M13A engine Overheating

Hi All. I would appreciate any ideas on solving this over heating problem.

The Jimny comes up to operating temperature reasonably quick and continues slowly to an overheat situation, the radiator header tank is hot although the heat is not transmitting down and the overall radiator remains cool. To-date I have taken the following action. This obviously suggests there is no flow of coolant.

1) Replaced the therrmostat
2) Removed/inspected the water pump all good. On replacing made sure of drive belt tension.
3) Removed and flushed radiator. Water flows through ok.
4) Replaced radiator pressure cap.
5) Replaced temperature sensor (unlikely but in case)

There is no visible signs of oil or coolant mixing in the set up. I have had my Jimny thirteen years and Know it's little quirks but this one has me beat.

Thank you
Dave

 

I suspect a blocked heater core - temporarily bypass it with a length of hose so that coolant can flow and see if that makes a difference.

On the M-series engines, the thermostat is on the return or cool side of the loop, and it is dependent on flow through the heater to open it, if the flow through the core is restricted, the thermostat doesn't open, so there is no flow through the radiator and the engine overheats.

I know it's a real PITA having only just done mine, but I would take the thermostat out & try again, as replacing it cured mine but you say you've already changed it.

I have not had reason to work on my Jimny cooling system, so the following is based on my classic car knowledge rather than Jimny direct, so those that know please correct anything that's not applicable to the Jimny.

Thermostat
Cooling systems tend to flow hot water into top of radiator, cool water out of bottom and into the engine (correct for Jimny?)
The top flow is held back by the thermostat, so during warm up very little water flows through the radiator as the thermostat is closed. So if the thermostat is closed the top hose will be cool. In reality a small amount of water flows past the thermostat to prevent air lock and allow it to work, so the top hose may get warm. When the thermostat opens the top hose will be very hot, you can tell the difference if you are prepared to hold the hose as everything warms up.
So stays warm - probably a stuck thermostat
Burn your hand hot, something else.

Radiator
Assuming the thermostat is open you should feel heat across the entire matrix. If you can't or it's patchy then it could be a blocked core. If the core flows ok it's still possible on an older radiator for the fins to become thermally insulated from the water tubes, simply caused by corrosion, so the radiator is inefficient. Fins falling off or fin damage can be a sign of this.

The water pump.
They tend to spring a leak before they stop working, but a cooling system that's been run without antifreeze for some time may be corroded. This corrosion can impact the efficiency of the pump impeller, this in severe cases stops the flow through the radiator. Difficult one to evaluate.

Viscose fan.
When you start a Jimny from cold ( with Air conditioning fitted)  the Air Con fan will spin, after about 30 seconds it will slow down. This is because the viscose fan coupling is still engaged from the last use, the connected cooling fan draws air through the radiator, hence the AC fan spins in sympathy. As it disengages as the engine is cold, it's stops spinning the cooling fan, hence the AC fan stops spinning.
If you don't see the AC fan spin (AC off!) it's possible the viscose coupling is not working as it should. This can cause overheating, but you radiator should still get hot. This fan spin only applies if you have driven it (upto operating temp) beforehand, let it fully cool (overnight) and start it from cold.


I take it it's not loosing any coolant? If it is then that's possibly something else.

Thanks for your quick response guys.

Scimike your understanding of water circulation direction through radiator etc is very much inline with mine (retired heavy truck fleet engineer) however I was aware the M13A engine thermostat is down flow of the radiator as Fordem has stated.

What I did n't know is the thermostat opening is reliant on water flow through the heater matrix. Considering the high temp in my system I must admit I have been surprised by the only mild heat blown into the cab area. So may be that's the answer.

Need to get my head around what happens when you close the heater core control though (summer use)

Dave

Ah !

Had n’t realised the heater matrix was permanently open flow.

Can I ask what action you took in regards to head gasket failure. I have exhaust gasses in my coolant and everything points to the head gasket.
Did you replace the gasket? Or did you do something else such as a sealer or even an engine swap.
My Jimny has over a 130,000 miles on the engine and my dilemma is get rid or throw more money at it.

Sorry folks I that I have n't given a update of Fordem's diagnoses; been away and now trying to catch up on things. Fortunately I have a big old Volvo that is standing in for the Jimny.

Love the old Volvo but it cant do Jimny's job.

I would definitely go the engine swap route if the head gasket has gone on a high mileage 1.3. Its very little extra work or expense for a very worthwhile upgrade.
 

I'm assuming it's not losing coolant/boiling over?

You say you have a lack of heating in the cab, try hitting the heater matrix box firm but gently with rubber mallet and see if you can
get some heat going. If you can this probably means it's blocked, contributing to the over heating.

Mine was doing this too, which ultimately lead to the head gasket going slowly, boiling the coolant too.