Coolant/oil heat exchangers

On oil to coolant heat exchanger is common on ground based equipment and I think also in marine applications (no experience).

Double check your temperature sensors/ panel read out are working correctly - easy way is to, remove sensor from system, bring water to the boil and place the connected (to aircraft) sensor just a few millimetres above actively boiling surface - instrument should read 100C

Speculation:

In your application it strikes me that the previous owner, fitted this exchanger because he/she was experiencing high engine oil temperatures and this might have been viewed as a quick remedy.

When fitting an oil to coolant heat exchanger, the increased heat load on the Coolant system needs to be taken into account - the fitting of  larger Radiator and or improved air flow through the Radiator should be considered.

In the Rotax powered aircraft context, I would suggest that the fitting of an oil to Coolant heat exchanger comes at significant additional complexity (more potential failure points) and added weight. On the plus side the heat exchanger may take up less under cowl space and aid in maintaining engine temperatures in very cold conditions & in low power descents.

Alternative strategies might include: a lager Oil Cooler (increased cooling capacity) better air flow through the Oil Cooler.

If your coolant has not been replaced in a while, it may be worth while draining your system - flushing it through with clean water - replacing the coolant with a Rotax approved concentrate,  mixed with pure water at 50:50 ratio (I don't trust the pre mixed stuff). Make sure their are no air bubbles/locks in the system and keep a check on coolant levels for the first few hours of flight, top up with mixed coolant, as necessary.

I've never had any luck with the heat exchanger. Seems to always over heat

Cooling can be quite a “science” and sometimes an “obvious” approach to improve the cooling performance does not lead to the desired effect at all.

If the individual cooling system of both oil and coolant work at their limits already a heat exchanger does not really help. If either is somewhat oversized a xchanger helps to distribute/balance cooling capacity to the system with unused cooling capacity.

In case you have the space to increase cooling area or cooling performance (by improving the air flow through the coolers) of oil cooler and/or radiator you should look into that. Personally, I would consider to take out the heat exchanger to get a true/better view on the cooling performance of the individual oil and coolant circuits. Once you have identified the circuit that needs most improvement you can take from there.

It may be a time consuming process to analyze the as-is-performance of the two circuits without the xchanger during long phases of climb and cruise before making changes to the cooling systems but it will, from my own little experience, pay off. The collected data will tell you a lot and help to select the best approach to achieve the desired temp level.

I am curious about the Rans S-19/914.

Wikipedia do not list the 914 as being an engine option for the Rans S-19 - is this a common varient? If it is common then other oner/pilots of this aircraft should be able to give you the benefit of their experience with cooling issues.

With no 914 experience, I would assume that a turbocharged engines would have grater cooling requirements, than a naturally aspirated engine.

If the 914 is not a standard option for this aircraft, it is likely that the cooling system has not been designed for its higher heat load ie this is an experimental aircraft, requiring the owner/pilot to go back to the "drawing board" to design an effective cooling system.

This is some great info folks, I really appreciate all the knowledge and insight. This is my first plane, but I'm having a blast working through its issues. I love flying, but I'm having just as much fun putting my automotive maintenance skills to use!

Sean is correct in that the Rotax 914 is not a standard configuration for the Rans S-19, it was the Rotax 912. In fact, there was an article made about this exact plane! (https://www.kitplanes.com/flight-review-buena-venterra/). From what I can tell, this was likely the first 914 installation in an S-19.

Now that I'm rereading it, I'm running into the same exact cooling problems George was trying to figure out all those years ago. It does looks like the coolant/oil heat exchanger was installed so that the oil carried some of the coolant temperatures though. Looks like redlining coolant temps were a known issue (and still is in hot places despite the adjustments). Worth noting that the plane's had 12 years and 400 hours of flying before I took over.

All in all, it looks like I'll be continuing the cooling R&D! I attached photos from when I helped with the Condition Inspection in April. Figured folks might appreciate some better context regarding layout. Planning on starting out by flushing the coolant and fixing up the radiator to make sure we're working with good numbers (pic shows it could use some love). Then probably looking at improving airflow over the radiator. I've been looking for a reason to put my 3D modeling skills to use and buy a 3D printer to make some molds!

I've found some photos of previous flights and attached data from those incase anyone else stumbles upon this thread! Maybe in the future, I'll get an engine monitor that will allow me to export data out.

Temperature Numbers

Flight 1

Status: Cruise

Altitude: 8,900ft

MP: 29 inHG

Prop: 5000

OAT: 32F

Oil Temp: 177F

CHT: 216F

Coolant: 195F

Flight 2

Status: Finished climb out (same trip, next leg)

Altitude: 9,700ft

MP: 28.8 inHG

Prop: 5000

OAT: Unknown (in AZ November, ~60F likely on ground)

Oil Temp: 211F

CHT: 245F

Coolant: 226F

Flight 3

Status: Cruise

Altitude: 8,900ft

MP: 28.1 inHG

Prop: 5000

OAT: Unknown (Phoenix area, November, likely ~35F at altitude)

Oil Temp: 175F

CHT: 219F

Coolant: 200F

Flight 4

Status: Cruise

Altitude: 9,700ft

MP: 29 inHG

Prop: 4900

OAT: 32F

Oil Temp: 181F

CHT: 215F

Coolant: Not displayed (argh)

Flight 5 (our current data!)

Status: Top of cruise climb (was testing 5,000-16,000ft performance via 1,000ft increments every few minutes)

Altitude: 6,500ft

MP: 31 inHG

Prop: 5000

OAT: 66F

Oil Temp: 218F

CHT: 246F

Coolant: 234F