Heat is Lukewarm

[bob928s3]

Blower Heat is Lukewarm when temperature lever actuated to max.

Replaced Coolant - Drained Rad, Block and Flushed
Coolant is 70% (Porsche Brand) 30 % (Distilled Water) Very Cold this Winter.
Replaced Heater Control Valve
Replaced Temperature Control Unit, New Blower Motor Fan
Thermostat is Mahler
Temperature Gage reads below second line when Engine is Hot.

Heat is luke warm.
When slowing down and at a stop, luke warm becomes cool. Why? Water Pump Issue?

Suspect Heater Core and hope not?
Temperature Control Unit - When you slide lever, where does electrical signal go to in adjusting heat? Older Temperature Control Unit was better when temperature lever was maxed. Thanks Rob

[harborman]

Maybe check to see if the heater valve is really opening all the way.
Is temperature gauge accurate?
Is engine thermostat working or stuck?
How are the vacuum and control lines going to the heater and AC controls?
Check for vacuum leaks.
Check engine temp with an accurate gauge.
Check grounds,

Some ideas at least.

[Mrmerlin]

its helpful if you add the year and model and trans type to your post ,

in the mean time you need a WSM and the wire diagram thats in it and to read this

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=0CDgQFjAA&url=http%3A%2F%2Fwww.928gt.com%2FT-WallyHVAC.aspx&ei=0xDlUrS5C7StsQSeh4CACg&usg=AFQjCNELPje_Z70T6sJEBQqPzEyL0qCDLA&bvm=bv.59930103,d.cWc

[MPDano]

Merlin,

I thought they called the 85 an S3 unofficially?

[Mrmerlin]

S3 was for the early 32V engine
S4 was the 87 and newer

[Mrmerlin]

Porsche introduced a refreshed 928 S into the European market in 1980 model year, although it was summer of 1982 and MY 1983 before the model reached North America. Externally, the S wore new front and rear spoilers and sported wider wheels and tires than the older variant, but the main change for the 928 S was under the hood, where a revised 4.7 L engine was used. European versions debuted with 300 PS (221 kW/297 hp), and were upgraded to 310 PS (228 kW/306 hp) for 1984 model year, though it is rumored [and proven on chassis dynamometers] that they typically made around 330 hp. From 1984 to 1986, the ROW (Rest of World) S model was called S2 in UK. These cars used Bosch LH-Jetronic fuel injection and purely electronic Bosch ignition, the same systems used on the later 32-valve cars, though without the pollution controls. North American-spec 1983 and 1984 S models used, among other differences, smaller valves, milder camshafts, smaller diameter intake manifolds, and additional pollution equipment in order to meet emissions regulations, and were limited to 234 hp (174 kW/230 PS) as a result. Due to low grade fuel 16V low compression S engine was made for Australian market in 1985 model year. It had 9.3:1 compression ratio pistons instead of normal 10.4:1 but used same large intake, high lift cams, large valves etc. what other period ROW S engines used.

As the faster ROW or "Euro" model was not available in the United States and Canada during the first three years of its existence, a "Competition Group" option was created to allow North American customers to have an S model lookalike with spoilers, 16" flat disc wheels, sport seats, sport springs and Bilstein shocks. Customers could specify paint and interior colors the same way as on a normal 928. Two cars were made in late 1980 model year for U.S. with this option. The package was officially available in 1981 and 1982 model years and was canceled in 1983 when the S model became available for these markets. Many cars have had S model features added by subsequent owners, making original "Competition Group" cars difficult to distinguish without checking option codes.

In 1982 model year, two special models were available for different markets. 202 "Weissach Edition" cars were sold in North America. Unusual features were champagne gold metallic paint, matching brushed gold flat disc wheels, two-tone leather interior, a plaque containing the production number on the dash and the extremely collectible three-piece Porsche luggage set. It's believed these cars were not made with S spoilers even though these were available in U.S. during this time period as part of the "Competition Group" option. The "Weissach Edition" option was also available for the US market 911 in 1980 model year and 924 in 1981 model year.

141 special "50th Jubilee" 928 S models were available outside the U.S. and Canada to celebrate the company's 50 year existence as a car manufacturer. This model is also sometimes referred to as the "Ferry Porsche Edition" because his signature was embroidered into the front seats. It was painted meteor metallic and fitted with flat disc wheels, wine red leather and special striped fabric seat centers. Similar 911 and 924 specials were also made for ROW markets.

Porsche updated the North American 928 S for 1985, replacing the 4.7 L SOHC engine with a new 5.0 L DOHC unit sporting four valves per cylinder and producing 288 hp (215 kW/292 PS). Seats were also updated to a new style. These cars are sometimes unofficially called S3 to distinguish them from 16-valve ROW "S" models. European models kept a 4.7 L engine, which was somewhat more powerful as standard, though lower 9.3:1 compression 32-valve engine together with catalytic converters became an option in some European countries and Australia for 1986. In 1986, revised suspension settings, larger brakes with 4-piston calipers and modified exhaust was installed on the 928S, marking the final changes to old body style cars. These were straight from the 928S4, which was slated to debut a few months later. These changes came starting from VIN 1001, which means that the first thousand '86's had the old brakes, but later cars had the later systems. This later 1986 model is sometimes referred to as a 19861⁄2 or 1986.5 because of these changes. The name is a little misleading as more than 3/4 of the 1986 production had these updates.

The 928 S4 variant debuted in the second half of 1986 as a 1987 model, an updated version of the 5.0 L V8 for all markets producing 320 PS (235 kW/316 hp), sporting a new single-disc clutch in manual gearbox cars, larger torque converter in automatics and fairly significant styling updates which gave the car a cleaner, sleeker look. S4 was much closer to being a truly world car than previous models as only major differences between ROW and US models were instrumentation in either kilometers or miles, lighting, front and rear bumper shocks and the availability of catalytic converters in many ROW markets. The Australian market version was only one with different horsepower rating at 300 PS (221 kW/296 hp) due to preparation for possible low grade fuel. Even this was achieved without engine changes.

A Club Sport variant which was up to 100 kg (220 lb) lighter became available to continental Europe and U.S. in 1988. This model was watered down version of the 1987 factory prototype which had a lightened body. Also in 1987 the factory made four white lightened manual gearbox S4 models for racecar drivers who were on their payroll at the time. These were close to same as later actual Club Sport models and can also be considered prototypes for it. An SE (sometimes called the S4 Sport due to model designation on rear bumper), a sort of halfway point between a normally equipped S4 and the more race-oriented Club Sport, became available to the UK. It's generally believed these Porsche Motorsport-engined cars have more hp than the S4. They utilize parts which later became known as GT pistons, cams and engine ECU programs. Some of them had stronger, short geared manual gearbox. The automatic gearbox was not available.

For the 1989 model year, a visible change inside was digital trip computer in dashboard. At the same time Australian models received the same 320 PS (235 kW/316 hp) engine management setup as other markets. Porsche debuted the 928 GT in the late winter 1988/89 after dropping the slowly selling CS and SE. In terms of equipment, the GT was like the 928 SE, having more equipment than a Club Sport model but less than a 928 S4 to keep the weight down somewhat. It had the ZF 40% limited-slip differential as standard like the Club Sport and SE before it. Also like the CS and SE, the GT was only available with a manual gearbox. ROW 1989 CS and GT wheels had an RDK tire pressure monitoring system as standard. This was also optional for the same year ROW S4. For 1990 model year Porsche made RDK and a 0-100% variable ratio limited-slip called PSD (Porsche SperrDifferential) standard in both GT and S4 models for all markets. This system is much like the one from the 959 and gives the vehicle even more grip. In 1990 the S4 was no longer available with a manual gearbox.

The S4 and GT variants were both cut at the end of 1991 model year, making way for the final version of the 928. The 928 GTS came for sale in late 1991 as a 1992 model in Europe and in spring of 1992 as an early 1993 model in North America. Changed bodywork, larger front brakes and a new, more powerful 5.4 L, 350 PS (257 kW/345 hp) engine were the big advertised changes; what Porsche wasn't advertising was the price. Loaded GTS models could eclipse US$100,000 in 1995, making them among the most expensive cars on the road at the time. This severely hampered sales despite the model's high competency and long standard equipment list. Porsche discontinued the GTS model that year after shipping only 77 of them to the United States. Total worldwide production for all years was a little over 61,000 cars.

Second-hand models' value decreased as a result of generally high maintenance costs due largely to spare parts that are expensive to manufacture. The earliest versions, however, especially those models with the Bosch K-Jetronic (CIS) injection system, have few electronic components and therefore can be repaired more easily provided spare parts can be found. Parts suppliers supported by various enthusiasts exist especially in the United States.

The GTS model has retained a high value however, and as of 2006 the price for all variants is apparently starting to creep upwards (Classic Motorsports, March 2006 issue, p. 38).

With the release of the Cayenne SUV, Porsche has met with renewed success with a front-engined, V8-powered model. The company's 2005 announcement that a new V8-powered 4-door grand tourer model called Panamera would be launched in 2009 fueled rumors and fan speculation of a reborn 928. Although the Panamera will be a 4-door model, Road and Track magazine published a speculative piece in their April 2006 issue regarding the possibility of a new, 928-esque coupe that may debut on a shortened version of the Panamera's platform sometime around 2011 or 2012 model year. As of January 2013, no announcement has been made by Porsche that could add credibility to this speculation.

[syoo8]

I have had this problem. What I found- in both of my cars, is that the thermistor that lives underneath the driver's side headlamp goes bad from years of exposure to the elements. You can get those from 928Intl used.

When you mean temperature control unit, are you referring to the mixer motor that adjusts the flaps- the one under the steering wheel?

[Chalkboss]

The stepping motor may need to be adjusted (under steering wheel on right side). I found on my 87 the insulation had degraded on the flaps such that flaps would not close all the way. You can take up the slack by turning the threaded rod to close the flaps fully.
I was tipped off by a bunch of black crap (dust) blowing out of the vents...

[Danglerb]

Originally Posted by syoo8

I have had this problem. What I found- in both of my cars, is that the thermistor that lives underneath the driver's side headlamp goes bad from years of exposure to the elements. You can get those from 928Intl used.

The one in the tube connected to the cool air duct for the alternator.

Coolant path for the heater is the 1/4 cylinder head through the vacuum controlled valve at the firewall, heater core, then I think returns to overflow tank?

Anyway I get heat on both of mine almost immediately after starting the car and driving like a block. Should work fairly independently of the rest of the system. Heater valve at the firewall fails open, so too much heat is the usual issue.

[Alan in AZ]

Originally Posted by syoo8

I have had this problem. What I found- in both of my cars, is that the thermistor that lives underneath the driver's side headlamp goes bad from years of exposure to the elements. You can get those from 928Intl used.

In max heating mode (temp slider all the way to the right) the sensor loop is bypassed - you just get unconstrained heating - mixing flaps to full heat, water valve open. You don't even need an external sensor to get full heat. So I don't think its that (or not that alone anyway).

I'd be checking that the heater valve opens, or maybe manually operate it (disconnect vacuum source - its default state is open).

Also take off the drivers side console carpeted side panel - and look at the setting motor (directly drives the heater core bypass/mixing flaps) - does it move when you change temperature control posistions from max cold - max heat.

Otherwise you may have a clogged heater core...

Alan