No more RICH EFI in the cold! (t-stat install)

80 replies to this topic
  • tech24

Posted January 01, 2011 - 09:45 AM


As some of you know an EFI system with no way of maintaining a constant coolant temp will not perform consistent and run very rich in cold ambient temps. In some situations can cause drivability issues and possibly contaminate engine oil with excess fuel. IMO an FI systems needs and thermostat of some kind to function properly and efficiently. Sure its cheaper to cover your radiators but I demand perfection so I did some reasearch and found and installed an EPIC bypass thermostat.

It seems to work well an maintain an ECT of about 170 degrees as designed. I need to put it to the real test on some fast wide open areas in extreme cold but I see no reason for it not to function as expected.

If anyone is interested here is the place I got it. http://www.epicincor...y=11&ItemKey=15

Its expensive and designed for shifter kart racing. The only problems are the sales license is expired for the website and I took the last one he had in stock. If anyone wants one they can call the number on the website, Erik seems like a very nice guy to deal with and was helpful to me. Or PM me and Ill call him and if enough are interested he may put in an order. Its off-season so I don't know fior sure.

Kit comes with bypass t-stat and housing, hose clamps (too large but usable), and a 3/4 in tee (too large scraped it for a 5/8) Its bigger and heavier than it looks.

Ok here's some pics

Heres the unit, its anodized aluminum very nice quality

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Here's where it needs to go, its a tight fit and my radiator is bent back about a 1/2 in so I had even less room

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Here I mocked it up with some 3/4" heater hose from head to raditator and 5/8" heater hose tee'd into the return hose.

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Now that I got my final hose lenghts figured out its ready for permanent install. I used gates heater hose for everything expect for the 90 degree at the water pump. There I cut the factory hose. I also wet sanded the white lettering off the hoses so it will look a little better.

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I let coolant temp reach 180 then turned a fan on the radiator and the temp droped and maintained at about 170

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The way this works is: Hot coolant from head enters housing. If its temp is below 170 degrees it goes down to the water pump and bypasses the radiators. At 150 to 170 degrees the thermostat opens partially and allows blended flow through the radiators and bypass. At 170 degrees its fully open and full flow is going through radiators. This can be installed year round with no issues. Thanks for lookin!

Edited by tech24, January 03, 2011 - 04:52 AM.

  • Gunner354

Posted January 01, 2011 - 10:22 AM


eBay has ktm 300 thermostats for $40

  • tech24

Posted January 01, 2011 - 10:42 AM


eBay has ktm 300 thermostats for $40

I looked into using a KTM thermostat. 2 Stroke normal operating temps are much lower like around 125 degrees as oppossed to 160 to 200 degrees. I was considering a ktm 450 t-stat but the inlet and outlet fittings are on the same side and would have required some creative hose routing. It would have cost over 100 bucks anyway but it is usable.

  • Gunner354

Posted January 01, 2011 - 11:05 AM


Ktm four stroke thermostat is 70c. Install the 4 stroke thermostat in the 300 housing

  • tech24

Posted January 01, 2011 - 11:22 AM


Just looked at the 300 setup and I remember looking at it before and I don't know how to make that thing work with 4 different hoses/fittings. Kind of a screwy design. z

There are other options than what I did but it seemed to be the easiest and cleanest setup I could find. Surley not the cheapest but savings wasn't my goal on this one.

Now I'm waiting for some goofball on the trails to ask me about my NOS due to the colors :excuseme:

  • brentn

Posted January 01, 2011 - 03:00 PM


This should be added to the FAQ, what a great writeup with awesome pictures!!!
Glad it worked, unit looks like it may hit the fins with rough riding?

  • grayracer513

Posted January 01, 2011 - 03:37 PM


Good work. I had a feeling that this kind of thing would solve the problem. Thanks for pioneering.

Post your findings after you ride a time or two as to the fuel contamination issue, too.

  • tech24

Posted January 01, 2011 - 06:10 PM


This should be added to the FAQ, what a great writeup with awesome pictures!!!
Glad it worked, unit looks like it may hit the fins with rough riding?

thanks guys! Its not quite as close as it looks in the pics. Its close though and took some precise hose lengths to get it just right but believe it or not it will not move much in any direction I can't physically push it enough to contact anything. Thats one reason I used mostly gates heater hose because they are real stiff. The OEM hoses are flimsy which I could've cut and used but I feel its more secure and stable with the heater hose.

Good work. I had a feeling that this kind of thing would solve the problem. Thanks for pioneering.

Post your findings after you ride a time or two as to the fuel contamination issue, too.

Will do! I want to get back to the state forest trail where I had most of my issues. I guess I'll have to ride around with tuner in my pocket and check it every so often. My only concern was the blended mix we dicussed previously from some coolant going from bypass into the left radiator because the radiators did get warm quickly before the t-stat even opened, however I don't feel it was enough to cause much heat exchange.

  • tech24

Posted January 02, 2011 - 08:28 AM


I'm back at the shop today doing a little more work and maint so I decided to check the t-stat operation a little and I may be a little disappointed. I let the ect reach 180 then rode in circles as fast as I could in the small area out back. I'm maintaing about 140 to 150 degrees. I think it may be due to the dual radiator design and a little bit of backwards flow at times. However it wasn't a very realisitic scenario because there was no load on engine and very little throttle input so not much heat could even build. I also think 150 degrees is plenty warm enough for better efi operation and still should take care of the excessive fuel delievery.

A real testing situation should occur in 2 weeks as I can't wait to ride with all the new goodies I just put on. I'll also get out an infrared thermometer and see what exactly is going on. A restiction in the bypass hose may be in order. Stay posted!

Edited by tech24, January 02, 2011 - 04:25 PM.

  • tech24

Posted January 03, 2011 - 05:06 AM


Another update: Came in this morning fired the bike up and both radiators were warm at about 100 degress ect. So I pinched off return hose to left radiator and it remained cold and right radiator still got hot well before opening temp. So this eliminates the backwards flow theory which was rather difficult to believe anyway. I'm all but convinced that the thermostat element is opening too soon or not remaining closed at all.

Edited by tech24, January 03, 2011 - 05:23 AM.

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  • tech24

Posted January 03, 2011 - 10:03 AM


Okay now im confused. I wanted to verify my suspicion of stuck open thermostat. I completely blocked off both hoses to RH radiator. As before the LH radiator warmed up with the ECT. I could see flow through filler neck. I piched of the large hose going to top of radiator and I still had signs of flow. I removed pliers from that hose and pinched of the hose at the bottom of the radiator and flow stops completely. Is there anyway this cooling system flows backwards unlike I was thinking? It would seem strange to me that this would be the case but its the only thing that makes sense. I guess I can remove hoses and kick it over to check. What am I missing here? I have a hard time believing I have a bad t-stat but I also don't believe the system flow backwards compared to other bikes.

Update: Alright I apologize for my rambling just a bit high strung about this at the moment. I'm supposed to be working but instead I went back to the bike and removed upper/inlet radiator hose and sure enough coolant flows through at idle at a temp below where its supposed to. I have been in contact with Erik from epic rascing who has been patient and helpful so I will shoot him another e-mail and see what he thinks about sending me a replacement element. Its either that or a missing seal....can't be anything else but I WILL get this right!

  • tech24

Posted January 03, 2011 - 12:23 PM


I got a response from Erik and he's having a hard time believing that the t-stat can be defective but he did tell me it was a stand unit. I'm going to take it apart and hope to see a number stamped on it so I can just pick one up for a few dollars. If not he wants me to send it to him so he can inspect it.

  • grayracer513

Posted January 03, 2011 - 12:48 PM


Are you certain you have it correctly plumbed? By that I mean the main inlet and main and bypass outlets correctly identified?

  • tech24

Posted January 03, 2011 - 01:20 PM


Are you certain you have it correctly plumbed? By that I mean the main inlet and main and bypass outlets correctly identified?

According to the paper that came with it and the pictures on his website it is. The inlet is the silver fitting which is the one right at the head. The outlet is the top red piece. And the bypass is the blue bottom. So as far as I can figure it is. I did send him a pic and he thought is was plumbed incorrectly but I think he looked at the picture too quickly because he mentioned that I had 2 hoses coming out of the head.

  • tech24

Posted January 03, 2011 - 03:25 PM


Okay well I put the thermostat in a pan on the stove, sure enough it opens up at 170 and it was all but fully closed when temp dropped back down to 160. So everything is working the way it is designed. I suppose I'm lost as to why I can't mainting an ECT closer to 170 degrees. Perhaps short plumbing, high flow and the t-stat can't keep up or I just got an issue with some air pockets. Going to bleed it extra long tomorrow and hopefully get it in the dirt and go from there.

  • tech24

Posted January 04, 2011 - 04:52 AM


Got it back together and bled. I still can see flow throught radiator at about 140 degrees but its not coming through the t-stat :excuseme:. I may put some clear hoses on it if I get too concered. I'll post some results when I get it out in the dirt in a week or so. I feel this will work well enough to rid me of excessive fuel delievery. Stay posted!

  • tech24

Posted January 04, 2011 - 04:41 PM


Okay I can't sleep until I figure this out so I went to lowes and got some clear hose. As expected the t-stat appeared to operate properly. I had some flow through t-stat via the bleed hole which is why the hose felt warm all the time. It looks like I confirmed my suspicion that coolant is flowing from bypass into LH then to RH and back to w/p. Its hard to see flow in a fully bled system but I could tell there was some and more than I expected.

Any ideas as what I can do now? I can always block off the LH radiator for winter. Any ideas on a neat and temporary way to do this? I don't think riding around with vise grips on it is a great idea. A check valve would be ideal but not sure one exists for such an application. Any ideas Gray?

I did have one idea that may be a gamble and that is to take an inline 2 stroke t-stat set at 125 degrees and putting it inline with LH radiator outlet. This would act as a check valve sort of. However I have no idea what temp 170 coolant cools down to on the outlet side of the radiator. Is this worth a 100 dollar attempt? Guess I can do so checking with an infrared thermometer. I'd really prefer a check valve if I can find one. Please give any ideas that you may have so I can sleep at night, thanks!

  • tech24

Posted January 04, 2011 - 05:12 PM


I know I'm talking to my self at the moment but I think I may have found the answer.

I'm not sure if I should get the -12AN or -10AN but looking at a conversion chart a -12AN has an ID of 11/16 (.6875"). I assume this would be ideal. Any thoughts?

  • grayracer513

Posted January 04, 2011 - 06:45 PM


I'm thinking don't bother.

  • BlackT5

Posted January 04, 2011 - 07:33 PM


What about this? Its cheaper.


Its what my street bike uses. Its smaller.

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