1991 240sx: How do you determine if your radiator is blocked?

[vancouverbc]

Car overheats after driving 20 kms or so. The return hose is always cold. I have replaced the stat and pump lately so I assume I dislodged debris or something that got in rad. Interior heater has no effect on temperature gauge.

[MaximA32]

Remove the lower radiator hose from the radiator and see what kind of flow you get. If you get a restericted flow then you've got a blocked radiator. If it's OEM and you're having trouble with it, I'd suggest replacing it regardless.

[vancouverbc]

Thanks for the help:) The radiator looks after market. My last water pump only lasted a year and was leaking so bad that the coolant gushed out. I was wondering if a blocked rad would be hard on a water pump?

[MaximA32]

It would be extremely hard on a water pump. If the water pump is pumping but where it's pumping to is blocked off, it's going to work too hard trying to pump something that isn't going anywhere.

[vancouverbc]

Thanks. I bled some more and it seem to be ok. Not much air but I guess it doesnt take much. Put car on steep slope and ran with rad cap off.

[DemonZ]

Here's two ways to check the radiator. These ar kinda generic ways to check. first off, run the car till it's alteast normal temp or a little hot. turn off the car, and put your hand on the radiator. I'm not talking about the top, I'm talking about the whole radiator. Feel around if you feel a cold spot... tada, plugged up section in your radiator.

Second method, same as the first... but instead of using your hand, get a water hose.... turn it on a little so that not much water is coming out. then slowly spay a little water on different areas of the radiator. You should see steam, if you dont, then there's your clogged spot.

*edit* though it's not as comon, if you get an air pocket in your block or head, that can cause an overheating problem, and on some cars(though i dont think nissans in general are too bad) it can be a ***** to get that bubble out

[vancouverbc]

Here's two ways to check the radiator. These ar kinda generic ways to check. first off, run the car till it's alteast normal temp or a little hot. turn off the car, and put your hand on the radiator. I'm not talking about the top, I'm talking about the whole radiator. Feel around if you feel a cold spot... tada, plugged up section in your radiator.

Second method, same as the first... but instead of using your hand, get a water hose.... turn it on a little so that not much water is coming out. then slowly spay a little water on different areas of the radiator. You should see steam, if you dont, then there's your clogged spot. Turning on my heater has no effect on the temperture gauge.

*edit* though it's not as comon, if you get an air pocket in your block or head, that can cause an overheating problem, and on some cars(though i dont think nissans in general are too bad) it can be a ***** to get that bubble out

Thanks. My radiator fins are only slightly warm at the very top. The rest of rad fins are cold. However, I have no signs of overheating. I drove for at least an hour in hilly area driving around 60-70 mph. When I came back into town and was in stop and go traffic the temperature was actually slighlty below the normal mark. I guess i will have to test on a warmer day. It was around 7 C which is pretty mild.Turning on my heater has no effect on the temperture gauge.

[DemonZ]

When does it overheat normally? Does it only overheat when you come to a stop or ar in traffic? Or does it overheat even when you are at a 70mph roll?

There are three common things that cause overheating, first is the thermostat, second the pump and third, the fans.

Having a plugged up radiator is still kinda common, but not nearly as common as the first three things I mentioned. Lastly is Air pockets in the motor itself, very rare but it still happens.

If you're overheating mostly in traffic or at a stop, it's probably your fans.

If it was your thermostat, then turning on your heater would help cool the motor down atleast somewhat. Infact... turning that heater on should help atleast a little with any problem you have. So that's kinda strange to me that it has no effect.

Since you replaced the pump and the car does operate at a normal temp now and then, I'll eliminate that as a possible problem.

As I was typing this out I had another idea, since it's not something that happens on most cars and since you said turning on the heater doesnt help I dont think this is it... but since you did mention that the car ran at normal temp today, and it was a mild day, I'll throw this question out there..... Again, this is a rare and since you live up north, probably not likely.... but, do you have A/C? And if you do, has it been retrofitted for R134a? Occasionally on older cars you can get a restriction in the A/C system that can cause a major pressure build up and when you have the A/C on for a while the whole system can heat up so much that the condenser(that's the thing that looks like a radiator that sits in front of your real radiator) gets super heated and since it's pretty much attached to your radiator, it will cause the radiator to heat up quite a bit over normal operating temp causing you car to overheat.... I've only seen this happen on 2 cars, but it is a possibility.