Do RF900s & several other bikes run too Cold?

[F5 Dave]

Four strokes run best at an optimum temperature. If cars are run without their thermostat they don’t run as well & chew gas. Many bikes seem to run pretty damn cold. The RF for example has a 76.5 deg thermostat with 5 holes drilled in it. Why is this??

Perhaps they are sent to several markets where they are prone to getting too hot in townwork so they open the thermostats earlier in an attempt to combat this. In good ol’ NZ it’s probably a bit cooler than Spain so there may be some room for improvement.


OK. I have fitted the hotter thermostat. It fits & I took it for a test ride last night (aren’t I good to you?). OK I was curious. It warmed up quicker to almost the first mark but stayed there. The original got to 1mm below it esp. when on the motorway. Then after a few min it crept up to 1mm above the mark. It is definitely running at a hotter setting at about 1/3 on the temp gauge instead of 1/4.

Is it running better? Well this is only a short run but it was going great. It was a bit of a cold night so it may be the bike was responding to having a rich mixture & the fact I have advanced the timing a bit. But it does seem to idle a bit smoother. Early days but worth a try.

The magic part No. is TRIDON brand (available at local servo probably)
TT2003-195 & is 91 deg. If you dummy fit it in you will find a possi it will fit despite being centrally positioned instead of offset like the original. This will have the writing on one of the arms upwardsish. DO NOT FORGET to drill a small hole say 3.5mm at the top once you have worked out where it will sit. Check it is unobscured. Fit the original rubber outer ring. Put back together & fill. Run & check water level again.

Incidentally I got this idea from the Factory website, so I am assuming he knows what he is talking about. He reckons some bikes run so cold they are a bit lean after a decent ride & makes the carburetion uneven, though it is hard to determine what bike he is talking about; he states ALL Suzukis of that era are afflicted.

[Motu]

A factory thermostat with holes drilled in it sounds suspect,a cover up for problems in another market?

I can't find a TT2003 in my Tridon book,but that doesn't mean anything. Motors like to run real hot,much hotter than most people realise,but sounds like you are onto it.I find it hard to get mechanics to pick up on open thermostats,they think running cool is cool,but it's not and leads to all sorts of problems,specialy if it is computer controled - if the ECU gets a cold running signal it will respond accordingly,with more fuel and raised idle for a start.

And just from a thermodynamics point of view a hotter running motor is better - heat flows from hot to cold,and the bigger the differential in heat the better the heat transfer.A water cooled engine (actualy it's not water cooled,the term is indirect air cooling) runs at a stable temp which means it doesn't run at either extremes of temp,but then it's not designed to,so when it does expect problems.

The old British bikes had their carbs bolted directly to the cyl head and had really erratic idles - if you were stuck in traffic it would start to idle faster and faster as the carbs warmed up...down to the next set of lights and it would stall because the carbs cooled down - you could never get it right.

[F5 Dave]

Yeah maybe it’s misprinted on the label or a new model (I got it from the local Appco shop). On the back of the packet there is a TT203-195 fits a Commodore. Either way it’s a smidge under 44mm 91 degrees & a compact design.

[madandy]

Interesting! I always new my bike was running too cool now I feel I was right...My guage sits on the C mark at all running speeds and only warms up near or slightly past half way sitting in traffic for a few minutes...Do you reckon Tridon TT2003-195 will fit my 400?

My engine also suffers from poor carburation after a good work out-surging around 4-5000rpm on part throttle ...it does not do this untill its been ridden hard for a while.

Cheers F5 Dave

[F5 Dave]

I’d say it was definitely worth a try for $18. Drain the coolant (needed replacing by now no doubt as the anticorrosion properties are the important bit).

Pull the old one out & if it is 44mm without the rubber then likely it uses the same thermostat (lives under the RHS fairing by the rad filler). This should keep things a bit more consistent with a warmed engine.

[Big Dog]

Pay also to keep in mind that oild that does not reach full operating temp at least once a week will deteriorate quicker than oil that does. This is because at full temp certain bad things (like moistre from allowing your bike to cool) evaporate instead of allowing the additives to seperate.


I found also that japanese coolant runs 10% colder than NZ sourced replacement that meets manufacturer requirements. (same brand same rating as the handbook recco'd)

[madandy]

Well I took the RF for a hard ride all the way into Mt Albert, Auckland yesturday to pick up a new riding jacket and on the way home the temp. guage actually rose to just under the half mark and sat there all the way home! Like it just needed a long, hard run at speed to warm the thermostat up properly and get it working.
My normal daily is 50kms,return, open road at 110-120km/h.Yesturday I was cruising above that with regular squirts up around double the limit.
I'll keep an eye on it tommorrow riding to and from work and see if it's working right again-if not I will try another thermostat.

[k14]

I have the same problems on my CBR. The maximum i have ever seen the temp guage is half way and that was on a really hot day (around 24) riding round town and stopping at traffic lights etc.

In my trip from NP to Christchurch, it never got above the lowest mark. Probably not the best for the engine.

[F5 Dave]

OK strange fact:
Went for a ride with a friend who has a different model RF. It heats to the same position on the temp gauge as mine now does with the new thermostat. I assume one of two things: a: The temp gauges are inaccurate, or b: in some models they were having overheating concerns so they fitted colder thermostats so in town work they had further to heat up.

[SPman]

Dave, has the YZF got a thermostat? Coz mine barely registers on the temp gauge unless Im in traffic!

[merv]

OK strange fact:
Went for a ride with a friend who has a different model RF. It heats to the same position on the temp gauge as mine now does with the new thermostat. I assume one of two things: a: The temp gauges are inaccurate, or b: in some models they were having overheating concerns so they fitted colder thermostats so in town work they had further to heat up.

That sounds strange because all said and done whether the bike overheats or not would be a function of the size of the radiator and how good the fan and water pump are and I doubt it would matter whether you had a 76 deg thermo or a 91 as it would go from 76 to 91 in a matter of next to no time if you were stationary in heavy traffic (Auckland, Los Angeles, London or wherever) and once it gets to about 110 - 115 its frying and the thermostat would make no difference to that.

Sure though if the engine is running cold it would do it no good at all and the thermostat is there to let it warm up quick and keep it running as close to an even temp as possible.

I noticed the back of my wife's Honda Civic was getting a bit black and she hadn't said anything to me, I have a drive and cruising down Ngauranga Gorge the gauge damn near dropped off the bottom of cold. Cripes in with a new thermostat as the EFI would have been squirting juice in to compensate for the cold engine which was then blowing a lot of it out the back as soot. So wasting fuel and a bit hard on the motor.

You have done the right thing to warm your motor up.

[Motu]

Get a non contact infra red thermometer,takes all the guess work out of it - you can see what every little bit of your motor is running at - can even do it on the move,well,if you can multi task like a sheila.

[FROSTY:Me]

I know the old xj750's came with or without oil coolers depending on the market they were intended for. If the cooler leaked or got bent we would just pull it off. Never seemed to make the slightest bit of difference.
It would figure that the stat on a water cooled bike might be set for a warmer climate. Once the bike got to opperating temp it shouldnt make a difference but it would seem reasonable that they might take longer to get hot.

[F5 Dave]

The std thermostat on my RF (& others have reported this) has 5 holes drilled in it. This would seem to aid flow but delay warm up. This is not good practice at any rate so I feel this is a bodge to try to remove a symptom rather than affect a cure.

76.5 degrees rated on the thermostat is very cold for a 4 stroke. If you are sitting at the lights & start from 10 degrees colder with a freer flowing thermostat then it will take longer to heat & thus overheat. This is a bodge though, a gruntier fan that comes on earlier would be a better course of action.

Better explanations on a postage stamp please.

SP. For years I thought the YZF SP had no thermostat so I have been taping the radiator esp. in winter. A search on the internet parts fishe for the std R model shows there is a housing & it is hidden at the back of the cylinder beneath the carbs. Looky there it is when I go for a look.

The question is does it contain a thermostat or as a race model did they leave it out?

I have a 82 degree one from an Exup to try, but as I have been fitting the new bodywork up on the SP & Racebikes etc to tend to I haven’t gone digging.
I might tonight, but then again I have to make a new subframe for the new tailpiece. If you get there before me let me know huh?

PS my coolant gets pretty grundgy on the couple of times I’ve changed it. The last time I took a while backflushing the system several times with a hose, I suggest you do the same. Thinking about it, the reluctance to clean out may indicate there is a thermostat. Make no mistake 4 strokes do have an optimum temperature & overcooled is not good.

[pete376403]

Leaving the thermostat out can cause a motor to run hot. I encountered this a long time ago while working on a Mini7 - pissy little radiators and cast iron engines that heat up fast and stay heated up. The thermo had been removed to "improve cooling' but made it boil. Reason was there was no restriction to water flow within the engine, so the water never had a chance to pick up the heat and transfer it to the rad. Inserting a restrictor into the thermo housing (the washer was the outer ring of a thermostat) got the cooling back under control.
Electric water pumps would be better in a lot of cases as the pump speed could be varied as the cooling requirements change. With an engine driven pump, it's turning too slow when needed, say riding slow in traffic, and too fast when not needed (blatting down the motorway with a good stream of air through the rad)