BF 225 Cooling Mystery

Remove t stat and put it in pot or hot water see if open all the way or close all the way sounds stuck open What is thermostat rated for?? Switch the two see if problem moves jus a thought and few optionsAnd no 20degree difference should not affect engine long term unless its 20degrees hotter than rated cooler no bad

T-stats rated for 160 F. Already did that test on both old and new t-stats. Plus, the fact that both t-stats go to 160 F after engine is shut off, but key stays on, indicates that it is a water circulation issue. Currently, the engine is at the dealers for a 400 hour maintenance. I asked them to do a thorough back flush. But I doubt that will change anything.

When I get the engine back, I will test the t-stats again, then I will run it up with the cover off and testing with a heat sensor gun to confirm the gauges. But the bottom line appears to be that the right side of the engine is cooling more than the left side dispite the t-stat rating.

Hi CHawk_man,

It has been my experience that what's happening on the OUTSIDE of a given system is not always a good indicator of what's taking place on the inside. Sometimes you get useful info taking metal surface temps and sometimes not so much.

I used to be a mechanics trainer for San Diego Transit Corporation and they were having some serious cooling system problems a few years back. In the course of teaching the techs how to troubleshoot the cooling systems on their buses, we tried numerous methods for taking temperatures of thermostat opening/closing events and radiator and oil cooler heat exchange rates. We found that the most accurate method for determining what was occurring in the coolant stream was to insert bead thermocouples directly into the water jackets via convenient entry points like slipping a bead between a pipe and a radiator hose or through access points we fabricated in the housings for the purpose of testing.

I was pretty disappointed at how inaccurate the infrared heat guns were for doing these tests because they are WAY easier than going through that other drill. But, we found that the data just wasn't all that reliable with no contact and direct contact to the outside surfaces of the cooling system. Differences in metals and thicknesses of components at various places made determining heat transfer from the coolant to the surface pretty unpredictable.

If there are even small differences in the physical make up of the manifolds on your engine then I would expect that there could be big differences in heat transfer rates to the surface of one as opposed to the other. If they are fairly identical then maybe not.

It sure does sound as if you have one side opening and then modulating as it should and the other just opening and hanging open. Or, at the least, opening and then modulating at a lower than desired temperature. That would HAVE to be a function of the thermostat itself.

Would you consider swapping the two sides to see if the condition follows the stat?

I don't like the fact that one bank isn't heating as it should and it would, probably in a very small way, effect performance. But, I wouldn't think it would be all that detrimental to the engine.

At any rate, this is an interesting puzzle and I'll be watching for anything that you may uncover.

Jimmy - Good insights. Thanks. As soon as I get the engine back, I will re-establish a baseline on the temperature differences, then start doing some other tests - swapping t-stats, heat gun sensor while underway, and so on. I just want to get to the botom of it. My suspician is that there is a design issue, but it is not obvious from the diagrams in the shop manual. I need to pretty much eliminate every other possible explanation before I can support that conclusion. I'll keep folks posted on my progress.

BTW - I guess what started this hunt was that I know that if the engine is not running at the spec temperature, then it is not likely running efficiently, and I really try to keep it as efficient as possible. I burn about 100 gallons of fuel every two to three weeks, and that is getting really pricey.