I'm undergoing an engine rebuild at the moment. If I'm going to address my concerns about a cooler operating 928, now is the time to make the decision. I first asked my mechanic his suggestions and he recommended an aftermarket radiator with increased cooling capacity (I wouldn't have to worry w/ those plastic end tanks either). This is certainly an option, however my concern isn't during open road driving since I haven't experienced unusually high temps then. More specifically, I'm concerned about finding myself in a traffic jam on a hot summer day here in the south. I've watched my 928 climb in temperature rather quickly in the past under these conditions as I'm sure many of you have.

A friend of mine suggested that cooling fans with improved CFMs, instead of the radiator, may be a better option as my concerns are more to address increasing temperatures from sitting in traffic. The temp. quickly returns to normal after I start moving.

Because this rebuild is going to be expensive, I wouldn't want to waste money on a radiator if what I really need is increased CFMs. Any ideas or comments?

My apologies if this has been discussed before. However, my search didn't reveal any real answers.

Thanks,
Nicholas

 

If your temps go down to acceptable levels when you are moving >30mph, then you need to generate more airflow across the stock radiator at slower speeds in order to keep the temp where you like it. Installing a radiator with a larger capacity but leaving the stock fans will just delay the temperature increase, but it will still happen.

Dan
'91 928GT S/C

 

That's what I was thinking. Any suggestions or has anyone purchased an aftermarket fan w/ increased CFM and tested it with success?

 

Best thing I ever did to cool it down was blow all the dirt, dust, bugs, pebbles, and small children out of the radiator and a/c condensor fins. If you have the radiator out, use compressed air to blow all the crap out of the a/c condensor from back to front. If you re-use the old radiator, do the same to it before putting it back in. Made a huge difference for me.

Rich

 

You might also check on a 75 degree thrmostat.

 

Charley, I've got the 75 degree thermostat.

Rich, when I bought it (1500 mi. ago) she was pretty clean, but always worth another look. I didn't check for small children though so I'll have another look.

 

c&r Radiator from 928 intl, well worth the $$

 

Carl at 928Motorsports offers this as a possible solution, along with the 75 degree thermostat.

www.928motorsports.com/parts/auxfan.php

 

Carl at 928Motorsports wrote;
He is certainly correct that fan technology has moved on; do not know how 2000 CFM compares with the current fan but nevertheless this sounds like a good way to go.

Marton

 

The S4 are designed to operate with an engine cooling system at around 87 to 90 degrees C, so a 75 degree thermostat has the potential to have the engine operate at too low a temperature, which can be depremental to the efficient and effective operation of the engine.

If your temperature gauge is raising when car is in traffic, in hot ambient conditions, then there could be numerous problems such as:

Internal jacket water galleries scaled up with deposited salts from the cooling water interfering with the effective transfer of heat from the block and cylinder heads to the cooling jacket water. (drain and pressure flush and refil with recommended coolant additive and consider using a "water wetting additive").

Internal contamination and partial blockage of the radiator galleries causing loss of coolant flow and fall off of heat transfer to the cooling air. (Drain radiator and pressure flush).

External contamination and partial blockage of air way through the radiator fins and over the cooling pipes minimising heat transfer rate. (Remove radiator and clean out air passages by using compressed air, wash with detergent and blow through again. If you use high pressure water be careful as the jet of water can bend the cooling fins).

External contamination and partial blockage of airconditioning condenser restricting air flow to the radiator. With radiator removed clean A/C external surfaces of condenser as described above for radiator).

Foreign matter caught between condenser and radiator restricting air flow. (When radiator removed debris easily removed).

Seal between the engine bonnet and the top of the electric fan shroud causing air flow over top of radiator reducing the air flow through the radiator thereby reducing the cooling effect of the radiator on the jacket water. (This seal can be missing or has gone hard. Replace seal. A suitable seal should be able to be sourced for a automotive supply shop).

The two speed electric fans not operating correctly thereby minimising air flow through the condensor and the radiator. (There has been recent threads written on overhauling these electric fans and the troubleshooting procedure is included in the WSMs and the 1987 Service Information Technik booklet).

The cooling flaps not operating correctly thereby restricting air flow through the condenser to the radiator. (There are numerous threads written about imoblising these fins by removing fuses etc and 'jip' tying them in the open position. I prefer to operate the system as designed. A full operating procedure is described in the WSM and also in the 1987 Service Information Technik booklet together with the troubleshooting procedure).

The radiator temperature and inlet air temperature sensors not operating correctly, which and adversely affect the correct operation of the cooling flaps thereby reducing air flow through the radiator. (Refer to troubleshooting procedure mentioned above).

Thermostat not working correctly and therefore not seating on it seal allowing bypassing of jacket cooling water causing excess engine temperature. Check out operation of thermostat in hot water with thermometer as described in the WSM. Also renew the "O" ring seat and cover "O" ring in its housing. Good R & R procedure recently written up. Do a search on this 928 Forum).

Note: The cooling system is infact a totally operating system that requires all the individual parts of the system to be working correctly and in harmony. It has been designed to achieve a set engine temperature in the shortest period of time, mindful of the the differential expansion of the components in the engine, and to maintain this operating temperature within fixed limits with minimum and maximum ambient air temperatures selected by the designers with a safety factor built in (excess cooling capacity).

I have operated my car in temperature down below zero degrees C and a maximum of over 40 degrees C and my temperature only varies a few degrees, whether in stop of start traffic or freeway driving in summer or winter.

I would suggest that all of the above items should be checked before undertaking design changes to the system, such as fitting lower temperature thermostats, increasing the fan size to increase the CFM air flow or increasing the size of the radiator as the system may only need some TLC via some good R & R.

Tails 1990 928S4 Auto

 

Tails, you seem to really know this stuff. What about the 85/86 engines? When mine started sticking, I was given what must be a 75°. The old thermo ran in the upper middle of the gauge. Now at operating temp, it is rarely more than one needle width above the first line, which much cooler. I've wondered if it might be too cool. Thanks.

 

FWIW I have undertaken nearly all of the above described by tails on my 87. AC condenser and Aluminum radiator are both reletively new and clean. Thermostat is new and I do not have cooling flaps installed the the car anymore. I was experiencing very warm running here in the texas summer. I drained the coolant out, filled the sytem with water and got the car get to operating temp for a few minutes until the t-stat opened and cycled fluid. I then drained the water and repeated the process twice more. I installed new mixed rad fluid with some water wetter. Engine runs MUCH cooler now in traffic. Old rad fluid was 3 years old. The car now runs a smidge above the center mark on the guage in 100 degree temps with AC on.

 

Engines with a oil cooler, (32Vs/euro 16V), have an oil thermostat, which means the block will never get too cold. Without an oil thermostat, I don't think I'd run the 75C.

With a 75C t-stat installed, my '86 block stays right around 87C (188F), versus 91C+ (195F+) with the 87C t-stat. I can run much more ignition (and cam) advance with the colder t-stat.

 

Has anyone tried "40 Below"? I used it years ago in a trans am motor with good results. I wonder if it would be safe is an all aluminum Block???

 

Thanks guys for your comments and especially Tails for your voluminous content; that was good reading. The car isn't with me as it is having an engine rebuild. I decided to go ahead with a replacement aluminum radiator if, for no other reason, than to have a brand new component accompany my brand new engine. That radiator is approaching 20 years soon and I would hate to get the car home and w/in a couple year's time start to experience problems like end tank leaks, etc only to have to remove the radiator and start over again with this dilemma.

If I still have a problem after the fact, I will look more closely at the other areas of concern that you guys have outlined. I would do it now, but I just don't have the car w/ me. I'm especially intrigued by the higher CFM cooling fans, although Mark A. reports that the factory component does a pretty good job.

I do know that I have the 75 degree thermo., my cooling flaps have been fixed open, the radiator fins are very straight and clean. If it weren't for the dull color, the radiator would look almost new externally.

Thanks,