[vigsom]

Background

This is a brief report of the issue, diagnosis and solution to the overheat lamp turning on once in a while in a 2013 Honda City, done about 1,43,000km. This is a "Cool Bengaluru" car that belongs to a relative.

Initial Report

The driver of the car reported that

1. the high temperature warning light would turn on at times when the car was in tight traffic/ long traffic signals, and would turn off when the car was in motion
2. the coolant tank level was at full most of the time, with the top external side always wet

Diagnosis

I was attending a wedding in Bengaluru, and was dressed suitably for the occasion. When the driver reported this issue, I was contemplating helping out after the function, but something told me to go for it right then; rolled up my sleeves and asked him to open the hood. I initially suspected a malfunctioning radiator fan motor, asked him to start the engine and the AC, and found the radiator fan speed to be fine.

Observations

1. Radiator cap - found in good condition
2. Radiator level - Radiator top channels were visible and super clean; inference - radiator wasn't fouled, but coolant level in the radiator was lower than normal
3. Coolant Tank - filled to the brim, and color seemed to indicate it was the blue Honda Coolant

I was keen to pull back some of the excess coolant from the tank into a bottle to bring the coolant tank level to its Max mark. When I wanted to do that, discovered that the coolant tank top cap was there, but the coolant tank dip hose was absent; looked into the tank but couldn't find any hose inside.

The radiator inlet cap


Coolant Tank - note the coolant overflow stains


Coolant Tank hose missing

[vigsom]

How the cooling system works

If the dip hose isn't present, the radiator vacuum relief system will not work. Why? Read on

At the cost of sounding repetitive, let me give a brief on how the engine cooling system works. This is without the AC on.

1. When the engine is started up at cold condition, the circulation is just around the block and cylinder head. As the temperature reaches the set point of the thermostat valve ( say, 82 degrees.C), the thermostat opens and coolant circulates through the radiator. The thermostat by now is fully open.
2. Once the engine coolant picks up more heat, the engine coolant temperature (ECT) sensor gives a command to the ECU to start the Radistor fan. The radiator fan runs for just the time required to bring the engine coolant temperature down to the normal ECT value.
3. The radiator has a pressure cap (older cars' caps were set at 0.9 bar, then 1.1 bar, and most recent coolant reservoirs are at 1.4 bar). This cap releases a bit of coolant to the coolant tank to keep the system pressure within the set value
4. Once the engine is shut off, the coolant system temperature drops, and this is accompanied by a gradual reduction in system pressure. As the system goes cold, the vacuum relief valve (seen at the bottom of the radiator cap inside) pulls the relieved excess coolant from the coolant tank back into the radiator. The radiator thus remains full at all times. Whatever loss in coolant is typically seen by a minor drop in level in the coolant tank, which needs to be topped up every now and then.

What happens if the dip hose is absent

Without the coolant tank dip hose, coolant cannot be pulled back into the radiator through the vacuum relief valve. The level in the radiator would deplete when hot and released into the coolant tank, but won't get pulled back when the system gets cold. Thus, the coolant tank level would gradually rise, and then overflow would start. Lesser coolant in the radiator would mean higher temperatures in extreme traffic, thus resulting in the high temperature warning light coming on. When the vehicle is in motion, heat exchange between air and coolant is better and the temperature light goes off. Heat exchangers are typically overdesigned. In a cool city like Bengaluru, the light would likely go off quicker.

What was done to solve the issue

1. Excess coolant in the coolant tank (approx 600ml) was siphoned out, and then transferred back to the radiator. The coolant tank level was thus brought to approx. the MAX mark. Some dilute coolant top up was done in the radiator (approx 300ml or so).
2. New dip hose fixed in the coolant tank
3. System run for a day in stop n go traffic and the coolant tank level was observed steady plus the hi temperature light didn't come on.

What more needs to be done

1. The front bottom left end of the radiator inlet side was observed to have some muddy deposit on it, rendering those fins getting blocked. Although the area is less than 10% of the total surface area, I've requested the driver to have this and the front side of the AC condenser mild - pressure washed
2. Replacement of the coolant with Honda Genuine Coolant at the next service (not sure if it was replaced at around the 1,00,000km mark)

What could have gone wrong

The coolant tank hose might have gotten dislodged and fallen off when the coolant tank cap was opened; oversight by the technician to not fix it back.

Coolant system image with the missing hose indicated (image courtesy boodmo.com)

[Aditya]

Thread moved out from the Assembly Line. Thanks for sharing!

[padmrajravi]

Thank you for such an informative post. I have seen multiple instances of this behaviour in my friends and family members' cars. Engine overheat lamp will come on during traffic jams and will go away on its own when the car picks up speed. In all cases it turned out to be something related to the radiator fan. Once the wires to fan were shorted and another time, the fan itself was stuck. Interestingly , all such instances I have seen were in 8-10 year old cars. Adding one more reason to my checklist to verify the next time I see one.

[nik0502]

This is quite common with old Honda’s I believe. I also found in the past the dip hose missing from the coolant tank. Kept wondering where did it go. Got a new one and fixed it. Couple of years later while doing a full overhaul of cooling system found the dip hose lying at the very bottom of the coolant tank. It was invisible all this while and was only visible once we drained the entire coolant from the tank. On the other hand my mechanic topped up the coolant with regular green coolant instead of blue one. He only added 300-400 ml. Which means the system had 5.5 litters of blue coolant but that little amount changed the colour of entire coolant in the system. For next few days I kept checking by removing the radiator cap if the colour has changed to original blue or a mix of blue and green but no. It stayed green.

[libranof1987]

Originally Posted by vigsom

The front bottom left end of the radiator inlet side was observed to have some muddy deposit on it, rendering those fins getting blocked.

Do have the radiator checked.

We had a similar problem on our '10 City. On a Gurgaon - Mussoorie trip, the a/c stopped cooling so we promptly went to the first a/c service shop that we could find (just outside Noida, around 8am).

He first checked for leaks, confirmed there were none and then topped up the a/c gas.

The a/c worked fine, but a new problem cropped up: the compressor cut off after a few min and then came back on. One diagnosis was the a/c guy probably put in too much gas. So I let some off (post consultation with a mechanic).

The problem persisted, and became a much larger issue: overheating symbol on the dash while ascending towards Dehradun. We somehow limped to Dehradun, and by 4pm managed to find the Honda ASC. They confirmed the radiator was blocked, and hosed it down but that didn't solve it.

They didn't have a radiator in stock, nor did any close by Honda ASCs (we considered leaving the car with them and taking a taxi).

I then checked with them if there were any radiator cleaning shops (years of staying in BTM Layout in Bangalore came in handy - there are tons of shops in the area that I regularly passed). Officially, the SA couldn't tell me, but given my predicament (and as he said, you're with family so I don't want you stranded), he told me to meet him after work hours.

We went to the radiator shop, prioritized our work and sure enough, the radiator fins were awfully blocked. An hour later, and with Honda OEM radiator fluid that the Honda SAs were kind enough to get for me, the a/c functioned good as new.

[ObsessedByFIAT]

Thank you for sharing this write up on one of the most common but disastrous things that can happen to a car engine. The way you explain the problem statement, the troubleshooting steps and the final outcome in all your write-ups is just amazing! You make technical things appear so simple to understand and implement!
Wish to see more such write-ups in future!

My relative's Spark had a similar issue, the only difference was the radiator fins were clogged due to non usage and accumulation of rust due to use of water instead of coolant. It would also heat up in stop go traffic, but would run like a charm on open highway.

My only worry in the above scenario is the missing pipe. It has to be found out and removed from the system, if at all it is still there. That can surely cause a clog in free flow of coolant.

[Shreyans_Jain]

Some problems have the simplest of solutions. A very well diagnosed case with point to point approach. It’s a good thing that these Hondas are inherently very reliable, mechanically. Things like thermostats and valves and radiator caps usually don’t give any trouble. So, it is a leak somewhere, or a missing component like in this case.

[sumeethaldankar]

My now sold Civic developed a overheating problem especially with the a/c on.
It turned out that the radiator was clogged due to dust etc and it was removed and cleaned thoroughly. Post that fresh coolant was added and the problem never came back again.

[saket77]

@Vigsom:
Not only for this issue, but the systematic manner in which you describe and go down for the solution is the key to proper diagnosis and hence reliable repair of any issue. Once my superior told me when I was a freshly baked MBA- "Ask proper questions and you will get the answer yourself." Reflects in all your DIYs.

Thanks for sharing. Though never had such issue in my Honda, but I will double check the suction pipe.

Regards,
Saket

[Ashtoncastelino]

Perfect Diagnosis Sirji, I love the step by step diagnosis you perform. I will never forget the call we had months back when my Swift developed a very bad misfire issue and you were on call even post midnight guiding me with your Step by Step Diagnosis !

Take a Bow ! Fantastic find on this Honda

Regards
Ashton Castelino

[anjan_c2007]

Sorry to read about your ordeal. Issues are cropping up with newer Hondas that could be losing on these "niggles" grounds.
These days owners compare Honda with Toyota and vie for the latter for its bullet proof reliability.
Is Honda losing its standing quality wise?
Honda in this survey in the US as indicated is among the crowd comprising habitual niggle affected OEM's.

[ritedhawan]

Originally Posted by vigsom

How the cooling system works

If the dip hose isn't present, the radiator vacuum relief system will not work. Why? Read on

At the cost of sounding repetitive, let me give a brief on how the engine cooling system works.

Nice explanation. Honda cars which are 8-10 years old and bought between 2006-2015; their owners once in a while may have faced this issue. I used to own a second hand 2007 Honda accord 2.4 AT and curiously not only did I faced this issue as brilliantly explained by vigsom. There is another issue I faced: the following picture shows the point where the plastic inlet of the cap connects to the rubber hose. That plastic inlet got broken, and the rubber hose disconnected from the plastic inlet of the cap would do its job of releasing coolant as explained by vigsom. I replaced the plastic cap and refilled coolant as stated by vigsom in this thread to get past that issue. I used to carry a spare plastic cap because I dreaded that issue may come back. One look at the flimsy looking plastic cap actuated me to keep a spare one.

One of the flagrant flaws for which I wholeheartedly blame Honda --correct me if I am wrong here--is the absence of Temp. gauge on some of the Honda City cars. This to me is a glaring miss. The absence of that important piece in the head up display would compel drivers to wait for that Over Heat bulb to light up. The fact is: had there been that gauge in place, any discerning driver would immediately figure out by that gradual moving up of the temp. gauge needle that something is amiss. But due to the lack of it, drivers have to wait for that light bulb and as far as I am concerned the damage is already done. I am happy to say that both the previous 2007 Honda Accord that I used to own and the one that I own: 2008 Honda Accord have the temp. gauge. Any slight movement of the Temp. gauge needle above its standard mark and I would pull over to start my diagnosis. This luxury --for the lack of better word-- is not afforded to those Honda City drivers.

[HondaSport]

Very informative post! Thanks and could use some help/input on my problem explained below

I have a Honda City 2017 petrol and I am having trouble with the operation of the larger of the 2 fans placed behind the radiator.

It seems the ECM is not sending a signal to the fan to start up and that may lead to overheating issues when summers hit (I am in Gurgaon and the winter temperatures ensure overheating is less of an issue).

My limited understanding is that 1 fan kicks in when the temperature touches 100 C and the other one when it hits 105 C.

As a solution while I am looking for a replacement ECM, a local mechanic helped by linking the 2 fans together; I can now see the larger fan also kicking in.

Question - Is this solution acceptable given I do not want to incur the cost of an ECU replacement?! Also, is there a temperature gauge that I can install since the City does not have one, only a warning light.

[sandeepmohan]

Originally Posted by HondaSport

Question - Is this solution acceptable given I do not want to incur the cost of an ECU replacement?

No.

Are you sure the second fan is there to aid cooling of the radiator? Or is it active only when the aircon is running?

I would go to the better Honda dealers and ask them what logic is applied for the operation of the fans. They can give you a clear answer.

Before spending big bucks on an ECM, take your car to a more competent garage and explain your situation.