Overheating lamp comes on on motorway driving or in heavy stop/start traffic

[Ted]

Hello,

The red overheating lamp on my 2013 Jazz has come on a few times in the past year but the garage has no idea what the problem could be.  Most recently (last Sunday) I was driving in light traffic along the M25 anticlockwise towards Gatwick Airport when it suddenly came on at the M23 junction. I'd not been going much over 2000 rpm and 65 mph. Anyway I pulled over in one of those emergency laybys and let the engine cool down, although there was no steam coming out, the coolant was only halfway up the overflow tank, and the engine didn't seem overly hot. After about 10 minutes, I started the engine and the lamp had cleared. Thereafter, I hobbled along at 50mph to the next junction before returning home via A roads. On the way back, I noticed the lamp came on again when going uphill but would clear when coming back down.

The other two times it came on were briefly when driving on the North Circular in February, and before that in November under very similar circumstances to Sunday when I was on the M23 (again) heading towards Brighton.   

I explained all this to my local garage but they told me they'd never seen it happen with a Honda Jazz, and that I'd need to bring the car in with the lamp on if they were to catch it in the diagnostics. They did check the coolant level and the dipstick but found no issues. I called the local Honda service department and was told me pretty much the same thing (also wanted to charge me £150 for the diagnostics test!)  Problem is that I only go for long drives, where the lamp is likely to come on, on weekends when the garages are shut.  I don't want to risk it.

[TL;DR] 2013 Jazz mk2. Overheating lamp sometimes comes on under pretty normal driving conditions. Local garage and Honda Service can't tell me why.

Any advice on what the problem could be, and how I might go about getting it fixed? Wife was not best pleased when it ran aground last weekend!

Thanks in advance.

Ted

[DV]

Hi Ted,

Did the garage remove the cap from the radiator and check the coolant level? (not only in the overflow)


The below ideas are from Chat GPT:

Potential Causes

Low Coolant Level: If the coolant level is low, the engine may overheat. Check the coolant reservoir and radiator when the engine is cool.
Coolant Leak: A leak in the cooling system can lead to insufficient coolant. Inspect for visible leaks or stains under the car or around the engine bay.
Thermostat Malfunction: A faulty thermostat can fail to open, preventing coolant from flowing through the engine properly.
Radiator Issues: A clogged or damaged radiator can impede coolant flow. Look for signs of clogging or external damage.
Cooling Fan Problems: The electric cooling fan may not be working correctly, which is critical for maintaining temperature at low speeds or when idling.
Water Pump Failure: A failing water pump cannot circulate coolant effectively.
Air in the Cooling System: Air pockets can prevent proper coolant circulation. This can occur after a recent coolant change or if there is a leak.
Faulty Temperature Sensor: The temperature sensor itself may be providing incorrect readings to the car's computer.
Head Gasket Issue: Though less common, a failing head gasket can cause overheating.

Diagnostic Steps

Check Coolant Level: Ensure the coolant is filled to the appropriate level in both the radiator and the coolant reservoir.
Inspect for Leaks: Look for any visible signs of coolant leaks around the engine, under the car, and on hoses.
Examine the Thermostat: If the thermostat is stuck closed, it will need to be replaced.
Test the Radiator and Fans: Check if the radiator is clogged or damaged and ensure the cooling fans operate correctly when the engine heats up.
Check the Water Pump: Look for any signs of leakage around the water pump and ensure it is circulating coolant properly.
Bleed the Cooling System: Remove any air pockets from the cooling system by bleeding it according to the manufacturer's procedure.
Check the Temperature Sensor: Verify the temperature sensor is functioning correctly with a diagnostic tool.
Look for Head Gasket Symptoms: Symptoms like white smoke from the exhaust, milky oil, or coolant loss without visible leaks can indicate head gasket issues.

[olduser1]

Has the coolant ever been changed, same for thermostat.
Any signs of leaks where parked. Dies the heater operate as normal.
Other replies have more details & good suggestions.
Not heard of this before on UK Jazz.

[Ted]

Has the coolant ever been changed, same for thermostat.
Any signs of leaks where parked. Dies the heater operate as normal.
Other replies have more details & good suggestions.
Not heard of this before on UK Jazz.

Now that you mention it, the heating was extremely weak when I bought the car back in 2016. I finally had the heater matrix replaced last year it's been working very well since then. I guess the coolant was drained and refilled at that time. But I wonder if there is still some gunk in the pipes that's been impeding the flow and maybe caused the blockage of the original heater matrix. I'll give the garage a call and ask them about that. Thanks for the hint!

[Lord Voltermore]

I dont know about the Mk2 Jazz but some cars are very susceptible  to air locks  unless the coolant is refilled in a specific way  . It often has to be refilled VERY slowly, as a dribble  rather than  being glugged in. 

These airlocks can be very persistent  and prevent the coolant circulating freely.  For instance at times the water pump may be trying to pump compressible air rather than a liquid. 
 
Even if things seem to settle down again by itself  its a good idea to get the system, and possible causes checked out by an expert  .   In the 'good old days'  loss of coolant could cause the temperature gauge   to go very high,  then suddenly drop to a low reading.  But far from being a good sign this meant the coolant levels had dropped so low the temperature gauge was no longer immersed in coolant and major engine damage was imminent.
 

[Westy36]

(also wanted to charge me £150 for the diagnostics test!) 

Hey Ted. For that kind of money you could buy a diagnostic tool, such as Autel, and see if there are fault code to help with diagnosis.

As a work around, get the heater on max hot setting. The heater matrix then acts as an extra radiator and can help with the problem.

The manual if you need it is here https://hondafitjazz.com/manual3/index.html - it'll give you all the info you need on where components are and how to replace if needed. If you use a garage, at least you'll have an idea of whats involved to see if any quotes are reasonable.