Checklist for reducing heat in hot-running engine.
 

Can we stand another "my engine is running too hot" thread?

You guys scared me with posts about running an SC with the temp needle sitting at the 9 0'clock position. This appears to be equiv. to about 220degreesF. Without direct temp. numbers on my SC's "white-none-red" gauge I had always figured I was OK at mid-point.

So, what can be done to reduce the engine heat? Being an SC, I *believe* I have the better fan ratio (tell me if I'm wrong) I thought I would attempt to start a list of fixes. Tell me/add your thoughts if you would.

Cheap:
= Remove all dirt etc. from trombone, lines, and oil tank.
= Check for foreign matter in engine finning, etc. (Can you safely jet-spray from the bottom of the engine at a car wash?)
= Check CO2 (I run at 3.5% per JohnW's advice)
= Check timing
= Remove side rocker to expose/cool lines

Less Cheap:
= Swap the dino oil for synthetic (do you flush system by running synth for 50 miles then dumping it, plus old dino.?)
= Upgrade to Carrera/Mocal with fan
= Alter air access in some way to direct air to trombone cooler. How to do this?
= Swap in thermostat that opens sooner? Available?

Many thanks for your thoughts. At the mid-80's in temp., I can get my oil temp. needle just a tad north of horizontal.

John

John, Those are mostly good thoughts.

I wouldn't bother removing the rocker cover. It is open enough that plenty of air flows though it.

If you change to synthetic oil, a 50 mile flush isn't necessary.

Trombone won't respond well to inceased airflow. The Carrera cooler will.

You wouldn't want a lower temp thermostat. The tstat is fully open by 210. Above that temp your cooling system is maxed out and not regulated by the tstat. Having that tstat open lower wouldn't help.

For even more cooling capacity you could add a center mount oil cooler and or finned oil lines.

Before doing anything have you verified that your gauge & sender are accurate? It may be a non-issue.

This is a great checklist. Grady's suggestion about fan ratio is one to add to the checklist. Also, for cars older than 1977 (?), I think the air deflectors will need to be modified to the later design (remove some metal) to get better airflow.

One of the more recent Panorama issues had a pretty good article on cooling 911's. It mentioned something about how the numbers are still on the temp gauge but that you have to look at it at an angle to see the numbers. This was news to me.

-Don B

In the heating industry, they use something call fin tubes for baseboard radiant heaters. It's a small aluminum fin that wraps around the copper tube to help radiate the heat. I always wondered if adding fins to the trombone heater would be a cheap alternative for helping the efficiency of the trombone cooler.

Mid point on my 77 911S gauge (marked in celcius) is exactly 100C, or 212F.

-MAS

Switching to synthetic won't lower temps in itself. It will however, give your engine added protection at high temps.

My best "upgrade" oil cooling was blocking off the air spilling under the cooler and forcing it through the cooler. I also pulled my front fog.

I too was having concerns about my oil temperature due to these hot Alabama summers. After examining my oil lines I felt that there was just too many 'mashed' areas through none were flattened more than 50%. This provided a good opportunity to perform two projects that I have been wanting to do: install Elephant Racing's finned oil lines and install a 28-tube cooler. My choosing this type cooler over the other coolers was based on the repeated recommendation in Bruce Anderson's book which made very good logical sense. I realized 10° F reduction in temperature just by the addition of the finned oil lines and and overall reduction of 25° F by the addition of both the finned oil lines and the 28-tube cooler. I am maintaining about 185° F when the outside temp is 90° F which I think is quite a success.

If you are in the market for this type cooler, there currently is one on Ebay (no affiliation I just look since these are tough to find coolers):
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7914949999&catego ry=46095

Contrary to the adage “Never say never.” I’ll go out on a limb and contend that no 911SC had both 1.81:1 fan ratio and the 245 mm 11-blade fan simultaneously.

The ’78 & ’79 911SC had 1.81:1 ratio but the 226 mm 11-blade fan. The ’80 and later had the 245 mm fan but the pulley ratio reduced to 1.68:1.

Please correct me if I’m mistaken.


Regardless, the combination of 1.81:1 ratio and the 245 mm 11-blade fan is probably the best you can get with stock 911 parts.

There has been some discussion of a fan pulley size of 80 mm as opposed to the published 84 mm fan pulley diameter. Who can shed some light on that? What years, models, part numbers? If there are standard Porsche parts available with an even smaller fan pulley the overall ratio might be 1.9:1.

On one of the former threads we discussed custom crank pulley larger diameters and modifying the engine mount to fit.


I will reiterate what I have said several times. The best way to address high temperatures in an air cooled 911 is to pump more mass air flow across the head and cylinder cooling fins.

With the “mild cam” engines (T & CIS) we are tempted to drive in the 2-3000 RPM range. With high temperatures, you should buzz along at 4-5000+ instead. It is RPM that pumps the air. There is the added benefit that the A/C condenser dissipates more heat with higher air flow (fan ratio & RPM.)

Jim is possibly correct about the cylinder baffles. One consideration about this heat exchanger (HE = cylinder and head fins) is that there is greater heat transfer from the HE to the air with greater pressure drop across the HE. The other side of the equation is that with greater pressure drop there is less mass air flow. Every HE has an ideal pressure drop–to-air flow ratio. That is why some with small cross section area and very thick are designed for high pressure drop and others with large cross section area and thin (like most automotive radiators) are designed for large air flow and minimal pressure drop. I don’t know what that ratio is for a 911 but I’ll bet it’s not far from stock.

Years ago, I considered “cross drilling” 911 head and cylinder fins and press-fitting tubes or rods of copper/brass/aluminum in order to increase the total surface area of the HE. I settled in on the fan ratio and the “Rubbermaid Solution” as the most effective and least cost.

Best,
Grady

haha I love how chuck is always willing to give advice but never touts his products...so I will

go to ELEPHANT RACING

finned oil lines, carrera coolers with larger ports...

I should add to the list that using a bra on the car will prevent air from going through the slit between the valance and bumper.

Since my car came without foglights ('78 SC Targa) I may put some louvres vents into the passenger side. On the reverse side, a bit of ducting to direct the air to the trombone.

This short of going to a Carrera/Mocal. We just rarely see the hot weather up here so this is a concern only about five or so days of the year. Otherwise the temps are perfect for the Porsche engine.

John

Slight change in topic -- what do people think of the Earl's coolers?

Is it worth taking the one off my car that the PO put on and going with a Carrera cooler?

I believe Grady clay is correct as to the offered pulley sizes and fan sizes. I don't think there is a combo of 245 mm and 1.8:1

I've found that 1.67:1 ...and 1.8:1 is really not that different, and is more influenced by the number of pulley shims you use between the pulley halves to get the belt tight. Prety close.

Yeah...Porsche used 80, 83 and 95 mm fan pulleys. Why they even bothered between 80 and 83 is beyond me. Just causes problems.

---Wil

I agree with Wil, the ratio is influenced by the variable (uncertain?) diameter of the fan pulley. What I have been quoting is the Factory specified numbers that Porsche actually published. If you just use the various diameters, you get all sorts of peculiar ratios.

I would be interested to see if someone has put counters on the fan and crank pulley and determined the actual ratios with various components.

Wil, could the difference between 80 mm and 84 mm on the fan pulley be just the difference between a measured dimension and the Porsche specified number? If there is a part with smaller-than-84 mm diameter, that would be great.

An interesting exercise might be to make several slightly different 134+ mm diameter crank pulleys and run the fan pulley with all six shims (7+?) between the pulley halves to minimize the fan pulley diameter. The limiting factor is the inside of the fan belt can’t touch the pulley shims. You can make a single shim of proper dimension so you don’t have to deal with PIA multi-shims getting out of place.

Interesting, Porsche took this issue so seriously in ‘80 they published this:
“NOTE: Only the approved belt form Goodyear, Part No. 999.192.176.50 may be used.
The new belt must be tightened more than previously.
Adjustment: Tighten belt as usual (10 to 15 mm deflection). Then reduce the number of spacers between the pulley halves by one (ca. 5 mm belt deflection).”
I think this was to keep the small (84 mm) diameter fan pulley from slipping.

Another issue here is it appears we are close to the limits of fan belts. Clearly a new belt should be run-in and then readjusted. I took racing run-in belts with known number of shims.



Something as simple as pulleys, fan belts, and fans can have a profound effect on a 911 engine.

Best,
Grady

JDUB,

When do you get the 220 degree temps? What type of driving? Do the temps go down when you have air moving past the cooler, but go up when sitting in traffic? Remember 220 isn't too hot under these types of conditions, and you want to get your temps high enough to burn off that "cheese" or "mayo" like substance that some find in their oil because their temps are consistently too low.

If you haven't searched yet, you can find lots of suggestions on various ducts and vents peaole have come up with to add air flow. Some are very inexpensive.

Finally, make sure youe CO and timing are right. If you are running too advanced or too lean, then temps will go up.

What is the "Rubbermaid Solution"?

Never mind, I found it:

http://forums.pelicanparts.com/showthread.php?s=&threadid=150982&highlight=Rubber maid+Solution

I think mine are black, perhaps coated......are they supposed to be bare bronze/copper?

I had an idea, that I have not worked through yet; bolting a perforated brass plate between the trombone opening. The connection points or clamps would have to transfer heat to the plate, I am not sure it will work. I would not want to soder or braze anything until I had some clue as to it's effectiveness.

Is the any chance the mixture is off making it run hot?
-Chris

The problem with the trombone cooler is insufficient surface area. If you braze fins onto the tubes or lengthen the coil, it will dissipate more heat, but it still won't be as efficient as a properly engineered oil cooler.

Sherwood