Overheating on 914-6 w/ 3.6

Porsche84 · Porsche84's Garage

Hi Guys

I'm chasing an overheating problem in a 914-6 with a 964 engine. We've added two coolers up front, removed thermostat, tried with/without engine tins , added a fan on front cooler and still can not prevent overheating. The car is a track car and runs up to 240-250 fairly quickly on moderately warm days. I even swapped the computer in case it was a timing issue. I am wondering if it might be the 914-6 oil tank. That is about the only difference from other 911 3.6 conversions I've done. Any thoughts? Thanks

John Rogers · 09-12-2012, 07:26 AM

Several things to check I'd say. First, what sort of ducting is there at the front coolers and how large is the outlet after the air gets heated? The air flow has to be large and channeled so that the cooler is the only thing getting any air. Second, are the front coolers actually letting oil flow through and is any heat being removed? This is a bit harder to check and a diagram of the system would need to be evaluated as well as temp measurements taken with a pyrometer so that flow can be checked. Next to check is the size of the front cooler lines, are they at least -12 and have no blockage due to sharp bends that may have collapsed the inner tube walls?

You will need the engine tin and the seal to keep that exhaust heat under the car. The thermostat is not needed although many say it is. We also made sure to have a "GT" style of engine lid and raised the rear of the Targa top about 1.5 inches so air would flow in and break the vacuum over top the engine lid since that is a huge low pressure area.

On my 914-6 2.8L race car we had -12 Earls's SS lines and the largest cooler we could cram in the front, width wise. I made the ducting out of aluminum sheet and the outlet went through the huge hole in the front trunk. We also insulated all the lines with either fire sleeve or heat wrap and that helped slow things down, especially when the oil lines were near the engine.

When all was hooked up, a test was done to measure oil flow from the cooler by pulling the coil wire and cranking the engine to see how well the oil pump would push the oil through. It acted as a final flush and a measure of how well the system flowed and ended up sacrificing little oil as it went back to the oil tank.

pcar916 · 09-12-2012, 11:44 AM

John's remarks confirmed...

I'm running the stock 914-6 oil tank as well and my 993 engine doesn't have the Behr engine cooler you do. I never suspected the oil tank so have no input on that one.

It too ran hot in the summertime and on the track so I did two things. The first was to delete the downdraft exhaust in the front trunk and route the cooler to exhaust out the hood (no fans). That helped a lot. But it still ran too hot in my opinion.

This next paragraph is irrelevant to you because you still have the Behr... probably, but I'll add it for any other potential 993 converts.

I added a 20.5K BTU cooler via a sandwich adapter (high-pressure circuit) on the engine filter console to replace the Behr. Now it runs cool but the sandwich adapter makes for a somewhat higher oil pressure reading. I know it's the adapter since, when I remove the cooler from the circuit the pressures remain the same.

Note: My return hose is -16 from the tank, and the remainder of the system is -12. If I were doing it today I'd go -20 / -16, especially since my front cooler is already plumbed with -16 fittings.

Good Luck

John Rogers · 09-12-2012, 06:50 PM

In the cooler outlets that I have seen from the top of the front hood, there is always a Gurney flap at the front so there will be some low pressure created behind it and help suck the hot air out. Most of the racers I vintage raced with used the bottom outlet as the pressure under the car was lower and gave much better air flow out.

One thing about the bottom outlet is watching those off pavement side trips. Many years ago at a spring vintage race at Willow Springs a 911 went off and then back on and then into the pits to be checked out. The officials had the driver kill the engine as they heard some sort of high pitch screaming noise and in a minute a ground squirrel can flying out from under the front of the car. Seems the driver had scooped up a rider!!!!

pcar916 · 12:45 PM

S'true about the flap. This particular certainly outlet worked better with it. When I had mine exiting out the floor I had one on there as well, but it kept getting smashed flat... never had any animal interaction that I knew about.

I made 3 of them with different heights (they're interchangeable) and the ~2 in version worked best overall. As always, the closer to the front bumper the outlet is the lower the pressure. My first sketch had the outlet much longer and going back halfway to the windshield. Never built that one once I did the research on the pressure.

Note: You'll get more water on the center of the windshield in the rain, but it's never been a deal breaker.

I can't prove it, but I decided to put the inlet in the front bumper to take in air a bit farther front the hot pavement.

Since this is reaching toward OT I'll stop with this (almost) highjack.

Porsche84 · Porsche84's Garage

Thanks for all the comments. The 964 engine does not have the Behr cooler and does not have the 993 second oil filter. The oil lines in the car are all -12 so I'm thinking the lines need to be -16. The radiators are ducted to the bottom of the car with a fan, but maybe the top would be better

pcar916 · 09-13-2012, 11:25 AM

Makes sense. The 993 needs the extra oil filter for the hydraulic valve components. Lots of folks use the underneath approach successfully so maybe they'll chime in but I like mine. Three things to think about.

1. Tougher fabrication... not bad, just more effort
2. SCCA won't like it so check the rules in your class and make sure you can do it at all if you're thinking about running any of their events.
3. Water is a bit harder to keep out of the front trunk if that matters.

Since mine's a street car still I block off a little portion of the front cooler and run it (via a 4 in bilge-fan) into the stock heater ducts. It's my heat in the winter and defrost in the early spring and late fall. Without the onboard oil coolers the 993 (and now I know the 964) engine oil gets hot faster than the earlier engines.

good luck