924Board.org

bryanc · Joined: 27 Feb 2003 Posts: 233 Location: San Antonio, Texas

Things were looking good. A little acceleration problem to correct then BANG the darn thing starts overheating.
Here's what happened.
Long story but I replaced the head (reworked by the shop recommended by the local 924 guru) and everything seemed OK on a few test runs but then I took it out on the freeway and the temp seemed OK for the first few miles but then climbed up to the "red zone" and hovered there.
Here is what I have done so far:
Rechecked the cam timing
Rechecked the valve clearance
Rechecked the ignition timing
Refilled the cooling system after letting it get hot.
The only strange thing I have found is that at idle if I remove the vacuum advance there is no change (that seems OK) but if I remove the vacuum retard the timing changes maybe 10 degrees (that doesn't seem right)
Does removing the vacuum retard change the timing at IDLE?
Forget about the timing, is anyone aware of problems with blocking coolant passages when using a 79 head on an 82 block (n/a) or gasket sets blocking coolant passages. I seem to remember a gasket lining up with one of two holes on the head.
Any tests to find the problem or experiences with this type problem would be appreciated

_________________
'84 944
I'd rather have a bottle in front a' me than a frontal lobotomy
Tom Waits

78porsche924 · Posted: Sun May 04, 2003 3:09 pm Post subject:

Are you loosing coolant? It could be a bad water pump or a blocked radiator or something. And is the 79 head the same as an 82? I know the valves changed but i believe that was 77.5. They got bigger. Flushing out my coolant system and refilling it did wonders for my temps but i assume that u did that considering you replaced your head. Are you running rich at all because that helped my heat issues too once that was fixed.

bryanc · Joined: 27 Feb 2003 Posts: 233 Location: San Antonio, Texas

I am not loosing coolant except for when it finally gets so hot the cap lets some coolant out.
I have tried making the mixture richer with very little change.
Just so you know, I have replaced the hose on the top of the engine temporarily with an "Auto Zone as close as I can pick it off the rack" replacement. The only difference is that there is no air bleed on the replacement but after refilling the cooling system and then later removing the hose, it is full of water/antifreeze mixture which says to me that bleding the air is not the problem.
Since this whole problem started with oil in the coolant (that's why the head was replaced) a coolant system flush was the first thing done after replacing the head.
_________________
'84 944
I'd rather have a bottle in front a' me than a frontal lobotomy
Tom Waits

924martinirossi · Posted: Sun May 04, 2003 4:22 pm Post subject:

The rubber hose with the bleed valve will be mailed to you on Monday.

Michael

wdb · Joined: 02 Nov 2002 Posts: 2024

possible causes of overheating . this is not 924 specific , general automotive trouble shooting . a link to 924.org FAQ about trouble shooting the cooling fans .

http://www.924.org/techsection/GarageFAQ.htm#radfans

since you mentioned your timing was retarded, and it is in the list, probably should start there , disconnect your retard vacuum line from the distributor,PLUG the line so you dont have a vacuum leak, and take the car for a short gentle ride and see if the car over heats , if ithe car doesnt overheat , take it for a longer ride . Maybe your static timing setting is too close to TDC or retarded and the vacuum retard is retarding the timming too much/far . maybe try advancing the timing a few degrees before TDC and reconnect the retard vacuum line and see if that clears it up .

924martinirossi · Posted: Mon May 05, 2003 3:43 am Post subject:

I use straight water only and my car runs at the first mark or below. In stop and go traffic or in a traffic jam the temp will slightly go over the second mark then drop back down.

When I was going thru the heating problems with my 80 931 I found the radiator was leaking but not so much as to cause water evidence on the ground. I finally noticed that a part of the radiator was wet when the car was overheated and blew the recovery tank, twice. The radiator was so hot that the fluid evaporated right off it. Prior to that I replaced the water pump (just because I can). I then replaced the radiator and all was fine.

After the engine has warmed up check to see if the water is being pumped to the overflow/expansion tank.

You can check the operating temp of the thermostat by attaching a string to it and putting it in water along with a thermometer as you heat up the water the thermostat will open up at some point. Check this opening point with the water temp. Somtimes the operating temp. is stamped on the thermostat housing.

The radiator fan is only effective at speeds under 30 mph. At 30 mph and above their is enough air flow thru the radiator to cool.

Remove some of the coolant hoses and back flushing the system might help.

Michael

bryanc · Joined: 27 Feb 2003 Posts: 233 Location: San Antonio, Texas

* Faulty radiator pressure cap (low pressure causes coolant to boil )
If I remove the cap when hot the coolant will start to boil, to me this indicates the cap is holding presure

*Defective thermostat (if stuck open, coolant does not stay in radiator long enough to cool down . If stuck closed , coolant does not flow though the system.)
Thermostat was tested per Haynes

*damaged ,faulty or non running cooling fan .
Fan motor was recently replaced and I get a good flow or hot air when running

* Collapsed lower radiator hose .
visual check, good

*Clogged radiator fins ( oil dirt bugs )
The radiator was removed from the car when the head was replaced and checked for blockage, none visable
*Clogged A/C fins (oil dirt bugs)
Aftermarket AC (134a system) I will double check.

*Clogged radiator tubes (inside the radiator) , corrosion , scale , sludge from anti-freeze getting into the crankcase and oil.( milky looking oil ) If this happens the engine oil system should be flushed ,the sludge can block some oil passages and ruin the engine ,there are a number of commersial products for this .

When the radiator was removed the drain plug threaded hole had a crack between it and the radiator wall. This was soldered but the rest of the radiator went unchecked by the shop. Since my original problem was oil in the coolant there may have been a buildup of sludge. The first thing I did when the engine was reassembles was to run a radiator flush (Prestone super radiator cleaner) and it says it removes rust and OILY DEPOSITS. How well, I don't know. This may be worth a recheck.

*Defective water pump

It worked befor the head was replaced and there are no leaks

*Low coolant level

no

*water used as coolant ,no anti-freeze , low boiling point .

no

*coolant system capacity inadequate for load, ( need to upgrade to a 5 core radiator)

It was OK before

*Air trapped in cooling system

That will be checked (thanks Michael)

*Clogged coolant passages in engine block (flush radiator with anti corrosion products )

Maybe the super flush didn't get it all. I will reflush if there is no way to test or check to see how well the original flush worked. By the way the lower radiator hose gets hot when the engine is running (indicates coolant flow).

* Excessive use of A/C while vehicle is parked or in stop and go traffic .

It overheats with or without the A/C on.

*Retarded Ignition timing .

The timing was set using the "under the hood procedure" (sticker on the drivers side fender). The question I had was whether the vacuum retard should have an effect at idle. Since there are no devices between intake manifold and the dist. I assume this is not the problem.

*ignition timing too far advanced .

See above.

*Clogged exhaust system .

Hmm, I did replace the exhaust manifold with the head and beat on the Catalytic Converter (to align it level with the car) there may be something to this.

*Low engine oil level .

No way

Excessive engine friction (using too thin oil like 5W or old oil needing to be changed )

Correct Oil but new rings and rod bearings but what seems to get the hotest is the head, not the lower engine.

*Dragging brakes .

Nope.

What this leaves me with is the following:
Blocked radiator or engine passages but a chemical flush was used but I can always try a second time. Maybe the backflush is the way to go.

Blocked exhaust system. Does anyone have a test for this?
By the way I did a compression test and got 130 - 135 per cyl.
[/b]
_________________
'84 944
I'd rather have a bottle in front a' me than a frontal lobotomy
Tom Waits

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

hey 924martini- you should use some of redline's water wetter if you're using straight water and no coolant. coolant actually has some lubricating properties for the waterpump bearings and such. water wetter is meant to keep the lubrication when you're running straight water.

i think having trapped air is a likely suspect if you haven't been able to bleed the system using the bleeder on the hose you replaced. it can really make the gauge rocket up into the red if you've got air in the system.

good luck with the diagnosis,
-nick

924martinirossi · Posted: Mon May 05, 2003 6:15 am Post subject:

I have used the Redline Water Wetter past in my Martini Rossi. Stuff really did lower the temp. I guess I have to find some or try some of the stuff that they sell at Schucks.

Michael

78porsche924 · Posted: Mon May 05, 2003 8:44 am Post subject:

www.performanceproducts.com has the water wetter i know.

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

When you ran the flush through did you leave the thermostat installed? If you flushed it without the thermostat, the flush just stayed in the block and didn't get to the radiator.

Dennis
_________________
81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

bryanc · Joined: 27 Feb 2003 Posts: 233 Location: San Antonio, Texas

Dennis said,
"If you flushed it without the thermostat, the flush just stayed in the block and didn't get to the radiator."
Visa versa I think.
Anyways the flush was a chemical flush and the instructions said to run it between 3 and 6 hours so yes the thermostat opened and the flush went throughout the entire cooling system (I even opened the heater valve).

I am starting to suspect maybe more than one problem.
Here is why:
The lower cowling/air dam was missing and was replaced. The air conditioing 134a coolant was bled out and replaced due to a rerouting of the freon hoses to allow the install of the air dam. The radiator was removed and reinstalled with the A/C condensor coils in a slightly different, more like stock, position (A/C shop just mickeymoused it in). That upper radiator hose was replaced (temporarily) with a hose without an air bleed. I shortened the hose by just a few inches and now it only overheats when I turn on the A/C (at least thats what it did last test drive).

Can too much freon (134a) cause the engine to overheat. The sticker on the A/C said 1KG and I put in 3- 12oz cans. I don't have a high side guage to make measurements but the low side is 35 lbs and static at 90 lbs.
Could the air dam (lower valance) cause this much of a change?
_________________
'84 944
I'd rather have a bottle in front a' me than a frontal lobotomy
Tom Waits

bryanc · Joined: 27 Feb 2003 Posts: 233 Location: San Antonio, Texas

I found it.
DC fan motors.
If you wire them backwards they try to push air out the front of the car.
If you drive your car foreward this is a bad thing.
Swapped the wires (20 year old connectors to the fans were replaced with faston connectors) so it was easy to get them reversed.

At least it didn't cost much to fix it.
_________________
'84 944
I'd rather have a bottle in front a' me than a frontal lobotomy
Tom Waits

Roger · Joined: 06 Jan 2003 Posts: 1235 Location: Cordova, TN

Fairly common problems with the 924's are:

Fans check to make sure they are both operating at the same speed. I am not sure but if you measure the amp draw it should be the same for booth fans. Also make sure to check relays and fuses. I had to have one fan replaced when my car was running hot.

Temp switch do booth fans come on when the temp rises? If not do both fans come on when the A/C is turned on? If the fans only operate properly with the A/C on its most likely the temp switch.

Water pump I couldnt tell you how to check this an a 924 since they are fairly well burried, but I dont think they have to leak if they are bad. I have heard that they will make a graoning noise if they are on the way out.

Thermostat check to see if your radiator is geting hot evenly. It feels cool the thremostat could not be allowing he coolant to circulate properly. Also uneven heatinf of the radiator could mean its cloged.

Ballast resistor could be bad but this usually only effects the slow runing of the fans after he engine has been turned off.

Running hot or overheating can kill the head. I would strongly suggest that you correct the problem. The heads on our cars are really suseptable to warping or blowing the head gasket.
_________________
1981 924 NA

Some people are like Slinkies. Not really good for anything, but you
still can't help but smile when you see one tumble down the stairs.

bryanc · Joined: 27 Feb 2003 Posts: 233 Location: San Antonio, Texas

Just to follow up.
I drove the car for a couple of hours today and spinning the fans the right way cured the problem. Stays between the 1st and 2nd marks even at 96 degrees ambient.
When I got the car the engine cooling fan was inop. I looked at OEM ($$$) and then took the whole fan assy to NAPA autoparts. After a brief search of their stock I found a motor that was a physical twin of the OEM motor ($25.00) but the shaft did not have a flat machined on it. 5 minutes with a grinder took care of that (and a file would have worked if I didn't have a grinder). Other than wiring it backwards I have had no problem with the replacement motor. The AC fan came with the car and has been functional since I got the car.
Now if I can just fix that flat spot in the acceleration.
Manana

_________________
'84 944
I'd rather have a bottle in front a' me than a frontal lobotomy
Tom Waits