I have a 96' civic coupe with a 97' ls engine swap.

My temp gauge never reads more than 1/4 - 1/3 on the dash so I replaced the thermostat with a new OEM thermostat and new gasket.

I filled it back up with coolant at the top of the radiator until it reached the neck of the fill tube, and started the car with the radiator cap off and the heat on full blast (to get the air bubbles out if there was any) and left it run for approximately 20-25 minutes and 5 of those minutes the rpms were held at 2,500.

The car seemed to go in to closed loop but the temp gauge only read 1/3 of the gauge and the radiator fan never came on.

I drove the car for 10 minutes (with the radiator cap on now), parked, and same results

I noticed that the lower radiator hose was cold and the top hose was hot (thermostat is right before the lower hose on the engine side), but I put a brand new thermostat in and followed Honda's procedure for installation and bleeding of the system. And I am positive that the thermostat was installed correctly.

Is there anything else that could cause this problem? Anything that is common in Honda's? I understand that the thermostat could just be bad even though its new but its a pain to get to so I figured I would double check with you guys to see if there is something i should check first, anyone thats done a thermostat on a b18 should understand why I don't want to take it back out haha

Anyways I appreciate any thoughts, And if the thermostat is the only thing it could be than I will go and get another one. Thank you

 

Bump, any thoughts greatly appreciated

 

Does the fan work?

 

You make a good point, stupid me for not testing that

I will post results around 2pm thanks

 

When in doubt about a new good T stat, boil it in water, to see if it opens.

 

Sounds like a stuck open thermostate.

If rad fan does not turn on it may be because engine, [coolant] is not getting to that 190-200 degrees F, or it may be a problem with the rad fan or circuit, circuit and fan can be tested by unplugging the ECT switch, [rad fan switch] and jumping it, if fan runs it's all good, it does not however indicate a good ECT switch, it can be tested with a multimeter, [continuity].

I would also use a temp,"gun" to see what engine temp. actually is after warm up. 94

 

Bad sending unit or gauge?

 

My internet was down yesterday, sorry for not posting back when I said I would

Anyways, I jumped the Engine Coolant Temperature (ECT) switch (the one on the thermostat housing) and my cooling fan turned on so I know that the fan works.
Here is a list of my symptoms that confuse me..
-Car doesn’t reach operating temperature, symptom of a stuck open thermostat.
-My upper hose gets hot
-Lower radiator hose doesn’t get warm/feels like there isn’t coolant in the hose, symptom of a stuck closed thermostat, a clogged radiator, or air in the system BUT my car doesn’t have over heating problems…

Side note: my heat works

How can you test the ECT switch with a multimeter? What should it read? With power on/off? Volts, ohms?

How can you test the Engine Coolant Sending Unit with a multimeter? What should it read? With power on/off? Volts, ohms?

How can you test the Engine Coolant Temperature Sensor with a multimeter? What should it read? With power on/off? Volts, ohms?

Next week I am installing an aluminum radiator and new hoses, at that time I will pull the thermostat out and test it with the temp gun and heat gun method.

Is there a better way to bleed the system than what I explained in my first post?


Conclusion; things I think could be wrong
-bad engine coolant sending unit (how can I test it?)
-bad thermostat
-air in the lines
-clogged radiator

what are your thoughts? Hopefully they're not that I am a complete idiot haha

 

is it tuned? my friend had this problem with his 99 v6 mustang. turns out he went in with his sct tuner and mistakenly changed the tempature at which the fans turn on at (i didnt even think you could do that with a hand tuner). he went back to the fctory tune and that fixed it. idk if you can do the same with your set up but its something to think about.

 

Thanks for the input, The car is running stock ecu the only things done is an exhaust and intake with the ls engine/trans.

 

I think it is the thermostat
stupid question did you put it in backward??

 

ehh not a stupid question haha. I am 99.9% sure that it is in correct, I followed the factory instructions using the Mitchell OnDemand program

 

With the radiator cap off i squeezed the lower hose and the coolant level changes accordingly so there is coolant in the lower hose. I am going to check the coolant temperature tomorrow using a scanner to see if it is a gauge problem and it is just reading wrong. But that doesn't exsplain why the fan isn't coming on.

hopefully someone knows how to test the sensors!

 

if the bottom hose is not changing temp i believe the thermostat is suspect.

try running without it.

fan is turned on by the sensor in the thermostat housing

 

Does the ECT switch measure the temperature before after the thermostat? Because if it is after the thermostat I completly agree. I am just confused about why I don't have an overheating problem if it is stuck closed. So...i was thinking, do you think it could be something stupid like a bad gauge..?

 

The ECT switch, [rad fan switch] is a simple off/on switch it can be tested using the continuity setting on your meter, when engine is cold there will be no continuity between the pins, when engine temp. hits 190-200 degrees F it will close and there will be full continuity between the pins.

If car is running fine the ECT sensor will be good.

The ECT sending unit is a one wire grounding through resistance switch, [yellow/green] switch can be tested with the ohm meter, sorry you will have to look up cold/hot resistance for it, gauge can be checked by grounding the gauge lead, [yellow/green] through appropriate resistance, [resistors] but if it is moving it's a pretty good bet it is OK, however it should still be tested. 94

 

Thanks fcm, I will use the scan tool tomorrow to read the coolant temps and if it gets to 190+ degrees I'll check for continuity at the ECT switch. And I'll go on Mitchell OnDemand tomorrow to check for the resistance chart and test the resistence of the Engine Coolant sending unit and will post results

 

What should the temperature be?Sorry if this is a stupid question.. but also what points should i check the temp? the upper hose?

Also what temperature should the ECT sensor be reading? (what is proper operating temperature?) so I know what to look for when I use the scan tool

 

There are no stupid questions, just stupid answers sometimes.

Proper operating temp. is around 200 degrees F, rad fan should turn on at somplace between 190 and 200 degrees F.

Read temp. at thermostat housing.94

 

My cooling system is 100% but my temp gauge also only goes up to about 1/4. This is how the car has always ran. Car is a 98 Civic with Ls Vtec swap. New hoses, radiator, T stat and the fan work. Just a FIY, pretty normal gauge temp on a Civic.

 

WHAT are you running in your system? Straight water, 50/50... etc????

 

FCM:Thank you

NealnanoHX: I will know when I put the scan tool on it and see what the operating temperature is and also the laser temperature gun

pityocamptes: I am running 50/50

 

if that bottom hose is not changing temp the swich will not see any temp to turn on. got to find out what is preventing it from circulating.

 

50/50 mix. Oh I also live in Arizona where it gets well over a 100 in the summer.
I have had this Civic since it was bone stock with the D16Y5 in it and even then it ran with the same operating temp.

 

If the lower hose is cold and the upper is hot then the T stat is not opening. Make sure you did not put it in backwards, I have seen that done before.