Hey guys,

I have a 1999 civic ex (auto) and the car reaches operating temperature and everything is fine while driving. However, when I get to a light or when I'm parking the car and there's some backing out and backing in, the temperature starts to rise. If I was to get on the gas and rev the engine while the temperature is rising, the temperature starts to drop.

Can someone please help with explaining what's going on and what needs to be fixed?

Thank you in advance.

 

Is the coolant in the reservoir free of oil (suggesting a failed head gasket)?
Is the Civic losing coolant, as shown by the coolant reservoir or white smoke coming out the exhaust pipe?

Do you ever see the radiator fans coming on? If not, then study the attachment and do the following checks:
In the underhood fuse relay box, use a multimeter's continuity feature to check fuses 41, 42, 56 and 57. If blown, replace.
In the underdash fuse relay box, check fuse 17. If blown, replace.
Find the ECT switch. Disconnect the ECT switch. Jumper the connector for the ECT switch.
Turn the ignition key to the On (or II) position.
Does the radiator fan come on? If not, replace the radiator fan relay.
Repeat the check above with the ECT switch. Does the radiator fan come on?

Report back here all that you find.

Next I would suspect a stuck-shut thermostat.

 

Thanks for the reply @honda.lioness and the instructions you provided. I didn't see any oil in the coolant tank, but I think I may have some more coolant flowing in my tank for some reason than I did previously. I'm slightly over the max now with a cold engine.

I checked with the car running and the good news is the radiator fan comes on.

Is it safe to say it's the thermostat then? If so, then how come the car manages to stay cool during driving with the exception of red lights and parking? Is it the air flow that's keeping the engine cool?

 

sah351, understood about the fan coming on and the reservoir level.

Yes, when the Civic is moving, the air flow over the radiator will help cool the coolant, especially if the thermostat is opening properly, and the radiator is not blocked. Because the overheating is only occurring when idling, and the Civic's being in motion lowers the temperature, I tend to believe that the thermostat is working correctly and also, that the radiator is not blocked. But I am not ruling out a failed shut thermostat or blocked radiator just yet. More questions:

When was the last time the timing belt and water pump were replaced? Water pump impellers can corrode. The vanes on the pump can even fall off. A partly failed water pump will greatly reduce the volume of coolant flowing over the engine. Less coolant = more heating of the coolant = higher temperature of the coolant.

Has any work been done on the coolant system recently, such that air got into the system, and whoever did the work failed to properly purge the system of air?

Are you running the air conditioning when you are driving? Are there signs that the condenser fan (next to the radiator fan) is coming on? The service manual section I attached earlier can help with this.

Right now, here are the candidates on which I would focus for the cause of the overheating: Failed or partly failed water pump impeller; head gasket failure; or air in the system. I would want to keep gathering information as follows:

-- Check the oil on the dipstick. Is it milky in appearance? If so, I would suspect a blown head gasket.

-- With the engine cold, remove about a cup of coolant from the reservoir, until the level is below the max mark. Mark the level in the reservoir. Over the next few days, first thing in the morning, check the level in the reservoir. Report back here. If the level keeps rising, I would be concerned that the head gasket has blown.

-- With the Civic parked and engine cold, remove the radiator cap. Have a flashlight handy. Run the Civic at idle. With the flashlight and eye protection, look through the radiator fill neck and observe the coolant. At some point (within about 10 to 30 minutes at summer temperatures), the thermostat should open. When the thermostat opens at a coolant temperature of about 172 degrees F (the spec for your Civic's thermostat), you should see signs of coolant flowing through the radiator. Do you?

-- Here is another check for a failed shut thermostat or blocked radiator: Feel the upper radiator hose and the lower radiator hose. A properly operating thermostat will open at 172 degrees F. If the thermostat is open, the lower radiator hose should be on the order of 20 degree F cooler than the upper radiator hose. If the lower radiator hose feels (a lot cooler) (more than 20 degrees cooler) than the upper radiator hose, then suspect a stuck shut thermostat or blocked radiator.

-- Put the radiator cap back on. With the engine idling, observe the coolant in the reservoir. Do you see bubbles in the reservoir? If so, this indicates a head gasket failure.

 

@honda.lioness I appreciate your thorough response and follow up. Even with a shut thermostat and air flow when in motion, I doubt that would be enough to keep my car from overheating because coolant wouldn't be flowing at all and I don't think air cooling alone would be enough for the engine.

I'll answer in order of the questions you asked:

When was the last time the timing belt and water pump were replaced? I haven't replaced it since I've had the car which was about 130k miles and it has 189k miles now. I don't know if this was previously by the prior owner.

Has any work been done on the coolant system recently, such that air got into the system, and whoever did the work failed to properly purge the system of air? No such work has recently been performed.

Are you running the air conditioning when you are driving? Are there signs that the condenser fan (next to the radiator fan) is coming on? Yes, I do run the AC as needed and yes, the fan does come on. I've seen the condenser fan come on when with the AC.

Check the oil on the dipstick. Is it milky in appearance? No, the oil looked good actually, like it was recently changed.

With the engine cold, remove about a cup of coolant from the reservoir, until the level is below the max mark. Report back here. I'll keep an eye on this. Hopefully there isn't a head gasket issue based on my other answers.

When the thermostat opens at a coolant temperature of about 172 degrees F (the spec for your Civic's thermostat), you should see signs of coolant flowing through the radiator. Do you? Yes, I did see coolant flowing through the radiator as I got on the throttle.

Feel the upper radiator hose and the lower radiator hose. They pretty much felt the same to me. The lower hose may have been ever slightly cooler but they both felt quite hot. You couldn't hold each for more than 1-2 seconds.

With the engine idling, observe the coolant in the reservoir. Do you see bubbles in the reservoir? This will be hard to check for due to the coloring of the hard plastic tank and I forgot to actually check for this specifically. When I did empty out some coolant from the tank, I did not see any traces of oil in the coolant.

While running the car without the radiator cap on and also being on the throttle, I did have the heater on full blast just in case to get any air that may be in the system. I then ran the car with the AC on as some load and also being on the throttle and after a few minutes the temperature did start to rise again and I've attached a picture. I don't believe it would get any higher as I waited a few minutes to see if it would. When I got on the throttle a bit, the temperature dropped again only to rise again soon.

 

OP. With 50K extra miles since you bought it, I would change the timing belt and water pump, just to know you have known good parts installed.As the water pump is removed, you can check for damaged vanes. Also, after 50K extra miles, if you haven't had the thermostat replaced, I would do that too, to insure a known good part is in the system.

 

-- sah351, thank you for your own detailed response. Diagnosing over the internet is, of course, most likely to yield success when such detail is provided.

-- The timing belt and associated parts change interval for a 1999 Civic is normally 105k miles and seven years. If the Civic is driven at temps under –20 degrees Fahrenheit or above 110 degrees Fahrenheit, the interval is 60k miles.

-- Sometimes there's a sticker under the hood or on the timing belt cover indicating when the belt was last changed. Do you see such a sticker?

-- Inspect the front of the radiator. Is there debris blocking it? As needed, clean off the front of the radiator.

-- Warm up the engine to normal operating temperature. Stop the engine. Feel around the outside of the radiator for any cold spots. These would indicate at least partial blockage of the radiator.

-- I do not rule out a thermostat stuck in an intermediate position or possibly sticking now and then.

-- I do not rule out a water pump that has corroded vanes, reducing functionality.

-- Since the age of the thermostat is unknown, and like 95CoupeRI suggests, I would go ahead and replace it with an OEM thermostat, p/n 19301-PAA-306. For changing the thermostat, see
-- Replacing the thermostat involves a radiator drain. You can inspect and replace the coolant. I would use only aftermarket Honda Spec'd Asian vehicle Blue coolant. I prefer the concentrated version of the Asian Blue (Honda spec'd) coolant, still available online (knock on wood) through Autozone. If you see a lot of debris in the coolant, report back here or proceed directly to a thorough flush. I describe how a thorough flush can be done on a Honda of your vintage, without removing the challenging rear engine drain bolt, and using several gallons of distilled water, at https://honda-tech.com/forums/honda-...ngine-3359247/ .

-- After replacing the thermostat and coolant, is there any improvement?

-- If no improvement, and if you do not know the age of the water pump and timing belt, then again like 95CoupeRI posted, I would want to see the condition of the water pump and go ahead and replace other parts under the timing belt covers. As you may know, this is a relatively labor intensive chore, but it also might be necessary. This forum has much discussion of how to replace the timing belt, water pump, and associated parts.

 

This has all the smell of a head gasket starting to seep compression into the cooling system.
After I replaced my head gasket, the temp gauge on mine is as steady as a rock.
Since these use a steel shim head gasket, I would re-torque the head to see if this helps.
What do you have to lose other than some time.
You will be amazed at how loose those head bolts are.