An oil temperature puzzle...

[Ken Stapel]

I did try a search, but there are so many threads about oil temperatures, and none of them addressed anything similar to my concern, so I posted a new question. I have a built small block (417ci & around 500hp) in a 1987 Corvette, with an Earl's "Temp-A-Cure™" sandwich-style oil cooler/filter adapter. Why does my oil temperature rise when I am cruising at around 3500-4000 rpm? Around town and in traffic, even on a hot day such as today, the oil temperature runs right around 235-240° with the coolant temperature at around 200-210°. But if I run the engine at higher rpms the temperature starts to rise until I'm looking at 275° or more! The coolant temperature at this point is usually right around 210° which is fine considering. If the oil temp starts getting high, all I have to do is lower the rpm, or slow down, and the temperature returns to normal shortly thereafter. I cruised around today for a while and got it up to normal (240°) operating temperature, and then hosed the cooler down with cool water, and the oil temp started coming down immediately. This indicates that my oil cooler is installed and functioning properly, right? It has been suggested that I add a fan to the front of the cooler, but geez, I have it right out there in front of everything as it is. How much more air could I blow on it? The lines to and from the cooler are wrapped with Earl's Flameguard too. You can see pictures of the installation here. Thanks for any help in diagnosing this one.

 

[sbc350gearhead]

Is that a richmond 5 speed you are running? You may want to back the rear gears down to about a 3.08 if you don't have an overdrive.........that would help with oil temps. Honestly........I would probably run a good 40 weight synthetic and forget about it. Maybe redline 10w40, or RP racing 41. What kind of CR are you running.......what cam specs? [ April 27, 2004, 09:16 PM: Message edited by: sbc350gearhead ]

 

[Michael SR]

ken, can you sense the temp at the cooler somehow to be sure oil is flowing? maybe with an IR heat sensing gun? because those temps sound suspisciously like a high power sbc chevy without oil cooling. something else i thought of, but this only pertains if you kept the stock filter bypass bolted to the block. as the rpm increases, and oil flow increases, the pressure differential across the cooler and filter will become increasingly large. especially the cooler, given its distance and all the hose bends/fittings. so the filter bypass valve will sense this high pressure differential and simply start bypassing the whole filter/cooler loop. so the higher you rev it, the more the percentage of oil flow is bypassing the cooler. then, back at idle, it starts flowing a lot more and cools down quickly. -michael

 

[Michael SR]

fwiw, too, i think your coolant temps are too high. i have a 396 LT4 that's making about 475hp, with a griffin radiator, and no oil cooler. my coolant temps stay between 188-196 no matter the conditions, except stopped in traffic with the a/c on, then it creeps a touch past 200. the oil temps stay in the 200-230 range. the most i've ever seen was about 250 after an extended romp. -michael

 

[Gary Allan]

Are you using #6 or #8 lines there? What kind of pump (HP or HV)?? Oil temps typically climb higher at higher rpm.

 

[Ken Stapel]

I'm glad I checked in here to see if there were any responses. My Internet provider, the almighty Verizon, has done it once again and screwed up my e-mail, so I haven't been receiving mail since yesterday I guess.

quote:

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Originally posted by Michael SR: ... if you kept the stock filter bypass bolted to the block. as the rpm increases, and oil flow increases, the pressure differential across the cooler and filter will become increasingly large. especially the cooler, given its distance and all the hose bends/fittings. so the filter bypass valve will sense this high pressure differential and simply start bypassing the whole filter/cooler loop. so the higher you rev it, the more the percentage of oil flow is bypassing the cooler. then, back at idle, it starts flowing a lot more and cools down quickly.

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Michael, I think this is probably the answer, either that, or I need a larger exchanger. I stopped by Earl's #1 store today and chatted a while with 'em. One thing I don't have with the current set-up is a check valve in the return line from the exchanger. The idea of a check valve is basically to help prevent bursting of the cooler if you have a heavy right foot while the engine oil is still cold. The unit is designed for something like 300 psi or so, but I guess you can still pop it if you're not careful. Anyhow, the check valve will ensure that the oil is not working against itself. Tom at Earl's said also that the exchanger should be attached to the radiator in order to work efficiently, but I have a hard time believing that where I mounted it (see image) is not going to permit enough air to pass over it to cool the oil. Besides, I've got a pusher fan there already; I have no room to mount the exchanger to my radiator. He also said that the oil pan (Canton, 7-quart) is not the best place from which to pull accurate temperatures. I would think it would be the most accurate indication of oil temperature. I'm using a mechanical Autometer oil temp gauge and the pan has a bung to accomodate the temperature sensor. I'm running a CR of 10.2:1 and the lines are -10 fittings. The sandwich adapter is thermostatically controlled as well, but I've wondered about the functionality of the thermostat bypass valve and spring; the thought [u]has[/u] crossed my mind that it may be malfunctioning, eh? Of course, the gauge could be malfunctioning as well I guess. I have run cool water over the exchanger when it was hot (over 200 degrees) and it cooled down almost immediately, but that was at idle and not at four grand. I am running a Richmond 6-speed overdrive transmission. The temps do come down at lower rpms, but the engine doesn't like to live much below 2500 rpm r so.

 

[Michael SR]

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Originally posted by Ken Stapel: I stopped by Earl's #1 store today and chatted a while with 'em. One thing I don't have with the current set-up is a check valve in the return line from the exchanger. The idea of a check valve is basically to help prevent bursting of the cooler if you have a heavy right foot while the engine oil is still cold. The unit is designed for something like 300 psi or so, but I guess you can still pop it if you're not careful.

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i'm not sure i follow. restricting the return line would only add to the pressure inside the cooler. plus, if the thermostat were working, this shouldn't be an issue. i can't speak for any spikes, but i doubt you'd be hitting 300psi even in freezing weather. fwiw, i have plenty of friends running coolers with no check valves.

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Tom at Earl's said also that the exchanger should be attached to the radiator in order to work efficiently, but I have a hard time believing that where I mounted it (see image) is not going to permit enough air to pass over it to cool the oil.

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hmmm... well, it is true that a radiator standing out in the open like that will have less flow through the fins than when encapsulated. i don't know that it would make that much difference, but he might have a small point. i do recall seeing cooler installations similar to yours that worked, however.

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He also said that the oil pan (Canton, 7-quart) is not the best place from which to pull accurate temperatures. I would think it would be the most accurate indication of oil temperature. I'm using a mechanical Autometer oil temp gauge and the pan has a bung to accomodate the temperature sensor.

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this i agree with. the best place to sense oil temps is right where it enters the engine. on my LT4, the oil temp sender sticks partway into the oil passage fed by the filter. when you remove the filter adapter and look straight up into the block, you can see part of the sender sticking in. in the pan, no telling what kind of currents there are, or if the sensor happens to be in a hot or cold pocket, or if it's in a position where airflow is making it artifically low, etc. i didn't realize you're reading temps that high in the pan. wow. maybe the gauge is wrong?

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but I've wondered about the functionality of the thermostat bypass valve and spring; the thought [u]has[/u] crossed my mind that it may be malfunctioning, eh?

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that's a great place to start. while you have it apart, you may also want to install a filter base that doesn't have the bypass in it. just make sure you use a high flow filter, like the K&N 3002. -michael

 

[JHZR2]

my guess is either: -water pump/oil pump flowrate not suficient to maintain 235 steady state temp @ higher rpm -fan clutch cutout at rpm around there -fuel profile leans out slightly at higher rpm, causing higher temps which ae then trnaslated to the oil Just my guesses. JMH