High speed cooling issue?

Crazy Horse · 07-21-2009, 12:06 PM

In have recently switched my 83 NA's radiator compressor fan from 3-blade to 6-blade with (almost) outstanding results.

Driving around town, the guage stays around the halfway mark.

I took a long highway trip yesterday. As the day's temperature rose over 95 degrees and I set the car on 70 MPH (with AC on), the gauge rose all of the way up to the 7/8's mark. When I slowed under 55 mph, the gauge goes back to near mid range. Only at steady 70 MPH does it rise to an uncomfortable level.

I have the 83 hose bleeder system, which I think works best. I have bled it properly numerous times. I removed the bellypan and insured that all of the "shark slits" were not dented. I put the bellypan back on. I have a car with only 30,000 miles on it and it looks like it is a month or two off the showroom floor. All hoses are in great shape. I have installed the lower temp fan switch and have new Dextron coolant in the system. Fans are running properly and in the right direction.

Anyone have an idea as to why I am having this high MPH only cooling issue?

The only other thing may be some radiator clogging - is this something that may be problematic at higher speed only?

I get tired of running the heater to save my engine. It is really hot down here in the "Cool Hand Luke" swamps.

bearone2 · 07-21-2009, 01:50 PM

does the temp drop if you turn a/c off at 70?

do you have the low temp thrermostat to go with the low temp switch?

when i put the 6bl/shroud on the old '84, temp would run up to the middle, fan's would come on(i'd hear them) and drop the temp whether idling or cruising.

i didn't have a/c.

Crazy Horse · 02:01 PM

Once I am at 70 MPH for about 30 minutes, the gauge reads at a little over 7/8. If I turn the AC off, the gauge drops almost to the 3/4 mark. If I turn the heater on (with AC off) at 70 MPH the gauge drops to just over the halfway mark.

Yes, I have installed the 160 degree (low temp) thermostat and have confirmed the lower hose is getting hot properly.

Fans are coming on properly - that is not an issue. It's almost as if the fans were getting in the way at higher speeds.

By the way bearone2, I see that you have Arizona listed as your profile address. You didn't have AC? Wow, you are a die hard Porsche fan...

carlege · 07-21-2009, 02:06 PM

im guessing your radiator is clogged not enough flow.

at that speed the fans dont matter.

Thermostat ehhh maybe but i wouldnt install a low tem because your engine is dialed into operate correctly at the stock temp.

Crazy Horse · 07-21-2009, 02:42 PM

I understand the basics and know that at speed the fans don't matter. In searching prior posts, I saw comments from others that lived in 100 degree 75% humidity areas. A couple mentioned that they thought it seemed as if the fans were inhibiting air by being in the way at high speeds.

A car that is "dialed in" to run in temperate zones will, of course, run hotter in tropical zones...

onZedge · 07-21-2009, 03:30 PM

What was the antifreeze mix ratio? 50/50? Or something else?

Crazy Horse · 03:32 PM

Ratio is exactly 50/50...with a bottle of Water Wetter.

flash968 · 07-21-2009, 03:57 PM

you may not be far off from what is going on when you talk about the fans getting in the way - if you upset the airflow pattern, you can essentially do exactly that

many people make the classic mistake of removing the belly pans - those are there to increase negative pressure under the hood and force all the air through the radiator - many people remove them thinking it would facilitate cooling, but in reality it does exactly the opposite

Crazy Horse · 07-21-2009, 04:08 PM

My car runs noticeably hotter at speed without the pan - that's why I made sure all of the slits were straight before putting it back on.

flash968 · 07-21-2009, 04:37 PM

i just read that hthe belly pan was still on - i skipped over that - my bad

it does sound like an efficiency issue though

when was the last time the radiator was boiled out? if tap water was used, deposits very easily could have built up

when you run the engine, and rev it up, do any of the hoses collapse? even though they may "look" fine, old hoses lose their ability to hold shape, and can easily collapse - they are only rated for a few years, and should be changed regularly

have you actually measured the coolant temp? it could be as simple as a faulty sender

Crazy Horse · 04:43 PM

Thanks for your suggestions.

Hoses are new and car only has 30,000 original miles. The radiator has never been boiled out though.

I have measured the temp. Also, you can see the oil lose its viscosity (down from 5 to 4 bar at 3,000 RPMs) as the temp gauge approaches the "white" area.

flash968 · 07-21-2009, 05:24 PM

there is no coolant loss - if there is, you likely have a leak in the head gasket - it will NOT necessarily make it into the oil

there is no oddball aftermarket chip over-advancing your timing

there is no clogged catalytic converter

failing any of those being the problem, i would check to see if it does the same thing at the same rpm as 55 in top gear, but in a lower gear - this will help determine if it is a coolant flow issue, or something else

Crazy Horse · 07-21-2009, 05:38 PM

- I have no coolant loss whatsoever.
- No chip.
- Cat is OK.

Because of the extended time it takes to get up to nominal heat, replicating the 3400 RPM in a lower gear will be an extended chore - but maybe worth all of the effort.

If anyone has encountered this specific issue, I would like to have any input.

Thanks!!!

carlege · 05:45 PM

not on a porsche. but my daily driver had a clogged radiator that had flow issues and on hot days the temp would rise with how fast i was going. Coolant was full. Hence why i mentioned that in my previous post. hope you get it sorted out... report back with what you find.

Crazy Horse · 07-21-2009, 05:47 PM

I think my decision is going to be to pull the radiator and refurbish it, clean the AC fins thoroughly and add two 3000 CFM aftermarket fans.

That will hopefully "fix" it for good.

Any other recommendations?

Thanks to all!

carlege · 07-21-2009, 05:48 PM

sounds like a plan! good luck

zedsn · 07-21-2009, 05:59 PM

Very interesting. I am surprised your still getting hot with the water wetter in there. My ac in the 83 wasn't working and I had the belly pan off the whole time that I owned it but doing 70+ mph at +70 degrees my 944 would only go up a little more than half way. I believe that I had a 180 degree thermostat and had stock fan blades as well. I too would sugest that you pull your radiaitor and inspect it and possibly have it cleaned out inside.

Crazy Horse · 07-21-2009, 06:04 PM

My car does about the same at 70 degrees - it is only when it is above 95 degrees outside and I have the AC on that there is a problem. Even at 88 degrees my gauge reads a little under 3/4.

bearone2 · 07-21-2009, 06:59 PM

Quote:

Originally Posted by Crazy Horse

Once I am at 70 MPH for about 30 minutes, the gauge reads at a little over 7/8. If I turn the AC off, the gauge drops almost to the 3/4 mark. If I turn the heater on (with AC off) at 70 MPH the gauge drops to just over the halfway mark.

Yes, I have installed the 160 degree (low temp) thermostat and have confirmed the lower hose is getting hot properly.

Fans are coming on properly - that is not an issue. It's almost as if the fans were getting in the way at higher speeds.

By the way bearone2, I see that you have Arizona listed as your profile address. You didn't have AC? Wow, you are a die hard Porsche fan...

thanks but i had the '84 in hawaii in '02, traded for a 87 944S in dec '03, t-boned in the S in feb '04, bought the current 87 951/with a/c with the $5k ins money in late feb '04, moved back to phx june 1st, a month ago and drove from longbeach to phx on a day that was 108 when i arrived and the car ran great, 80-85 most of the way.

have you checked to make sure both fans are pulling air thru the rad rather than pushing to the front.

i mention this because when i swapped for the 6bl, one of them was turning backwards and it caused overheating.i just flipped the connector and the problem was fixed.

good luck.

put a piece of paper in front of the rad with fans on and the paper should be pulled into the rad.

Crazy Horse · 07-21-2009, 07:13 PM

I checked the fan rotation by using the tail of a ty-rap. It works very well. I had it reversed at first. The fans are working properly and in the right direction.

I think the humidity here plays a lot on cooling. Those "people sprayers" (misters) that you see in restaurants in Phoenix and Vegas don't work here at all. No evaporation at all.

It's a "wet" heat!