Overheating, I am stumped

When you put the A/C on you add a little bit of extra load to the drive the compressor, so that adds a bit of heat, but unless your A/C compressor is starting to seize it wouldn't make much difference.

The heat that the A/C takes out of the car is lost in the condenser which is in front of the radiator so reduces the efficiency of the radiator and that is usually why the engine runs hotter with the A/C on.

If you have a head gasket issue then you would normally see one of the following:

Oil or bubbles in the water;
Water vapour in the oil (or emulsifying);
One of the spark plugs wahed clean.

The fact that out on the highway it gets hotter suggests it might be airflow, I know the engine is working harder, but you should have airflow over the radiator and this should compensate.

So how long have you had the vehicle and what, if anything, changed when it started to over-heat?

It could also be mixture, if it was running very lean, that would cause it to over-heat.

Does the M18a engine normally run with a bigger radiator (someone from the forum might know)?

What about a build up of debris on the outside of the radiator or even a coolant flush (going on what you say you have probably already done this)?

Is the water pump belt slipping (any squeal?), giving poor circulation or is the water pump starting to sieze up (I see the water pump is new)?

If all this fails the specialised Whatsapp group might be your best bet.

How does the M18 donor vehicle radiator compare to the standard Jimny 1.3 radiator in size and cores?

​​​​​​Has anyone checked to see if you simply need a larger capacity radiator to cope with the larger capacity engine?

It's just a Sherlock Holmes inspired question based on the fact you have changed everything. It may simply be the standard radiator operation is marginal on the M18 and some conversions are just about getting away with it. I don't know the answer unfortunately, but hope someone has the comparison information as I would also be interested.
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Thank you for your reply Roger. I replaced the Visco, referring to the viscous coupling for the fan, it appears to be working fine

Thank you for the comprehensive reply!

If you have a head gasket issue then you would normally see one of the following:
Oil or bubbles in the water;
Water vapour in the oil (or emulsifying);
One of the spark plugs wahed clean.
It displays none of these symptoms and we performed a chemical test that indicates that there are no gasses present in the radiator.

The fact that out on the highway it gets hotter suggests it might be airflow, I know the engine is working harder, but you should have airflow over the radiator and this should compensate.
That was my initial thinking, I then cut out allot of the replacement bumper. This did help quite a bit so there must have been an airflow problem of sorts. I can't cut away any more of the bumper without risking structural failure of the bumper

So how long have you had the vehicle and what, if anything, changed when it started to over-heat?
I have had it for a few years. The problem started when I upgraded the engine from 1300 to 1600. After being unable to solve the issue we put in an 1800 as we thought there my have been an issue with the oil pumping system.

It could also be mixture, if it was running very lean, that would cause it to over-heat.
Is there any way to adjust this as this? I was under the assumption that the ecu does this automatically

Does the M18a engine normally run with a bigger radiator (someone from the forum might know)?
According to what I have read they use the same radiator, but would love to hear from those in the know

What about a build up of debris on the outside of the radiator or even a coolant flush (going on what you say you have probably already done this)?
Yes this was checked, as I say the radiator and condenser are brand new,

Is the water pump belt slipping (any squeal?), giving poor circulation or is the water pump starting to sieze up (I see the water pump is new)?
Yes, waterpump was replaced, I haven't noticed any belt slippage.
 

Thanks for your reply!

How does the M18 donor vehicle radiator compare to the standard Jimny 1.3 radiator in size and cores?
The local guys here have done a few of these upgrades and always used the standard radiator without an issue. I would love to hear if there is a radiator upgrade, that may solve the issue,

​​​​​​Has anyone checked to see if you simply need a larger capacity radiator to cope with the larger capacity engine?

It's just a Sherlock Holmes inspired question based on the fact you have changed everything. It may simply be the standard radiator operation is marginal on the M18 and some conversions are just about getting away with it. I don't know the answer unfortunately, but hope someone has the comparison information as I would also be interested.
Thanks, yes I actually hope there is an upgrade radiator that can fit. Think it may help

Don't get me wrong, it looks like radiator and airflow to me, but there could be other issues.

'It could also be mixture, if it was running very lean, that would cause it to over-heat.
Is there any way to adjust this as this? I was under the assumption that the ecu does this automatically'

The ecu does do set the mixture, but bases this on
- 'maps' of how much fuel/air is required for a certain rpm
- the MAF sensor (how much air is entering);
- all fine tuned by the O2 sensors.

In theory the bigger engine will take more air for any given rpm and therefore need more fuel, but the 1.3 stock ecu might have 'maps' which are fine tuned for the 1.3 and these need to get over-written, this usually happens over a few hours of driving. I am not sure if others have changed the ecu when changing the engine or even if it is required but the stock ecu might not be able to cope well with the bigger engine.

What about timing? If you have pre-ignition that can cause over-heating?