CHT vs Oil Temp

1432 · Posted: Fri Jun 13, 2008 9:09 pm Post subject:

Jimmy
Quote "Your coolant temp is the minimum temp of your motor. Everything else is warmer. That is the purpose of the coolant. To cool the motor. If you dont have any exterior oil cooler, How could you expect your oil to be cooler than the motor itself?? Just does not make much sense"

stands to reason for oil to be at a slightly lower temp since water cooled thru the radiator enters the block first then passes through the heads.

Jimmy111 · Posted: Fri Jun 13, 2008 6:51 pm Post subject:

dog_jr911 · Posted: Fri Jun 13, 2008 6:04 pm Post subject:

wait.... was the 0w-60 oil a joke? theres been alot of talk about using the 30mm oil pump and having to use thinner oil. right now, im using the same stuff there putting on the new vettes. 10w-something....

i read car and driver the other day, and the new nissan GTR uses 0w-60 oil.
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nikita · Posted: Fri Jun 13, 2008 8:48 am Post subject:

1432 · Posted: Fri Jun 13, 2008 7:31 am Post subject:

Jimmy111, Art,
for decades myself and many of my group have run 2.3 - 2 .7 ltr type 1 & 4 engines for in our sand cars on methanol with no tin or oil coolers
whatsoever, ambient desert temps were 80 - 100*. Actual head temps (not at plug) rarely exceeded 230* oil temps were never higher than head temps. these engines were purposely tuned on the rich side as a lean condition would cause elevated temps in both areas. While these engines were never used at 100% duty cycle they were used in much the same manner as their gasoline, oil cooled fan shrouded counterparts. This, to me shows a direct relationship between head/cyl and oil temp, your thoughts?

Art Thraen · Posted: Thu Jun 12, 2008 9:19 pm Post subject:

(Jimmy111) I have 1915's and 2332's on mining equipment that is completly unshrouded. They run at about 400 CHT and they are jetted a little rich but I have little problems with them. I just use 72 plate oil coolers with fans and have little problems.

.[/quote]
I would like to see PICs of this! Really! I love to see cool stuff.
Art @ ACE

Jimmy111 · Posted: Thu Jun 12, 2008 9:46 am Post subject:

AS41 has a maximum temperature rating of 300F But as you aproach this Creep accelerates. It is the main reason that the center journals get out of round in Type 1 type cases. It only takes one overheat to do this. It bacame a big problem when VW had to meet emissions and raise the exhaust gas and oil temps. That was the reason for the change to AS-21

The oil journal to water jacket is for water cooled motors . Not ACVW
Your gage was incorrect in your BMW or you had other problems. coolant temp should always be higer than boiling on all emission controlled cars. Oil temps in Water cooled motors are never lower than the coolant temp after the motor gets warmed up. There is usually about a 10 degree differance.

nikita · Posted: Thu Jun 12, 2008 9:30 am Post subject:

Jimmy111 · Posted: Thu Jun 12, 2008 7:53 am Post subject:

1432 · Posted: Thu Jun 12, 2008 7:16 am Post subject:

Jake,
I guess you just don't see the basic relationship I'm pointing out. the one that's been relied on for over 100years by the automobile manufacturers

Jake Raby · Posted: Thu Jun 12, 2008 6:52 am Post subject:

1432 · Posted: Thu Jun 12, 2008 6:46 am Post subject:

If cylinder head / cylinder wall temps have no little or no relationship to oil temps, think about why our basic water cooled cars need no added oil cooler to maintain oil temps no higher and usually lower than their corresponding water based coolants.

Jake Raby · Posted: Wed Jun 11, 2008 7:27 pm Post subject:

Eaallred · Posted: Wed Jun 11, 2008 3:53 pm Post subject:

Here's my take on it from what i've experienced.

Head temps are related to engine load. That's about it.

Oil temps are slightly effected by head temps, but the majority seems to be effected by engine rpms. Heavy valvetrain/springs seems to increase this heat over light stock components. My theory there is the flat tappet cam and lifter setup has the oil taking a lot of the friction/heat abuse. The more load on this (via lifter to cam pressure, and an increase in rpms) the higher the oil temps get.

Oh yea, John, the 'magic' number was about 53mph. As long as I kept it under that speed, the oil temps stayed under 220 in that 90 degree weather.

One more bit of useless blabbering from me. My drag motor running E85 runs cool as a cucumber on the cylinder heads. But just idling (to get the head temps up before I run) with those K-800 springs and big heavy stainless valves, my oil temp will get right up close to 200 degrees even before I make a pass down the track. When I ran gasoline, the heads warmed up so fast oil temp was never an issue, lol.
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Jimmy111 · Posted: Wed Jun 11, 2008 12:00 pm Post subject:

There are big hills around where I live. But I havent ever seen temps over 400.. The cylinders and heads are cooled mainly by the exhaust and incoming F/A mix. The blower is there mainly to provide circulation because it is in an enclosed space. The fan requires a lot of HP to overcone the pressure differances between the incomming negitive air pressure and the presurized area under the car. The freer flowing the exhaust and the higher the vaccum, the more cooling of the heads and cylinders that takes place.

I have 1915's and 2332's on mining equipment that is completly unshrouded. They run at about 400 CHT and they are jetted a little rich but I have little problems with them. I just use 72 plate oil coolers with fans and have little problems.

I always thought that VW should have designed a draw thru cooling system that would pull the air from Below the car and exhaust it out the back. Take advantage of the 2 psi or so under the car and reduce the energy load on the motor.

I know that busses are much more prone to overheating the heads. I had 2 busses and never had CHT guages so I couldnt tell you the temps... But I never fried the heads either.

Just my experiences and views. I really need to look into the overheating problems with busses.

John. I have a good study on bearing oil clearances and heat generation if you are interested in it. It is not VW but it is good.

[email protected] · Posted: Wed Jun 11, 2008 11:24 am Post subject:

I could be wrong but I think I heard that the Berg's cam break in machine gets oil temps around 170F, and that is with NO COMBUSTION, just the valvetrain!

John
Aircooled.Net Inc.
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nikita · Posted: Wed Jun 11, 2008 11:13 am Post subject:

John, There you go again trying to inject facts and logic into a discussion.

Here is my take on this. CHT can change in seconds, where oil temps take several minutes to move significantly. Oil temp and pressure relates primarily to the bottom-end health of your engine where parts are pressure lubed, CHT and EGT the top end where combustion takes place. Ive repaired/replaced many valves and heads and never had to replace a crank in stock engines.

[email protected] · Posted: Wed Jun 11, 2008 10:49 am Post subject:

Head frying can happen climbing the "hills" we have around here. The oil temp will be fine but CHT thru the roof.

I suspect he didn't have a CHT gauge. We've all been there, usually some blow up leads to an increase in our knowledge.

I consider oil temp to be proportional to RPM, CHT to load. You can free rev a motor on a stand with no load and overheat the oil if you want to prove this to yourself. Especially with thick ass oil and oversized pumps. Most people just stare at me when I tell them their oil temps would drop if they'd use a thinner oil. OK, don't believe me? Use some Valvoline 60W and really cool it off. Rolling Eyes

John
Aircooled.Net Inc.
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Jimmy111 · Posted: Wed Jun 11, 2008 9:47 am Post subject:

The cylinder head temp is mainly a factor of fuel load and mixture. The oil temp is a mainly a factor of bearing pressure and cylinder head temp. Cylinder temp contributes to this by the oil flow thru the head. On tests I did, the oilflow was much more important than the airllow when the motor was removed from the car. Many people who have had flaps and a thermostat in their shroud have seen that when the thermostat fails closed the car can still be driven around untill the oil gets too hot. This is a factor of the oil cooling the head.
The oil gains most of its heat thru the compression of the oil film thru the bearings. This heat rise of the oil can be as much as 80 degrees on a 1600 at a 45hp load at 3800 RPM.

Both are important. They just have different causes.

I dont know why eric fried his heads. Possibly the altitude change?

[email protected] · Posted: Wed Jun 11, 2008 8:38 am Post subject:

FWIW, several years ago when Eric Allred was McGyvering on his Bus, he drove around for a while with NO OIL COOLER AT ALL (not even the stock one in the shroud). And it did not run hot oil temps unless he was over 50mph or so. Crazy.

He knows a lot about oil, oil temps, and cooling, so listen to him.

John
Aircooled.Net Inc.
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