Mechanical Problems & Technical Chat If you've got a problem you just can't figure out, a noise you can't diagnose, or a check engine light that won't go away, ask about it here!

1988 Civic LX - Temp sending unit

  #1  
Old 12-05-2013, 03:05 PM
HCF Member
Thread Starter
Join Date: Nov 2013
Posts: 29
Default 1988 Civic LX - Temp sending unit

Since I've had the car, the dash gauge has never gotten to the half way point.

I was told that the previous owner wired a switch to turn on the radiator fans at one time, all of that has since been removed.

When I drive around town for a while, park, I can once in a while smell overheating coolant (if you know what I mean), so I think there is a heating issue, but it's a guess at this point.

Short drives, the gauge reads about 17%
Long drives, the gauge reads about 34% (and that smell I was talking about).

I did find and replace a bad heater hose.
I bled the coolant system.

If I turn on the AC, the radiator fans turn on.

The radiator fan switch (back of engine block) didn't even have one of the wires connected to it. When shorted to ground, the radiator fans turn on.
But I don't know if the switch itself is working (long waits at lights, etc)


Last night, short drive, the gauge never even moved.

At the temp sending unit (below the distributor)...
I shorted the wire to GND, the gauge jumps to HOT (max) instantly.

It's 56F today (engine cold) and
I connected my ohm meter to the sending unit and it read 1800 ohms.
I hit it with a hair dryer for 2 minutes and it read apx 1200 ohms.

1) Can a temp sending unit seem ok when the engine is cold, but still need to be replaced when the engine gets hot?

2) What is the two-wire sensor in front of (next to) the temp sending unit right below the distributor?

Ok, all the electrical itself seems good, and yes it's easy enough to replace the sensors and thermostat, but I don't want to just be replacing parts if it's not necessary.

I have an IR Temp gun but...
3) Where can I get an accurate reading from, and
4) What are "normal" temperature(s)?


I'll pick up a pocket thermometer, and stick it in the radiator cap.

5) If I let the engine idle for (lets say) 15 minutes in the driveway, what should the coolant temp read?

My biggest thing is I just don't know what "normal" is for this car.

Thanks.
 
  #2  
Old 12-05-2013, 03:18 PM
Recognized HCF Member
Join Date: Jun 2007
Posts: 10,023
Default

Don't start new threads about the same problem.

With that said, you really need to pull the thermostat and make sure its not stuck open. If the cooling system is operating normally the engine will stay at the same temperature once its warmed up.

Resistance of the sensor on my car was about 80 ohms at normal temperature (195 F).
 
  #3  
Old 12-05-2013, 11:11 PM
HCF Member
Thread Starter
Join Date: Nov 2013
Posts: 29
Default

Originally Posted by mk378 View Post
Don't start new threads about the same problem.

With that said, you really need to pull the thermostat and make sure its not stuck open. If the cooling system is operating normally the engine will stay at the same temperature once its warmed up.

Resistance of the sensor on my car was about 80 ohms at normal temperature (195 F).

Sorry, the other thread was becoming a novel and I clumped too many things into one thread which I shouldn't have.


Picked up a 180F thermostat and rubber gasket tonight.
They say you don't need gasket sealant when using rubber gaskets, any truth to that?


Is that 80 ohms with the temperature sending unit plugged in or unplugged from the circuit?
 
  #4  
Old 12-06-2013, 06:25 AM
Recognized HCF Member
Join Date: Jun 2007
Posts: 10,023
Default

The gasket wraps around the plate of the thermostat and seals both sides at once-- this will be apparent when you take the old one out. Sealant should not be used. Always use the stock thermostat temperature as the ECU is calibrated to that temperature. Cooler ones are not helping anything.

That resistance was just the sensor. Warm up the engine unplug sensor and measure just the sensor.
 
  #5  
Old 12-06-2013, 08:00 AM
HCF Member
Thread Starter
Join Date: Nov 2013
Posts: 29
Default

Originally Posted by mk378 View Post
Always use the stock thermostat temperature as the ECU is calibrated to that temperature. Cooler ones are not helping anything.

That resistance was just the sensor. Warm up the engine unplug sensor and measure just the sensor.

I didn't choose 180F at random, the auto parts website lists 180F as the OE temp rating:

Murray® Temperature Control Plus 3878 - Standard Thermostat | O'Reilly Auto Parts



You must have asbestos hands to be able to unplug a connector at 195F
 
  #6  
Old 12-06-2013, 12:16 PM
HCF Member
Thread Starter
Join Date: Nov 2013
Posts: 29
Default Bleeder

These are the old and new thermostats, but the bleeder valve on them are going opposite directions. Which one is correct?
 
Attached Thumbnails 1988 Civic LX - Temp sending unit-img_20131206_131025.jpg  
  #7  
Old 12-06-2013, 12:54 PM
Recognized HCF Member
Join Date: Jun 2007
Posts: 10,023
Default

It doesn't matter. You do need to be sure the copper sensing capsule is toward the engine. Rotate so the bleeder pin is at the top, it lets bubbles of air through.

And your picture shows that the old one is stuck open, so you're onto something.
 
  #8  
Old 12-07-2013, 09:54 AM
HCF Member
Thread Starter
Join Date: Nov 2013
Posts: 29
Default

Replaced thermostat and buttoned everything back up.
Still need to road test as it started raining and didn't want to be stuck on the side of the road while it's raining... just in case.


The old gasket is brittle, you can actually snap off pieces of it *sigh*.

When I disconnected the wire from the temp sending unit, it's insulation just crumbled into little pieces in my hand (I'll replace it with a bullet crimp on connector and some heat shrink tubing). Also, the plastic protective sleeve that splits out of the split-loom tubing from the rest of the wiring harness ALSO is brittle and snapped into pieces. very weird.

Upon closer inspection, the YEL/GRN wire going to the temp sender had it's insulation brittle/cracked and seems that a few strands of the (18ga?) wire were broken. I'll have to pull apart the wiring harness to see if there is any good wire left that I can connect a new pigtail to.


With that said...
Is it possible that the coolant temperature sensor going to the ECU (assuming there is one) could be mucked up without me even knowing?

I haven't had the car long enough to know whats good or bad, the engine has been pulled at least once (to replace the tranny) and a previous owner had wired a dashboard switch to turn on the radiator fans. So there's no telling what's right or wrong and that's why I'm not assuming anything here.


I really wish there was a way to read the ACTUAL coolant temp (in degrees), then at least I have something to go off of without just speculating all the time.

I looked at digital temp gauges (even if just temporarily connected) just to get a accurate reading, but they came with their own sending unit, so that really does no good.

Also...
At what temp should the radiator fan switch engage?
I tried looking it up, but couldn't find any temp specs.
 

Last edited by Jymmm; 12-07-2013 at 09:57 AM.
  #9  
Old 12-07-2013, 10:51 PM
HCF Member
Thread Starter
Join Date: Nov 2013
Posts: 29
Default

Originally Posted by Jymmm View Post
At what temp should the radiator fan switch engage?

The "Coolant Temperature Switch" (radiator fan switch) I found
out should turn on above 90C or 194F degrees.

 
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
wkhan69
Mechanical Problems & Technical Chat
3
08-09-2009 10:08 AM
klawrence
Mechanical Problems & Technical Chat
2
11-25-2008 06:03 PM
Dalporto5156
Engine & Internal
0
05-26-2008 06:25 AM
juhasev
Mechanical Problems & Technical Chat
2
07-10-2006 06:21 PM
azcivic
Mechanical Problems & Technical Chat
0
07-18-2005 10:01 PM


Thread Tools
Search this Thread
Quick Reply: 1988 Civic LX - Temp sending unit


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.