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911tracker85's Avatar
 
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after market oil line thermostats?

did a bit of searching but no hit on this.

I am in the process of trying to decide if/how to install dual small oil coolers behind the rear fender vents on my 78 930 project SLANT NOSE. have read Porsche put a oil cooler in the rear fender on SN cars but have not found a pic/info on the Porsche solution. but heard if you can find one the price would be outrageous. since 930 conversion no concern about being stock.

the PO who converted this SC to a 930 had run big steel braided lines to the front for an oil cooler. had hit a critter and severely bent the oil cooler. threw all that out.

so could just go traditional with another front valance cooler.

have gotten some concerns about dumping more heat on the rear tires. expect I'll need some debris shield that would divert that air away from the tire. total solution still in the design phase.

the main purpose of this thread is to get more info on the OEM oil line thermostat.

what are the down sides to just eliminating it? I understand it would take longer for the oil to get hot. talking to one guy he commented it has a component for pressure relief in addition to the thermostat controlling flow to a front cooler. but many of the after market ones only control oil flow and do not have any pressure relief.

my plan would just run the oil line from the engine to the driver's side cooler, then in series across to the passenger cooler, and then to the oil tank.

I can see how I could retain the oil thermostat. leave the return line from the engine to the thermostat. and then run lines in series to the rear fender coolers.

would really appreciate any feedback. seems I am thinking of doing something uncommon. and that could mean making a BIG mistake.

someone save me from myself.....

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84 928S, Ruby Red linen/brown interior - preferred DD
87 924S resurrect and gut and another track car...
86 944 turbo my new DE/track car.
78 930 clone project car.

Last edited by 911tracker85; 01-27-2020 at 11:27 AM.. Reason: changing topic
Old 01-24-2020, 07:08 AM
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I dont think things are going to be to happy deleting out the thermostat, its needed much like a thermostat in a watercooled car, to give the water time to cool down in the radiator, same for the oil on start up in a Porsche, the thermostat holds oil between the oil tank and motor, to get it warmed up first then starts letting it flow to a cooler to keep things in check, I think your latter suggestion of integrating in the thermostat to the left and right coolers would make the most sense, much like double oil coolers up front Elephant racing sells, except you have it all in the back. Go check out the flow charts for oil flow Elephant has on their website, if you have not seen, that, may give you some additional ideas for routing the line on the rear, after seeing hwo they do it through the front trunk for dual front coolers. As far as more heat on the rear tire, that would be arguable since the Porsche coolers on the front put all the heat on the right front tire stock, and if you had a left front it'd do the same. I think I'd be more concerned about more heat from the coolers being blown by the fender vents in towards the lower sides of the motor on the lower valve covers/exhaust. But even that probably isnt going to be that significant, the turbo motors seem to run a fair bit warmer from my experience, but I m sure theirs others that could chime in on that with more experience on here. With what you're aiming for I do dual rears with the Thermostat, and get an electric themostat driven fan on each cooler, for warm days, idling through traffic, there are motorcycle fans that are very compact that you could use for that, from Jagg or some of the automotive ones from Setrab. I m sure any additional cooler you add with help.
Old 01-24-2020, 08:24 AM
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My slant came with the rear fender cooler. Somewhere through time something happened to it and they removed it and routed the oil to a front cooler. The rear cooler oil line looped back from the thermostat, that part is pretty easy. The difficult part is all the plumbing to the other side and back, that's a lot of lines in an already hot area. I wouldn't put oil coolers back there, it is an advantage to use the length and free line cooling going to the front then back rather than packing more weight and equipment in the hot engine area.
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Old 01-24-2020, 11:02 AM
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Brian
I respect your opinion and agree with your comments. this idea is not optimal.

do you recall where the factory rear fender cooler was located? I am suspecting the back of the driver's side fender similar to the AC condensers.

if I recall someone commented that a street driven 930 (rarely on boost) does not need more cooling than a street driven 911.

no idea what some future owner may do, but I expect to limit any track time to occasionally a few 20 min DE sessions. and if my build develops near 400 whp I'll be happy.

but no one has answered my question. what is the down side to eliminating the oil line thermostat? other than a slower warm up. but heard from one person a guy blew out a line to the oil cooler w/out the thermostat by reving to high when still cold. I would like to think I can moderate my start-up driving to avoid this.

I can see how to do this keeping the factory thermostat. but by eliminating it the routing of oil lines becomes much less complicated.

cut a little box the size of one of the coolers I saw that I liked. 13 x 5 x 2.5. space behind the vent tunnel is a bit tight. need to look more before abandoning my noodling...

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84 928S, Ruby Red linen/brown interior - preferred DD
87 924S resurrect and gut and another track car...
86 944 turbo my new DE/track car.
78 930 clone project car.
Old 01-25-2020, 07:24 AM
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https://irp-cdn.multiscreensite.com/e112be6e/files/uploaded/thermos%24.pdf
I run the Type 2-16AN HT with a massive Fluidyne oil cooler in the front. I would not suggest running without a thermostat.
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Old 01-25-2020, 02:14 PM
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well folks keep saying dont, but no clear explanation of why not.

been searching / researching and think I am beginning to understand, but would love a knowledgeable explanation.

I am getting the following impression of the operation.

when cold all oil just goes back to the oil tank. nice, short and fairly large lines.

as the oil warms the thermostat starts to open and allow some portion of the oil to flow to the 'cooler' lines. the hotter it gets the more the thermostat opens and the more oil flows to the cooler(s).

I keep finding hints about how the thermostat also provides pressure relief. I suspect two small coolers in series would present such a restriction.

I was looking at info about rebuilding the factory thermostat and see two different parts that should be replaced or proper function verified.

do the aftermarket thermostats also do this like the factory thermostat? read one post that suggests some do not.

so when you hit 7000 rpm the oil pump output flow and pressure may get too high for the restriction in the line to/from the oil cooler. in that case the excess flow/pressure gets diverted back to the oil tank.

is this correct?

ironically I was just replacing the coolant thermostat on a 944 turbo motor I am rebuilding. and started thinking about how that compares to the oil cooler thermostat function.

when cold the water just recirculates, and as it warms and the thermostat opens coolant flows to the radiator. but if the coolant flow exceeds the capacity of the thermostat opening it would just follow the recirculating path.

the more I learn and noodle about this I am now leaning away from rear fender coolers. seems like an interesting idea but flawed for a number of reasons.


so now a shift in my question. how does the external oil thermostat function in conjunction with the one in the case?


now back to researching how to run the oil lines to a large front valance cooler for an slantnose.
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84 928S, Ruby Red linen/brown interior - preferred DD
87 924S resurrect and gut and another track car...
86 944 turbo my new DE/track car.
78 930 clone project car.
Old 01-26-2020, 07:12 AM
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The oil should stay form 180-210F That is the job of the thermostat to keep it in that range as much as possible. The engine thermostat is mainly to control oil flow to get the engine up to temp as fast as it can, once up to temp it basically is wide open. It has to deal not only with oil temps but thermal temps as well. Keeping the oils viscosity as it controls the thickness of the oil film under hydrodynamic lubrication. Oils lose viscosity with increasing temperature.
As temperature increases and viscosity drops the oil film layer gets progressively thinner. Eventually, metal irregularities begin to contact and we no longer have hydrodynamic lubrication. The condition becomes more pronounced as temperature continues to climb and viscosity and film thickness continue to decline. Engine wear increases dramatically. So by removing the external thermostat which its sole purpose is to control oil temperature ONLY, you have an extended oil warmup time frame which is bad for wear. Once up to operating tempurature and during driving conditions without the external thermostate, and using a large oil cooler you will not be able to maintain oil temperature control. With a big oil cooler, and at cruise the oil temperatures can drop dramaticaly below optimum. The external thermostat would maintain the desired oil temp and not drop below.
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Last edited by GJF; 01-27-2020 at 01:40 AM..
Old 01-26-2020, 09:28 AM
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changing the topic slightly.

so I have one suggestion for an after market oil line thermostat.

should I consider getting an after market thermostat? if so why? and which ones are best?

will be going to a large front cooler. run metal/finned lines from Elphant Racing.

my thinking is to rebuild my stock thermostat. but if there are benefits from newer after market ones I would be interested in suggestions.

thanks again.
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Bob Cox
84 928S, Ruby Red linen/brown interior - preferred DD
87 924S resurrect and gut and another track car...
86 944 turbo my new DE/track car.
78 930 clone project car.
Old 01-27-2020, 11:30 AM
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You can use the factory unit. I have been using the Mocal units for many years with great sucess. The biggest plus for me is they come with AN fittings so no adapters required. I typically build lines that bolt to the pan using 4130 Chromoly. I also relocate the oil tank to the front, so it just fit my requirements. Yours may be different.



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Old 01-27-2020, 01:28 PM
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It is never a good idea to remove a thermostat. The result is a totally uncontrolled cooling system. The factory thermostat controls the oil temperature to the engine oil cooler. When you add an auxiliary oil cooler you need to also add an aftermarket inline thermostat to keep these oil temperatures within limits. I added a 44 row Mocal oil cooler to the right front fender for those 100* days running the a/c. I also added a 5" fan controlled by a switch on the dash to be used only if needed. She's been cl ever since.
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Old 01-28-2020, 05:54 AM
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thanks GJF

not taking my car to the level you did.

talked to elephant racing yesterday. they confirmed their metal, finned lines will work with my slantnose. take off from the end of their lines into the frunk and then out to the cooler. rather than run to a fender mounted cooler.

unless someone gives me a good reason, will rebuild my stock thermostat.
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84 928S, Ruby Red linen/brown interior - preferred DD
87 924S resurrect and gut and another track car...
86 944 turbo my new DE/track car.
78 930 clone project car.
Old 01-28-2020, 06:34 AM
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Remember that the factory thermostat also has a low pressure safety valve that returns the oil to the tank/engine rather than through the auxiliary cooling system when the system oil pressure drops below a certain threshold. In a low oil pressure event this may be the last few PSI that saves your entire engine from catastrophe. There are experts that have diagrams that explain how the low pressure diversion valve works and why the a standard MOCAL type thermostat is a poor choice to replace the factory thermostat on the 911/930 cooling systems.
Old 01-29-2020, 02:24 PM
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^^Not correct^^ The factory does have a pressure bypass, but it only functions if there is a restriction in the cooler side. If the cooler gets damaged while the engine is running, it's going to pump out the oil regardless of which external oil thermostat used. The factory oil themostat is a reliable unit designed by BEHR. It is a very high quality unit. But it does not divert oil back to the tank in a low oil pressure senario. Low oil pressure has nothing to do with either thermostat. The only thing one can do is place an IDIOT light somewhere on the dash to warn the driver of loss of oil pressure. MOCAL has been manufacturing oil components since the 60's. They are reliable, but more of a race oriented component. They are easier to package due to their size. They do not have a bypass circuit built into them. Our forum sponsor sells them as well. It is the end users discresion on which themostat to use for what is best for their application. Do a little research first...

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Old 01-29-2020, 05:35 PM
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