Engine Running Hot

Tiny
ANDYNAUTA
  • MEMBER
  • 1995 HONDA CIVIC
  • 4 CYL
  • FWD
  • MANUAL
  • 246,000 MILES
I have a 95 civic with 246000 miles on it. It's the EX wit the 1.6 liter SOHC VTEC motor. Around Thanksgiving I changed the head gasket on it because it was leaking. After putting it back together I've been having problems with it running hot. Initially it wanted to overheat all the time and I thought there might be an air bubble in it so I bled it many times and drove it through a few warm up and cool down cycles. The weird part was that when I revved it up the temp would drop but then immediately clime when the engine speed dropped. It still kept wanting to overheat so I tried jamming a bolt in the thermostat to keep it wedged open. It ran cool like this but of course didn't have good heat. Around Christmas time I tried installing a brand new thermostat. This seemed to work a little better but it still didn't run at a consistent temperature. It ran hotter than normal but not too hot. Still the temp would vary with the engine speed as in it would cool down when the engine was revved above about 3000 rpms. A few weeks after the new thermostat I got a check engine light and it would run poorly after leaving cold run mode and before it was completely warmed up. It ran fine when initially started and after being run for at least 15 minutes but in between these stages it would run rough and often stall. The check engine light was for the water temp sensor. There are two sensors in the head near the upper radiator hose one with two wires and one with one wire. I had broken off the one wire sensor when replacing the head gasket and replaced with one from auto-zone that didn't look quite the same so I thought this was the problem. I tired replacing it with one form carquest but it seems to have made no difference. I am now fairly certain that the code is referring to the two wire sensor but don't know if this is related to the engine running hot. Now once it warms up it runs with the temp gauge right at the bottom of the red unless revved at above 3500 rpms. The weird thing is that it never climbs into the red it just stays right there. After a decent drive the radiator feels cold all over even though the temp gauge says the engine was warm. I live in Houghton MI so the outside air temp is cold and I don't know how much the radiator would heat up. The heat works fine but does not feel excessively warm. The upper radiator hose gets hot but not super hot. It seems like either the engine is not getting as hot as the gauge says it is or that there is not enough coolant flowing through. I haven't lost a drop of coolant since the head-gasket change in November. I'm confused as to how the thermostat works being on the bottom side of the engine of this car because it doesn't seem it would get hot there. I would really like to figure this out and am thoroughly confused.
Friday, March 20th, 2009 AT 11:04 AM

35 Replies

Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Hi andynauta,

The ECT is the 2 wire switch which sends signals to the ECM and if it is faulty or has a loose connection, the engine would run rough and even stall after engine is warmed up. Restarting would be difficult as well.

The 1 wire switch is the temperature sending unit and is only for the gauge.

As to the engine running hot, does the radiator cooling fan run continuously or does it stop and run intermittently when temp is showing hot?

Please check out this guide

https://www.2carpros.com/articles/engine-overheating-or-running-hot

Revving up engine to get the temperature down could be due to a bad or weak water pump as the coolant flow is insufficient.

Lack of coolant is another possble cause and since you do not have coolant losses, it should not be the cause.
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Friday, March 20th, 2009 AT 11:25 AM
Tiny
ANDYNAUTA
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  • 4 POSTS
The radiator fan never runs that I have seen. I believe the switch for this is in a sensor in the radiator right? So if the radiator isn't getting warm the fan won't run.

How does a water pump go bad if it's not leaking? I thought there were a centripetal pump so there is no pump seal to go bad. My understanding was that they could either start leaking or freeze up but not pump less well. If they can start pumping less well that would explain the problem but I would like to understand how that would happen.

The coolant is right to the top of the radiator, at the appropriate level in the reservoir and has been bled countless times so that should be good.

Thanks
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Friday, March 20th, 2009 AT 11:34 AM
Tiny
KHLOW2008
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The Fan switch is located on the thermostat housing, not below the radiator.

I have seen many water pumps vanes detached from the shaft. Many others have their vanes worn off, some due to rust and some due to acidity of the coolant used. They would cause insufficient coolant flow.

If the fan is not working, something si wrong. Fan shouls work between 20 to 30 mins upon starting vehicle and work intermittently.

If it is the gauge that is not accurate, it could be due to a bad ground connection at the inner left front fender behind the headlights.
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Friday, March 20th, 2009 AT 2:20 PM
Tiny
ANDYNAUTA
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Is there a way to test the water pump without taking it out?

Also the fan won't turn on if the coolant by the fan switch never gets warm right?
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Friday, March 20th, 2009 AT 2:32 PM
Tiny
KHLOW2008
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Yes, if the coolant does not heat up sufficiently, the fan would not work.

If the water pump is bad, the fan would work non stop as the engine is overheating and the fan switch would be providing a non-stop signal to the relay. By bridging the fan switch connector and with ignition switch ON, the fan should work.

The fan does not work even when the temperature gauge is showing shows a high reading?
Is the reserve tank level constant?

There are no recommended water p[ump testing methods and I normally remove the thermostat and run engine without the radiator cap and watch the coolant flow at the cap neck.
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Friday, March 20th, 2009 AT 3:14 PM
Tiny
ANDYNAUTA
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  • 4 POSTS
I checked the resistance on the coolant temperature sensor and I'm getting 4200 ohms when the engine is cold (40-50) and around 300 ohms when it's hot. These values seem normal from what I've read so I don't know what the problem is there.

After shutting the car off I tried cracking the bleeder after the engine had gotten hot on the drive home today and nothing came out. The system does not seem to be building pressure. Is there any reason it would not build pressure other than the radiator cap? I checked the cap and the spring feels good and the seal looks good but I don't know what else would cause it to not build pressure. The level in the reservoir does go up and down as the engine heats up and cools down.
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Wednesday, March 25th, 2009 AT 5:24 PM
Tiny
KHLOW2008
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If the level in the reserve tank moves up and down by a substantial level, the radiator cap is bad. The pressure valve is faulty.
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Thursday, March 26th, 2009 AT 6:44 AM
Tiny
TWEETERZ
  • MEMBER
  • 1 POST
  • 1995 HONDA CIVIC
Engine Cooling problem
1995 Honda Civic 4 cyl Front Wheel Drive 270000 miles

After driving for about 5minutes I notice the engine temp rise rather rapidly so I checked all my fluids, my coolant was low so I topped that off along with all my other fluids thinking that would solve the problem but still the engine would get hot it extened the problem but it still runs hot I removed the radiator cap and let the engine run and I see no bubbles all my hoses were replaced 6months ago because they cracked, how do I stop the engine from hover heating. Also my gas gauge is off when I start up my car in the morning it shows that it is full but I know its not and after a few minutes it drops and shows the real level of gas but then 5mins later it climbs back up to full. Thank you for your help
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Monday, December 14th, 2020 AT 9:46 AM (Merged)
Tiny
IMPALASS
  • MECHANIC
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Hello -

Thanks for getting back with me.

Sorry for the delay in getting back with you.......I encountered some technical difficulties.......

When was the last time you changed your thermostat?

Do you notice any coolant on the ground under the car at all or any leaks.

Turn the AC and heater off, fan blower off, engine cold.

Start the car and watch the engine radiator cooling fans... They should not be turning... Are they?

Next, with the car still running turn the AC on full... Then look at the engine fans... Are they turning?

Please let me know the above.
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Monday, December 14th, 2020 AT 9:46 AM (Merged)
Tiny
SWB
  • MEMBER
  • 1 POST
  • 1995 HONDA CIVIC
I have a 1995 Honda Civic LX (auto) with 110k miles. About a month ago, it started to idle rough after a warm start. Would be fine (i.E. Stop rough idling) once I started to drive. About 2 weeks ago, my car starting running hot on the way home from work (toward the end of a 45 minutes commute).I noticed it at a stop light, but don't know when it actually started to run hot. The gauge was almost up to the red zone, so I pulled into a parking lot, waited 20 minutes, then drove the rest of the way home (it had cooled down by that time).

Took it in to be repaired. They replaced the battery (which failed all tests) and drained and refilled the coolant (which I admit to not having done in several years). The computer was not telling them anything else was wrong. It ran fine for a few days, then ran hot again at the end of my commute. It did not get to the red zone and as soon as I was able to get moving on the highway, it cooled back down.

Took it back to the shop. They cleaned the fins (is that right?) On the fans and said both were working properly. Also cleaned out some residue in the radiator/tubing (sorry if I have that part wrong. Obviously I'm not an expert) and tested the upper and lower fluid temperature (going into and out of the radiator, I believe he said). Both were the same.

The car ran hot again on the way home from work yesterday. Same situation (although the gauge only reached about 2/3).

The temperature goes back down when I can get moving on a highway, or when I take my foot off the accelerator (if moving in slower traffic). Accelerating in normal traffic (i.E. Around town) is what really seems to cause it to heat up. And only if the car has been running for 30+ minutes. There's no white smoke coming out of the tail pipe, no smells, no dripping when parked, and the car has been well-maintained, with oil changes every 3-4k miles.

Any ideas?
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Monday, December 14th, 2020 AT 9:46 AM (Merged)
Tiny
BRUCE HUNT
  • MECHANIC
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You said they checked the fans and they both checked out ok, but do they check on so to speak when they are requested to? Therefore, are the sensors that tell them to go on working? That would be my question. Your statements about the car cooling down when you go faster indicates that the pump is able to move the fluid around the engine and the radiator gets the cooling going but when it slows the air movement lessens and the car can tend to get warm. That is when the fan should kick in. Have the sensor checked.

When they worked on the coolant level did they replace the thermostat? That could be failing as well. Make sure you keep the resevoir full and check the coolant regularly through this problem so as to avoid overheating the engine and possibly causing the head to warp.

Good luck.
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Monday, December 14th, 2020 AT 9:46 AM (Merged)
Tiny
INTENSEMS
  • MEMBER
  • 1 POST
  • 1995 HONDA CIVIC
  • 4 CYL
  • FWD
  • MANUAL
  • 231,632 MILES
My civic is running hot. I have checked the thermostat. It seems to be fine. I have checked my hoses and they also seem to be fine. Any ideas?
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Monday, December 14th, 2020 AT 9:46 AM (Merged)
Tiny
KHLOW2008
  • MECHANIC
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Hi intenseMS,

When does the overheating occurs?
Did you check the coolant level in the radiator?
Do you have any coolant losses issues?
Are the cooling fans working?
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Monday, December 14th, 2020 AT 9:46 AM (Merged)
Tiny
JOE ZASA
  • MEMBER
  • 3 POSTS
  • 1994 HONDA CIVIC
  • 4 CYL
  • FWD
  • MANUAL
  • 175,000 MILES
Just can't figure this one out! It all started with a leaky water pump, so I replaced the water pump and thermostat. Shortly after that the head gasket went out and so I replaced it. Now with all these new parts engine is still running hot. Although it is very specific when it is running hot. It will only run hot when I am running it at a steady speed for about 10 or 15 minutes, if I stop at a light or shift through the gears it will drop from almost being over the normal range to about halfway on the temp gauge. I have bled the system and I don't think there is any air in the system, and I have also run a flush through the system so I don't think it's clogged anywhere, but I can't be sure. If anyone has any thoughts on how I can make this problem quit I would very much appreciate it, I have put way to much work into this car to not have it run right.
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Monday, December 14th, 2020 AT 9:47 AM (Merged)
Tiny
F4I_GUY
  • MECHANIC
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It sounds like your radiator may be clogged or not flowing properly.

How old is the radiator? Are the fins coming off of it?
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Monday, December 14th, 2020 AT 9:47 AM (Merged)
Tiny
JOE ZASA
  • MEMBER
  • 3 POSTS
Hey thanks for replying,

yeah the radiator is original, that would make sense. I have run a bottle of cleaner through the cooling system but that didn't seem too make any difference at all. When I was changing the thermostat I sprayed water through the radiator and the thermostat housing and it seemed to flow all the way through. Do you know if there is a way I can test the radiator the see if it is clogged? Thank you for your time.
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Monday, December 14th, 2020 AT 9:47 AM (Merged)
Tiny
F4I_GUY
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The only way to test the radiator for clogs is to check for hot spots with a thermal gun. You move the gun across the radiator looking to see if it is being clogged in a certain area.
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Monday, December 14th, 2020 AT 9:47 AM (Merged)
Tiny
JOE ZASA
  • MEMBER
  • 3 POSTS
Hey man I can't thank you enough, I looked up how much the radiators cost for these cars and they are so cheap that I just went ahead and replaced it. It fixed my problem instantly, hasn't heated up at all since I put it in. I am very impressed that you could figure that out from the information I provided you, that was ingenious. Thanks again, Joe
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Monday, December 14th, 2020 AT 9:47 AM (Merged)
Tiny
F4I_GUY
  • MECHANIC
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No problem Joe! This is what I am here for.

Glad you figured it out.
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Monday, December 14th, 2020 AT 9:47 AM (Merged)
Tiny
BTONY86
  • MEMBER
  • 3 POSTS
  • 1994 HONDA CIVIC
Engine Cooling problem
1994 Honda Civic 86,500 miles

1994 Honda Civic LX 86,500 miles and my radiator gauge keeps going up to "H" whenever I'm idle with my foot on the brake (ex: like at a stop sign or drive thru) or when I'm in park. This happens with and without the heat or A/C running. But whenever I accelerate past 30 MPH or so, the gauge goes back down to normal. It never overheats when I'm driving, but only when I'm idle. The check engine light also has a mind of it's own--it comes on periodically but never stays on (sometimes it comes on when I start the car, especially after a rough start, and other times it doesn't). Do you know what's going on and if these problems are connected?
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Monday, December 14th, 2020 AT 9:47 AM (Merged)

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