nismo thermostat which I tested before installing and it is opening up at about 160degrees (give or take for my cheap thermometer). I also installed flexalite fans that are made for the 240 and they are set to come on at 175degrees.

All of that and it still overheats. When the car is running and has come up to temp, with the radiator cap off I can squeeze the upper hose closed with my bare hand and the lower hose as well, almost like there is no flow from the water pump. I did take the water pump off while doing the head and theres no play in the impellers. Tryed multiple times to bleed it and it seems that it gets air out of the system but theres just no flow to the radiator. is there a possiblity that the water pump could still be bad even though its new and has no play? Im taking a digital thermometer from a friend today to look for temperature drops across the radiator but other then that Im kind of at a dead end.

[dwaynedman]

Have you checked for a bad cat, or an exhaust restriction. Will definately cause an overheating problem under load condition, but not while parked.Also, is the radiator new ?? Could be a blockage there too..... You will not see much water flow in these radiatos, especially until there is some RPM applied. You did make sure that the thermostat was not backwards right ?? I have actually done that on accident before!! So don't feel bad..Just my .02 !

Later,D

[bleufiend]

The thermostat is installed correctly, spring into block, I have the service manual downloaded and viewed the page with the thermostat before installing it to make sure that I had it in correctly. Also I thought that I may have had a clogged cat as well, I have an exhaust on order, all thats on the car is the stock header and the newly released Started my car up and let it warm up, using the digital thermometer it showed 205 to 210 at the outlet from the block to the radiator but there was absolutely no flow thru the hose out to the radiator. I took the hoses off and also removed the pump, still no play in it, I took a hose and put it on the feed port into the block and ran it, water was coming back out of the front of the block from the port on the left like it should be. I also took the water hoses off to the heater core and the rear one is dispatching water at a agood pace and when putting the hose on the front tube it comes right back out the front of the block. So I dont think I have any blockages in the block, also made sure that the valve on the hose to the heater core was open and I now have it locked to just remain open. The water pump is an aftermarket and the one that advance sold me today is the same brand.

How bad are these airpockets that the KA develops? I mean I had the thing jacked up as far as my hydraulic jack could go and put jackstands under the front to bleed it.

BTW the radiator is still the stock nissan one, car has 125k on it, while I was doing the head I pulled it out and ran the hose thru it, water seemed to come out the other side decently enough.

[dwaynedman]

Sorry for the confusion, I was speaking more of a blockage in the radiator itself. I have never had a problem with bleeding the system on a KA motor. There should be a bleeder screw on your upper hose outlet coming off the engine side. Just take that bleeder all the way out "careful dont loose the copper washer". Just fill your system untill water flows freely out of the hole, and put the bleeder back in.

I have done this numerous times, without major pockets of air. You will never get all of the air out by any bleeding methods, only running the engine and driving it will do that. As long as you have your reservoir filled, air will collect at the top of the radiator, and exchange it with coolant from the bottle.

Keep us posted on the cat, I am curious if that is the problem !!

Later D

[bleufiend]

No I meant to say in my last post that there is no cat on the car right now, its just running a downpipe. I went out this morning and put the water pump back on it and attempted to bleed the cooling system again to no avail. I filled up the radiator and then took the top hose and turned it up so that I could fill the system from the top down. Did that, started it up and ran the motor, started getting warm, upper and lower coolant hoses will get tense, then soft, then tense again then soft. Opened the bleeder screw on top of the upper outlet and it was letting out some fluid, then steam, then just nothing. Using the digital thermometer the temp of the fluid coming out of the radiator outlet is about 215 225, then temp of the fluid going into the motor from the radiator is about 90 to 110.

[dwaynedman]

Open up the bleeder screw while you are filling the system until water runs out. Not while the car is running .... Also you do not need to fill the system from the top hose, just leave the upper radiator hose on while filling. You actually want to fill from the bottom up, as air "rises", it will come out of the bleeder screw. If it keeps overheating that badly, it almost sounds like you have a compression leak into a water jacket. There is no water in your oil right ???? Also we have not stated the obvious, check your radiator cap for cracks on the seating gasket.

Later D

[2black240s]

From experience I know the ka is a PITA whenever you mess with the cooling system. My guess is the problem stems from cooling channels in the head being higher than the top radiator hose. I just had to deal with this last week after a new water pump.

It's going to be messy but you have to burp the heck out of it to get the air out. Run it in the garage with the cap off, have some mixed coolant ready, she will take a liter or two once the thermostat opens. It will take a while, i revv it a few times to speed it up, but it's better than driving it then opening the cap hot. You will want to be squeezing the top hose intermittently through the process. It will start to spit coolant once it gets close to taking more. Just keep letting it spit and adding when you can. Eventually it will take some, just be patient. this takes ~30 or more total, as I said it's a pain. That bleeder screw on the maniolf didn't help me much btw.

HTH

[dwaynedman]

Open up the bleeder screw while you are filling the system until water runs out. Not while the car is running .... Also you do not need to fill the system from the top hose, just leave the upper radiator hose on while filling. You actually want to fill from the bottom up, as air "rises", it will come out of the bleeder screw. If it keeps overheating that badly, it almost sounds like you have a compression leak into a water jacket. There is no water in your oil right ???? Also we have not stated the obvious, check your radiator cap for cracks on the seating gasket.

Later D