Even after engine swap bike is over-heating

Hey y'all...

This is in regards to a '94 VFR750F

So I know i will probably get flamed for this as I hit a nail with a sledgehammer... but my old engine was overheating majorly, and even after a coolant change and "burb" it was still overheating and then started spitting white smoke... figured the motor had gone bad and they are relatively inexpensive so I picked one up off eBay with free shipping for less than $300...did the swap myself and the bloody thing works!

The issue is that it still overheats! Even with the new thermostat, new water pump and new coolant....

Could it be the Cap? The gauge (seems unlikely)? How can I properly diagnose? I do not want to burn out this new motor!

Thanks everyone!

 

I had this same problem with my '82 V45 (the grand daddy of the VFR engines) ... if memory serves, the '94 utilizes a single radiator like the Magna and Sabre?

Check the direction of the radiator fan (also make sure it's turning on).

Many of these were wired wrong throughout the years ... all I had to do was reverse the fan polarity and BAM it was running within the proper temperature ranges.

 

Also, when you swapped the engine, did you swap the rad or have your rad flow tested?

 

Hey Jeff!

Thanks for the response! I did not have it tested and just filled it up with ridiculously expensive Honda Coolant!!

So I just realized that I had to wire the fan directly to a switch because the fan wasn't actually coming on automatically... is it possible that the radiator is bad? Crap...

Will an autoparts store test it out for me? I would hate to buy some specialty tools just to test this thing....

 

Sorry, a bit confused by your answer ... you just discovered now that the fan wasn't coming on automatically? Have you tested it since? Have you tested the direction of the fan? I'm laying bets on this personally - I've seen it with these older Honda V4 radiator fans a LOT where they're wired in reverse or just not coming on.

If you've checked those things, pull the radiator out and take it to a local shop that fixes and repairs rads. They can do a flow test on it to ensure there's no blockages. If someone has not bothered to use distilled water in the past - it could lead to deposits in cooling tubes. It's usually pretty cheap for them to do this test for you.

 

Hey Jeff,

So the fan hadn't been coming on for a while... with the last motor... that may be a tell-tale sign of a bad radiator, right?

Sounds like I may just need to pull this thing and take it to a shop...

Would I be able to save this brand new fancy coolant I just put in it?

 

A bad fan doesn't make a bad radiator - so you fixed the fan and it was still overheating?

Did you check to make sure it was turning in the correct direction? It should be pulling air through the radiator fins. This is imperative - a fan blowing in the wrong direction will actually add more heat to the coolant and cause it to overheat.

There's no real tell-tale sign unless you can see scale build up inside the rad visually where the rad cap screws on ... if you did a complete drain, flush and fill, you can probably save it by pouring it through a strainer into a clean container.

 

Well i'm not too sure if it's turning in the right direction. I will have to check that out tomorrow. Would you be able to tell me what the proper direction is?

I don't see any scales...

I will take my rad cap in to the autoparts store to see if they can test it out... i may just buy a new radiator with cap... i mean... it won't break the bank and will eliminate the radiator from being an issue... hopefully...

 

The fan needs to PULL clean air through the front of the bike and rad, and blow it out towards the back of the bike.

By scale, it could look like anything (blue corrosion, white flakes or sediment, etc). The only true way to tell though, is to simply take it to a rad shop for a flow test.

Testing the rad cap will only tell you if it's leaking and releasing at the right pressure, which doesn't solve your overheating issue.

I really think you need to slow down and stop replacing things instead of just trying to troubleshoot the problem and find the root cause. The overheating on my Honda Magna V45 had me to a point of utter frustration where I too wanted to just replace everything - after many weeks of testing and research - I discovered the fan was turning the wrong direction. It was common that they'd get wired the wrong way and yet there was very little information about it on the web - even the Honda techs at the local Honda dealer I took it too couldn't figure it out that the fan was going in the wrong direction ....

I'm still betting on the fan turning in the wrong direction.

 

Hey all I'm the new owner of an 86 vfr 700 i purchased about a month ago. The bike was almost complete to my knowledge so far besides the fuel pump, but found one at a salvage yard and it works just fine. Problem is, when I went to prime the carbs, the fuel rail began to leak bad. From what I've read so far I'm sure I could pull the carbs and clean them but what about the rails? Seems more disassembly is required to replace the orings? I'm I correct? Any feed back would be greatly appreciated...

 

Welcome aboard! You might want to start a new thread for this so that we're not cluttering the OPs problem solving thread and confusing the different issues you are having.

 

I did that, it was a mistake on my part. Sorry about that guys...

 

Hey Jeff!

SO I have determined the fan is PULLing air through the radiator and not pushing air on to it so it is flowing in the proper direction. I started the motor and let it run for some time with the rad cap off and revved it a few times. On each rev the coolant would go down and then pop back up... some spilled out... but just a tad...

SO i let it idle and watched the gauge slowly go up past half and then stop at about 3/4... it hung there for a while and lots of bubbles were coming out (bike was on the kick stand not the center stand)... i watched a lot of bubbles come out which I believed to be a good sign that the system is being "burped." Then... about 8-9 minutes in i saw the level go down... not a whole lot... but it look like it got sucked in through the thermostat...

keep in mind this whole time the hose on the pump side was relatively cool and the thermostat side was burning hot... (is that normal?)

I revved it a bit more and then the temp gauge made it up the rest of the way so I cut the bike off...

I proceeded to test the gauge by temporarily grounding it and it shot up from C to H so I know it's good...

I attempted to measure the resistance of the sending unit but i wasn't sure what appropriate levels are supposed to be...

If one rail of the radiator is significantly cooler than the other... that could be an issue with that rad itself right? When I squeeze the hoses the fluid moves so it doesn't appear to be blocked...

is there a way to test the water pump to make sure it's engaging appropriately?

THanks so much for all your help!

 

No real way to test the water pump ... has fins and works or it doesn't.

You said you changed the thermostat?

 

wait, wait, wait. You did an engine swap but haven't even serviced the radiator?! freakin' LOL

Take the radiator to a shop and have them power flush and flow test. I had a similar vintage bike that was running hot at free way speeds almost to the point of boiling over. I took the radiator in for a power flush and 60 bucks later in dropped about a 1/4 off the temp gauge. Not perfect but much better.

Depending on coolant used, age, how long stuff has sat etc.. The inside channels of the radiator get plugged with a layer of crust. This prevents flow of coolant and insulates heat transfer. If you can get a hold of a borescope, take a look in the inlet side of the radiator, this is where most of the deposits will be seen. You can also grab an IR thermometer and point at areas of the radiator while the bike is running, you may find drastic temp differences.

as for testing your water pump, you already did that without realizing. The level pull down on each rev was from the pump pick up speed.

 

Yup ... this would be the next thing I'd do.

There's not really anything else left - and really, as Red99RC46 pointed out, probably should have been done when you swapped the motor.

 

Should have been done before he BOUGHT a motor. : P

 

temp switch that controls the fan needs to be ohmed out at 95c temp

 

it grounds fan and turns it on. from your bubbles comment I see that you had air in the system. needs to be bled out for it to work correctly

 

True dat ...

He said he has it switched now ... so temperature shouldn't matter if it's turning it on manually.