A Nissan Sentra Forum banner

1 - 14 of 14 Posts

·
Registered
Joined
·
66 Posts
Discussion Starter #1
When I first noticed that the gauge read H after only 1 mile of driving, I thought it must have been an electrical fluke. There was no steam, and no noticeable loss of coolant. However, it did it again, so I had both thermostats replaced.

Even after thermostats were replaced, intermittent overheating issue is back. No steam, nothing seems super hot, but upper rad hose was hot and lower rad hose was cool after I pulled over; perhaps the car wasn't cycling coolant at the time, or is it a clogged radiator or perhaps the thermostats are stuck again?

Going over bumps seems to jostle the coolant gauge from H, to normal then back to H.

I'm going to replace the coolant temp sensor just in case it is that as it is fairly easy to replace.
 

·
Registered
Joined
·
348 Posts
I think you have a loose connection or partially broken wire in the temp sensor circuit.
The reason I say that is because the FSM shows for our QR that using a resistor in the connector can "trick" the ECU into thinking the engine is hot and put the fans into high speed.
Saying that, do you notice if your fans are at high speed when this happens ?
 

·
Registered
Joined
·
66 Posts
Discussion Starter #3
Hmm - interesting point, but I'm not sure as I usually shut it off. Next time it does it, I'll pull over with it running to see if fan is going.
 

·
Registered
Joined
·
66 Posts
Discussion Starter #4
Hmm, well it seems that the coolant temp sensor didn't fix it; because while I was bleeding the air out of the cooling system after changing the coolant temp sensor, the gauge read H. But get this; it read H AFTER turning the car off with the gauge reading normal, then turning it on 20 minutes later.

After driving for about half a mile, it abruptly went from H to normal again.

Also, the fans do not kick on when the gauge reads H (but one of the fans kicks on when AC is on).

Sound like an some sort of electrical issue?
 

·
Registered
Joined
·
348 Posts
Does sound like an electrical issue. If the ECM got a high temp reading from the sensor then it would put the fans on high speed.
One fan will always be on when the AC is on so that is normal.

How do the top and bottom radiator hoses feel ? Hot and cold or both hot or both cold ?

Once the engine has warmed up (usually once the fast idle has slowed down) you can check the ECM is reading the temp sensor correctly by turning off the engine, disconnecting the temp sensor plug, putting a 150 Ohm resistor across the plug terminals then starting the engine to check the fans run at high speed.
 

·
Registered
Joined
·
66 Posts
Discussion Starter #6
Just did a 1 mile drive today - Coolant gauge read hot again after about a 1/3 of a mile. Radiator fans were not running, top rad hose was hot, lower rad hose was stone cold.
 

·
Moderator
Joined
·
6,666 Posts
Is the lower rad actually cold? Like not even a hint of warmth at all? It should be warm at the very least. Could be a clogged rad? Question I have is this...could you by any chance get an obd2 reader to see live data? Can you see what your actual ect values are? Chances are, either the gauge is faulty of your rad is clogged.
 

·
Registered
Joined
·
348 Posts
Since the bottom hose is cold and the thermostat is mounted directly at the engine coolant outlet hose (hot side) then it seems like a blocked radiator could be the most sensible thing to check next but your fans should be running at high speed anyway so do the fan speed check with a resistor too.
 

·
Registered
Joined
·
4,998 Posts
Clogged rads are extremely rare, but it does happen. I have seen it once or twice.

You could pull the top hose at the engine and pull the bottom hose at the rad. Pour water in the upper hose fast and see how the flow is out of the bottom of the rad.
 

·
Registered
Joined
·
66 Posts
Discussion Starter #10
Well, I took it to the dealership to get diagnosed; they think it's the passenger side radiator fan motor that burned out due to having a header. Even if the passenger side fan won't turn on, the driver side does, so I'm not sure how that can cause the intermittent issue? Not sure how they tested it as only one fan turns on when the AC is on?
 

·
Registered
Joined
·
348 Posts
I had one fan go bad. Knew something was not right when engine started getting hot when low-speed 4WDing one day.
Found out it was a bad fan by using the resistor in the temp sensor plug. This simulates a hot engine and turns on both fans with high speed if it is a dual speed fan.
The dealer probably just used Consult to force both fans on.
 

·
Registered
Joined
·
66 Posts
Discussion Starter #12
Hmm - can one cooling fan going bad be the cause of the coolant gauge reading Hot after 1/3 of a mile of driving from cold? Also, when I pulled over neither of the fans were blowing when it read H, but the dealership said that 1 fan was running - hmm I'm still not too sure what the exact cause is.

Also, now that the weather is hotter, oddly my car hasn't been overheating.
 

·
Moderator
Joined
·
6,666 Posts
Interesting. So they don't think it's a clogged radiator? The FSM states to put a 150ohm resistor in on the ECT connector. It should run both fans, if it doesn't then you have a problem with the fan.
 

·
Registered
Joined
·
66 Posts
Discussion Starter #14
The dealership wasn't able to reproduce the overheating issue, but they identified that one of the cooling fans wasn't working and think that that is the cause of my intermittent overheating, but that doesn't make sense to me. If one of the fans is still running, then it shouldn't be overheating so quickly, and additionally, when the car says its overheating, none of the fans are running, which make it seem like it's an issue with the gauge and not an actual overheating issue. I'll try to verify myself with a resistor if the fans are working or not.
 
1 - 14 of 14 Posts
Top