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Some older posts have sort of hit around this issue, but maybe not emphasized it.
I had presumed that with the stock or aftermarket dual oil cooler systems with thermostats, that in winter the warned up engine oil temperature would be safe and in the ball park. But this is incorrect. A few years ago, a friend upgraded his single unit to a large serial dual oil coolant system. In summer all was fine. In winter his water temps were very slow to reach normal. A new water thermostat did not solve the problem.
I gave him a few thermo sensing strips to place on parts of his engine. It showed that his oil temperatures were very low. Even though oil was bypassing the second cooler, its mass was absorbing a lot of heat from the oil passage.
I then checked my R1 stock system, and I had the same problem.
We both tried blocking our second oil coolers by stuffing a large rag into the inlet duct. This solved his problem and also increased my oil temps to normal.
Each winter we now do this to keep the oil temperature warmer.
Do not know if this is needed for track events or not.
Another thing it helps with, stops or reduced the oil foam in the filer neck as the hotter oil temperature helps evaporate blow by moisture.
Good info, I block off 50 to 75% of my dual oil cooler surface area with cardboard and zip ties once the temp drops below 32*.
"Bob is the oil guy" is a great place to find a lot of oil related information, it will help you make better decisions about oil related issues like the OP mentioned.
I recently switched from dual FD oil coolers to a single large oil cooler in my FC, and since the single oil cooler does not have a internal thermostat like the FD oil coolers, I installed a 180f degrees mocal remote thermostat.
I too noticed that the oil temps do not get above 150f during these cold days. I thought I was having thermostat issues, but if you experience the same problem with stock FD oil coolers...
It's easier to block off the coolers than to fit an aftermarket thermostat. One less thing to worry about.
It's one less thing to worry about, worrying about whether or not the coolers need to blocked that day? Versus a thermostat that just works?
Perhaps it's time to install a series of switches on the dash, one to each injector, so you can manually pulse them with 12V to control AFRs. Because an ECU is one more thing to worry about.
I think the issue as touched on upthread is that the thermostat is in the oil cooler itself. Meaning the oil cooler acts as a large heatsink that can effectively cool the oil even though the oil isn't actually passing through to any large degree, just going through the bypass. With a 120 degree temperature delta, you don't need much cooling capacity
So a close-in mounted thermostat would be better so the oil never goes near the big fat heatsink up front. Although, I have never actually had the oil thermostat out of any RX-7 oil cooler, so I couldn't say if there's a deliberate bleed to keep temperatures relatively stable. Wouldn't want to shock the engine by hitting it with ice-cold oil.
I think the issue as touched on upthread is that the thermostat is in the oil cooler itself. Meaning the oil cooler acts as a large heatsink that can effectively cool the oil even though the oil isn't actually passing through to any large degree, just going through the bypass. With a 120 degree temperature delta, you don't need much cooling capacity
So a close-in mounted thermostat would be better so the oil never goes near the big fat heatsink up front. Although, I have never actually had the oil thermostat out of any RX-7 oil cooler, so I couldn't say if there's a deliberate bleed to keep temperatures relatively stable. Wouldn't want to shock the engine by hitting it with ice-cold oil.
Cardboard is cheaper though.
My understanding is that the remote mocal oil thermostat is a bypass unit. If that's the case, the one that I have is opening before 180f.
I'm have an after market three row cooler without an internal thermostat so I'm using an Earl's thermostat. This bypasses the cooler completely until the oil is up to temp. It also has provision to monitor oil temp/pressure before and after the cooler.
Last edited by KansasCityREPU; 01-31-16 at 03:52 PM.
It's one less thing to worry about, worrying about whether or not the coolers need to blocked that day? Versus a thermostat that just works?
Perhaps it's time to install a series of switches on the dash, one to each injector, so you can manually pulse them with 12V to control AFRs. Because an ECU is one more thing to worry about.
The stock R1 systems and many dual systems do have a thermostat.
But they are set up to prevent overheating of the oil, not being too cold.
Exactly the opposite actually.
The thermostat is there to ensure proper operating temp (keep the oil from being too cold). A thermostat will NEVER increase the heat rejection capacity...
The stock oil coolers all have internal thermostats. Which bypass the heat exchanger core to a varying degree based on the oil temp.
Technically they are not called thermostats, as a thermostat is a sensor only device....
The technical term for them (including coolant thermostats) is "Thermostatic Bypass Valve"
Thermostatic valves work progressively with temperature so it's not an "Open or shut" case
If the stock system is not maintaining proper temp then the TBV has failed and a new oil cooler is needed.
bypass oil thermostats like the mocal unit do not prevent flow in and out of the heat exchanger cores but prevent bypass flow based on temp.
The heat exchanger ports are always open to flow, but the bypass is open when cold, closed when hot. Cold oil bypasses the exchangers by taking the path of less resistance through the open bypass valve but there will still be some oil flow through the heat exchangers when cold.
Once hot, the bypass closes and all flow is directed through the heat exchangers and nothing gets bypassed. Since this is actuated via an expanding wax, the rate of bypass is continually variable until full hot.
Last edited by neit_jnf; 02-02-16 at 11:19 AM.
Reason: added awesome PaintCad dwg :D
my point is that in cold weather with the bypass open it is still possible to have enough flow through the coolers to prevent operating temp to be reached
I've not used that specific model but all the stock oil coolers ive used or delt with including dual FD oil coolers and two FC oil coolers in parallel arrangement come up to full operating temp relatively quickly even in sub zero temps.
If they don't then i suspect the bypass is stuck closed and thus the thermostatic element/valve needs replacement.
bypass oil thermostats like the mocal unit do not prevent flow in and out of the heat exchanger cores but prevent bypass flow based on temp.
The heat exchanger ports are always open to flow, but the bypass is open when cold, closed when hot. Cold oil bypasses the exchangers by taking the path of less resistance through the open bypass valve but there will still be some oil flow through the heat exchangers when cold.
Once hot, the bypass closes and all flow is directed through the heat exchangers and nothing gets bypassed. Since this is actuated via an expanding wax, the rate of bypass is continually variable until full hot.
Originally Posted by neit_jnf
my point is that in cold weather with the bypass open it is still possible to have enough flow through the coolers to prevent operating temp to be reached
You don't need a thermostat if you don't mind tossing in a piece of cardboard.
I tossed around the idea of a bypass T-stat for dual 30 row setup on 20b, and said the hell with it. Too many extra fittings that can leak for a car that isn't a daily driver. All you have to do is watch your oil temp and make sure the car is nice as warm before you beat it up. A piece of cardboard did me fine, over the first cooler in the series! Never saw oil temps under 170F, they only dropped when hitting the interstate. And changing the oil every 1500 miles or less, from gas-dilution, ensures that you don't have too much moisture build-up from running too cold.
I live in Alabama though, weather never drops below 25F or so.
Another thing I do since my car is garaged: Upon garaging the car I pull out the oil dipstick about 2 inches and remove the oil filler cap. I leave it this way for a couple of hours. This helps to ventilate the oil pan to remove some moisture and gas fumes. You go back into the garage after a few minutes and you can smell that it is working. Keep the garage door open a couple of inches while doing this.
Another thing I do since my car is garaged: Upon garaging the car I pull out the oil dipstick about 2 inches and remove the oil filler cap. I leave it this way for a couple of hours. This helps to ventilate the oil pan to remove some moisture and gas fumes. You go back into the garage after a few minutes and you can smell that it is working. Keep the garage door open a couple of inches while doing this.
You are wasting your time doing that. Any fumes will escape out of the PCV system. If you have gas in your oil that needs to "evaporate off" you have a series of other problems.
I have a Mocal thermostat and Setrab cooler on my V8 and the Mocal works as shown in the picture.. There is always some oil circulating through the cooler. If you get on the freeway and/or drive in cold weather, your oil may not get up to temp.
The Mocal is set up to do this so if it fails it is never an oil restriction.
The oil additives do a remarkably good job of retaining it until the oil is changed. The most a PCV system can do is grab it before the oil has a chance to do it.
Another thing I do since my car is garaged: Upon garaging the car I pull out the oil dipstick about 2 inches and remove the oil filler cap. I leave it this way for a couple of hours. This helps to ventilate the oil pan to remove some moisture and gas fumes. You go back into the garage after a few minutes and you can smell that it is working. Keep the garage door open a couple of inches while doing this.
That's weird.
You are likely smelling the fuel tank, which vents into the PCV system.
Just a nitpick on your sig, but his name is not "Dr. Who", his name is "The Doctor".
You are wasting your time doing that. Any fumes will escape out of the PCV system. If you have gas in your oil that needs to "evaporate off" you have a series of other problems.
Many modded engines such as mine have removed that systems as it sucks dirty oil into the turbo, IC ,and intake system.
I use a catch can.
And for stock seq engines, it pollutes and makes it harder to pass emissions testing.
The oil additives do a remarkably good job of retaining it until the oil is changed. The most a PCV system can do is grab it before the oil has a chance to do it.
Sorry dude you are so wrong about gas in hot oil! My PCV system is removed. I use a catch can.
01-28-16, 01:04 PM
