Overheating weird problem

[msahr]

Howdy... although I don't feel like this problem is specific to this vehicle, my son bought a 1994 Nissan Sentra, we're having a weird problem.

The engine will get hot quickly, the radiator overflow bottle literally "boils" and steam escapes from it. The upper radiator hose is hot, lower is cold (as in you can hold it as long as you'd like, it may be "slightly" and I mean very very little warm. With the heater on full hot, it's barely lukewarm.

With the radiator cap off, if you start the engine, water will geyser out of the radiator when the engine is started, does this as soon as the engine is cranked.

It has a new, Nissan OEM, water pump. New as in replaced yesterday.

All (ALL) hoses have been replaced. Allegedly, it has a new thermostat.

Any ideas? Thanks!

 

[1972FJ55]

Sounds like a thermostat issue to me.

 

[msahr]

That's kinda where I'm leading. Thanks!

 

[LongDuck]

I'm going to go out on a limb and guess that it's a plugged radiator. Typically, when the overflow bottle is bubbling, and yet the lower rad hose is cool to the touch, it means the radiator tubes are so clogged that the coolant can't flow down from the top (hot side) to the bottom (draw side) for the water pump. With the radiator cap off, that will mean any pumped coolant goes straight out the top (*past the radiator cap, and into the overflow system), because it doesn't have anywhere else to go. I'd also guess the thermostat to be alright, because it's allowing coolant flow outside the pump to the radiator when hot - whereas a bad thermostat which isn't opening would only circulate the coolant within the engine - and the radiator would never get hot (upper hose or radiator body), but don't rule that out if you haven't replaced it yourself with a quality part - cheap insurance would be to replace it now before it gets summertime hot.

I'd also think since you've replaced the other parts, you'd be in good shape re: waterpump/hoses. The lower radiator hose (draw side for pump) typically has a large spring inside to prevent the hose from collapsing - when you start it, have you checked to see if the lower hose is collapsed at all? This would also be evident since the pump can't draw from a clogged radiator, creating vacuum on that side.

Looking at generic pictures online, if it looks like this:

then it has plastic upper and lower tanks, which really can't be resealed effectively for very long. Lucky for you, this radiator seems go for anywhere from $95-150, so it won't cost much for a new replacement.

Also, the PO may have used a 'Radiator Stop Leak' product on it which can cause problems with gumming up the tubes in the radiator - but you probably won't get an admission of guilt on that one.

Let us know what you find,