Controversial but it works great

2417 Views 43 Replies 17 Participants Last post by Hawkerjet, 6 mo ago

Biggs3118

Discussion Starter · 6 mo ago

Long explanation, please forgive me.

It finally got cold here and I've been riding the highway in 40degF temps the temp gauge would 'barely' see 1/4(I don't like that, plus it's not good for the engine to run that cool).

I'm from AZ and ride when it's 110degF so ya, 40degF is 'cold' for me. I also have a lot of scare tissue from tons of surgeries that's blocking blood flow.

By the time I make a quick stop at a store and return to the bike it would be nearly completely cooled down and I'd have to wait for it to register on the gauge again before hitting the road(I always let my bikes warm up). Note: I do NOT have a Tbob on this bike.

I decided to experiment with a typical mod that is often seen in the 'big rig' community during cold weather. After making some basic BTU calcs I came up with this, it blocks exactly (1/3) of the radiator surface area.

Hood Grille Automotive tire Automotive lighting Motor vehicle

I realize it looks basic but keep in mind it's experimental. There is a reason it's on the bottom.

This simple mod allows the bike to now come up to 1/2 on the temp gauge when riding in the cold (where I like it to be for efficiency sake among other reasons) Same goes for hot summers, I like it to run right about 'half' on the gauge.

The engine obviously maintains it's heat longer after shutting it off to run into a store. I haven't had to wait to let it warm back.

Coming up the mountain on the way home it still sits at HALF on the gauge.

It's not good for the engine to be loaded hard while running 'too' cool.

I'd also like to point out that I don't even have to 'top off' the oil between changes on this bike(doesn't burn a drop) even after 6hrs of 4500-5000rpm on the highway.

Not trying to create drama, just thought I'd share my 'simplistic' solution. If it works for 'semi trucks' it could too work for the KLR.

Let me be clear, I still believe having a Tbob is the ideal setup. I just don't have one at this point. I also believe that 'always' letting the bike 'warm-up' before getting on it has protected this engine.

Thanks for reading my long post, best wishes and ride hard/often.

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Timlang60

· #4 · 6 mo ago

This is a great hack - even a couple of strips of duct tape would do in a pinch! I'll just say I have a 'Bob installed and ~3 weeks ago I made the 210 mile trip from Mayo Clinic to home at ambient temps that started at 34° and ended at 28°, and the temp guage never budged off of 190° indicated. Except for extended stops in jammed up traffic, I see the same during temps into the mid/upper 90s during the summer - the temp comes up to low operating range while I'm strapping on my helmet and putting on my gloves, it's at normal temp within a mile and a half of easy riding, then it doesn't budge from there except as mentioned above. If I ever buy another KLR, it'll have a t-bob installed within days.

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Timlang60

· #13 · 6 mo ago

DPelletier said:
Engineers aren't infallible; 165 deg. is too cold. though raising the minimum operating temps isn't the primary benefit of a Thermobob. I do agree with removing the temp gauge.

Dave

I think you're wrong. Engineers ARE infallible, that's why no KLR ever burns oil, and you don't ever have to check it! 🤣

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Timlang60

· #22 · 6 mo ago

StarfuryTH said:
I just said it was an old hot rodder solution which gives some extra overhead before the engine overheats. It won't cure a constant overheat issue under normal running conditions.

Sort of what they're doing with a top fuel engine that doesn't even have a cooling system - using the entire block and head as a giant heat sink over brief periods of intense operation.

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Timlang60

· #28 · 6 mo ago

klr406 said:
It could easily be my mechanical ignorance, but some of the posts in this thread, particularly those mentioning "over-cooling" and "operating temperature" see to imply that the stock 165F thermostat is going to determine the temperature of the coolant in the cooling system. Isn't this just the temperature at which the thermostat is supposed to open and let coolant from the radiator into the block? If so, it seems like this thermostat is only going to allow coolant to flow through the block earlier than a 195F thermostat, but it doesn't determine fully-warm operating temperature, i.e. coolant may begin to flow through the block at 165F, but the coolant temperature will continue to increase as the bike continues to warm up.

Actually, the thermostat controls the temperature at which coolant can flow out of the block so for all practical purposes, it sets the max engine temperature. The only way the temp will rise above that is if the radiator has too little surface area to shed heat at the same rate the engine is making it, given ambient temps and the amount of/speed at which air is flowing past the cooling fins. Additionally, in a simple, basic cooling system like a KLR, the actual average internal coolant temperature will be somewhat cooler than that and will include fairly severe and abrupt downward swings followed by a slow climb back to thermostat temp because, without a bypass, when the thermostat does open the coolant that enters at the bottom of the block is 100% from the radiator, which has just been sitting there not moving since the last time the thermostat opened and may have called off by 30, 40, or even 50° or more. The delta between the coolant temp leaving the motor and the coolant temp flowing in will tend to be larger under cooler ambient temps and lower engine loads - colder air removes more heat, and lower engine loads extend the periods between thermostat openings, giving more time to cool. Not incidentally, this is the issue that the Ther-O-Bob seeks (and largely succeeds) to address. It won't raise or reduce max coolant temp, the thermostat still does that. What the 'Bob does do, with its bypass system, is reduce the coolant temperature delta (difference in temp between coolant input and output), making for an engine that runs at a consistent temp, or at least within a much smaller range.

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Timlang60

· #31 · 6 mo ago

klr406 said:
So the thermostat will open when coolant in the block reaches 165F, but that's the only limit associated with the thermostat, meaning the coolant temperature can climb from there without reaction from the thermostat. I thought I read somewhere (sorry, can't remember where, maybe in a KLRforum thread) that the Tbob only increases fully warm operating temperature approximately 5F but that temperature is possibly 30-40F above 165F. If that's true, the thermostat still does nothing more to affect operating temperature after it has opened. Are you implying that the stock operating temperature of the KLR varies to either side of 165F regularly, causing the thermostat to cycle between opened and closed?

Yes. The thermostat in every water cooled internal combustion engine that operates using a wax capsule (which is every engine coolant thermostat that I'm aware of) is in an open or closed state, there is no variable attenuation. In a modern vehicle, where a computer is monitoring or controlling every variable of engine input and operating conditions, they probably could put in a computer controlled gate that would read ambient temp, fuel input, engine load, speed, etc., and compute how far to open the gate to provide just the right amount of coolant flow - and I wouldn't be surprised to find out that such systems exist on exotic, close tollerance, high powered engines such as you find in F1 cars - but thats a lot of complexity and cost for no real gain in vehicles for which a standard thermostat and a properly engineered bypass system have proven more than accurate.

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Timlang60

· #35 · 6 mo ago

klr406 said:
I appreciate the back and forth on the Tbob though I'm sure it's been kicked around all over the forum before. I'm trying to decide if it's a mod I want, and I'm not sold yet, but this is helpful.

Here's an animation on YouTube that shows how a thermostat in a cooling system with a proper bypass opens and closes to redirect water. It doesnt explain the 'hows' of a wax capsule thermostat, but you can find that here if you're curious.

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