4BL Overheating Problems

[dominik22]

Hello all and greetings from Germany,

i have a weird problem with my 4BL.

The stock temp gauge broke off in the head and would have to be drilled out, thats why i installed a Temp Gauge on the upper Radiator Hose (the T fitting Type) and am reading temps up to 115 celcsius after 5min run time.

Things i checked:

Water pump impeller looks fine and spins with the engine
All hoses flushed
Radiator flushed and cleared
Thermostat removed
Hose from thermostat removed and started the engine to confirm the flow of water.
Jetting on the richer side

When i put 2 temp probes in the upper and lower radiator fins i get a temp difference from upto 40 degrees, so the rad is functioning
But the water coming into the rad is getting too hot

When i start it and take off the temp is stuck at around 30-35 degress for a while and then suddenly skyrockets

No exhaust fumes in the coolant
No overflowing expansion tank

I am lost at this point

Does anybody maybe had the same problem and can help me here ?
I would really appreciate it

[Calum]

These engines aren't exactly known to run ice cold, but certainly not 130 celcius.

If you're confident that the temperature sensors are accurate then the only thing I can really think is head gasket is blown and is superheating the coolant directly.

This is normally evident with oil contamination in the coolant. Normally sticking your fingers in the radiator your fingers come out black.

The alternative is things like cracked head etc and at those temperatures I am not surprised.

My DTR used to run at 110 in idle traffic and I decided that was too hot. I run twin rads and removed the thermostat, now sits at 60 creeps to 70.

[dominik22]

Ive checked the coolant, drained it, flushed it etc
Even with a co tester for blown headgasket and nothing came up.

At first i tought the headgasket is restricting flow, since its got a new cylinder and piston
But i checked this too and flow seemed sufficient

[Calum]

Is the fueling correct? What's the colour of the spark plug?

[dominik22]

On the richer side
Since im still breaking in the new cylinder and piston
Overheating helps seating those rings better

[Calum]

Richer would cool the piston crown making it run cooler. Too rich and risk having bore-wash.

Is the water pump definitely flowing appropriately? Unfortunately the cogs are nylon and although I've heard them failing, it's certainly a possibility.

[dominik22]

Found the problem

Turns out you can mix up the base gasket and put it on the wrong way, blocking the coolant passage.

Luckily no damage to cylinder or piston

[Calum]

@dominik22 Okay thanks for the update as I was struggling to understand why it was overheating. As I say, they're not known to run cool, but I've not heard too many horror stories about excessive overheating.

[HOTSHOT III]

@dominik22 Well you're doing better than me, once I was rebuilding a TDR250, thought I'd finished and then rode to my friend's house without connecting one of the carb warmer hoses! As you can imagine the temp gauge skyrocketed, luckily it wasn't far and we were able to top it up so I could get home.