Thundercat Running Temperature

Hi Guys!

Okay so I'm looking for a little advice/information if I may please?

I have a Thundercat which, like most Thundercats, runs well into the red on the temperature gauge before the fan kicks in. It has even gone as far as boiling over before now. The system holds pressure and there are no blockages.

I am going to change the radiator thermo switch for a lower temperature range (current switch operates at 105C, turns off at 98C) in order to reduce the risk of this happening again.

What I'm struggling to find however is the optimum running temperature for this engine in order to select a suitable temperature range.

So, my question to the forum is what is the optimum running temperature for the Thundercat please?

Many thanks,

Lee

Up until last week I had 30% of the rad covered over as Cats run cold for most of the time. The fan will only cut in when the gauge is in the red, but it soon cools down. The boiling over sounds like you had to much water in the header tank. During the winter I have 75% of the rad covered to allow the bike to run warmer. In this warm weather the bike runs at about 65/70 degrees until heavy traffic and then it slowly gets warmer until the fan cuts in (three times in the last few weeks, more than in the last three years). Don't bother changing the thermostat as the cooling system by passes a large amount of water through the oil cooler so it will never get warm. My Cat runs far sweeter at cooler temps than when it's hot, like me it gets short tempered when stuck in traffic, but other than a few more rattles and more of a snatch to the throttle when hot it's never done any damage to the bike.

Hi Lee, welcome.

How often are you going into the red and under what conditions? Mine only did it in London's stop/stop traffic, was jokingly going to write a label with London on it and stick it over the red zone

My Tracer will get hot far quicker than the 'Cat ever did, the fan is forever coming on.

Coolant boiling doesn't sound good, you not got an airlock maybe? I never found a problem with the standard settings for the fan.

Hi there,

Thank you for the warm welcome! .

Okay so there are no airlocks.

Radiator cap swapped with my other bike no difference.

Thermostat tested on the hob with a thermometer and all is good.

Fan kicks in no problem when shorted.

Temperature sender unit under reads.

So, I reckon this is a 2 fold issue.

1. I think the thermo switch is activating either at too high a temperature, or not at all.

2. Because the temperature indication under reads, the bike is actually a lot hotter than it would suggest on the dial, so the temperature sender is suspect. I had originally thought that the coolant
was boiling just under 100C which would suggest little or no pressurisation.

I've seen on various forums that a lot of people fit a manual switch to the radiator fan circuit and mount it down to one side of the bike. I don't want to do that as it sounds faffy and likelihood is I'd forget I've turned it on.

I figured that, if I'm going to replace the thermo switch anyway, then may as well kill 2 birds with one stone and reduce the activation temperature. It won't have any affect on the temperature of the engine whilst moving as there will be forward airflow and that was never an issue anyway. It only ever gets hot when stood still.

My theory is that by cutting the fan in 10 degrees or so earlier, it won't go into the red in the first place, ignoring the fact of course that the gauge lies anyway but since it is only indication I'm going to leave it be.

Ill have a look into it and post what I find.

Perhaps the sender is defective. There aftermarket ones available like this one.
sender switch

Remember that water mixed with ethylene glycol has a slightly higher boiling point than 100 degrees C (you do have a 50/50 mix)? Its also tends to get higher as the pressure increases, so if it boiled it would suggest it was a fair bit over the target temp range....

Are you sure the water pump is okay? Perhaps the coolant is static and simply not flowing through the system?

Welcome to the forum Lee.

Sorry to hear you're having an issue with coolant boiling over. here's a [You must be registered and logged in to see this link.] to the workshop area and a related subject.

Hope you manage to figure it out soon and inexpensively

Cheers
Tel

Hi & welcome. The thermostat is fully open at 68 so they do run cooler than most engines. Try draining the cooling system & flush through the system with a hose pipe & refill with fresh coolant. It might never of had a coolant change unless you know the history of the bike.

Paul