Saturday, February 18, 2023

Alfa Romeo GTV6 Transmission Ratios

Alfa Romeo GTV6 Transaxle

 The Alfa Romeo GTV6 transmission gear ratios have been revised a few times during its production life. Using official factory resource materials, here's a look at the various gear ratios used. Before we do, like many things that concern the GTV6, production changes overlap model years. For example, my car is a 1982 model year but has the 1981 transmission ratios. So don't be surprised if a 1984 car has 1983 gear ratios, etc. Typical Alfa.

When the car debuted in Europe in 1980, the ratios were as follows.

Alfa Romeo GTV6 Transmission Ratios (European and Early US Cars)


Final Drive: 4.10:1

(gear ratio / overall ger ratio)

1st: 3.50:1 / 14.350:1 

2nd: 1.956:1 / 8.0196:1 

3rd:  1.345:1 / 5.5145:1 

4th:  1.026:1 / 4.2066:1

5th: 0.78:1 / / 3.198:1   

REV. 3.000 1 / 12.3000

European and Early US Spec Alfa Romeo GTV6 Speeds in Gear*

1st   @1000rpm  4.8mph (7.803kmh)               @6300rpm  30.55 mph (49.16 kmh)

2nd  @1000rpm   8.67 mph (13.964 kmh)        @63000rpm  54.66 mph (87.97 kmh)

3rd  @1000rpm    12.63 mph (20.321kmh)       @63000rpm   79.55 mph (128.02 kmh)

4th   @1000rpm    16.55 mph (26.642 kmh)      @6300rpm   104.29 mph (167.85 kmh)

5th   @1000rpm  21.78 mph (35.053 kmh)        @6300rpm 137.22 mph (220.83 kmh)

RPM @ 60 mph in 5th gear: 2755 rpm 

These were the same ratios used in North America when the GTV6 hit our shores in 1981. Some early 1982 GTV6 models also had these ratios until they were replaced by the noticeably taller ones below.

Alfa Romeo GTV6 Transmission Ratios (1982-1983 US Spec)


Final Drive:  3.42:1

1st  3.500: 1 / 11.958:1

 2nd 1.956: 1 / 6.683: 1

3rd  1.258: 1 /4.298 1

4th  0.946: 1 / 3.232: 1

5th  0.780: 1 / 2.665: 1

REV. 3.000 1 / 10.249: 1

1982-83 US Spec Alfa Romeo GTV6 Speeds in Gear**

1st   @1000rpm  5.82 mph (9.37 kmh)              @6300rpm  36.68 mph (59.03 kmh)

2nd  @1000rpm   10.41 mph (16.76 kmh)        @63000rpm  65.61 mph (105.59 kmh)

3rd  @1000rpm    16.20 mph (26.07 kmh)       @63000rpm   102.06 mph (164.24 kmh)

4th   @1000rpm    21.54 mph (34.66 kmh)      @6300rpm   135.68 mph (218.36 kmh)

5th   @1000rpm  26.10 mph (42.00 kmh)        @6300rpm 164.41 mph (264.60 kmh)

RPM @ 60 mph in 5th gear: 2299 rpm

Some feel that these taller ratios took away the "hot-rod" feel of the earlier car. However, the lower rpms at highway speed were welcomed by many who spent a lot of time on the highway. First gear also became more useful. Zero to sixty times were also improved by eliminating the shift out of second gear before sixty miles per hour were reached.

Alfa Romeo GTV6 Interior

Alfa Romeo GTV6 Transmission Ratios (1984-85 US Spec and Other Markets)

These ratios continued until the 1984 model year, when the 1982 tall gear ratios were combined with the original 4:10:1 final drive. This transmission is referred to in Alfa Romeo documentation as the "High-Geared Gearbox/Differential." 


Final Drive: 4.10:1

1st 3.500:1 / 14.350:1 

2nd 1.956:1 / 8.0196:1

3rd 1.258:1 /  5.1578:1

4th 0.946:1 /  3.8786:1 

5th 0.780:1 / 3.198:1 

1984-85 US Spec Alfa Romeo GTV6 Speeds in Gear*

1st   @1000rpm  4.84 mph (7.80 kmh)              @6300rpm  30.53 mph (49.14 kmh)

2nd  @1000rpm   8.67 mph (13.96 kmh)        @63000rpm  54.65 mph (87.95 kmh)

3rd  @1000rpm    13.50 mph (21.73 kmh)       @63000rpm   85.07 mph (136.90 kmh)

4th   @1000rpm    17.95 mph (28.89 kmh)      @6300rpm   113.10 mph (182.01 kmh)

5th   @1000rpm  21.78 mph (35.05 kmh)        @6300rpm 137.21 mph (220.82 kmh)

RPM @ 60 mph in 5th gear: 2755 rpm

Note: These speeds are based on 195 60 R15 tires for comparison sake and not the TRX Metric  200/60 HR365  tires size standard on the 1985 US GTV6.

Interestingly, while most European cars I've heard of stayed with the original 1980 gear ratios, this "High-Geared Gearbox/Differential" is listed in the European Technical Inspection Manual dated from 3/1984. 

1985.5 ALFA GTV6 Isostatic Gear Shift

 Starting about mid-way through the 1985 model year for US cars (Chassis number 10006731 according to Alfa Romeo documentation), Alfa updated the transmission shift linkage for an improved feel. This revised shift linkage is commonly called "Isostatic ." This modification replaced the simple external shift lever at the transmission case with a series of rods and levers. The consensus at the time was that the revised shifter was smoother, easier, and had a more positive feeling than the rather clunky original shifters. However, nearly 40 years later, Isostatic shifter parts are challenging to source. Because of that, some are saying if you have a worn-out shifter, you are better off now with the old-style shifter mechanism. So much for doing the Isostatic upgrade I never got around to doing!

Update 2-21-2023

I see the Alfa Romeo European Workshop Manual showing 1985 and later European GTV6 models as having the ratios listed below. I invite our European friends to post a comment and let us know what ratios they have in their cars.

Alfa Romeo GTV6 Transmission Ratios (1986 US Spec and late 1985 European Version)

The gear ratios were revised again in 1986. The 4.10:1 final drive was retained, but the first three gears were modified. This close ratio gearbox had less of a gear spread, which is intended to keep the engine in its powerband while accelerating. Now the first four gears were closer without the significant speed gaps of the 84-85 transmission. First gear also returned to being a more useful gear ratio, which many people welcomed. 


Final Drive: 4.10:1

1st 2.875: 1 / 11.787:1

2nd 1.720: 1 / 7.052:1

3rd 1.226 1 / 5.027:1

4th 0.946 1 / 3.879:1

5th 0.780:1 / 3.198:1

REV.  3.000 1 / 12.300:1

1986 US Spec and late 1985 European Version Alfa Romeo GTV6 Speeds in Gear*

1st   @1000rpm  6.00 mph (9.646 kmh)              @6300rpm  37.76 mph (60.770 kmh)

2nd  @1000rpm   10.01 mph (16.123 kmh)        @63000rpm  63.12 mph (101.575 kmh)

3rd  @1000rpm    14.05 mph (22.620 kmh)       @63000rpm   88.55 mph (142.506 kmh)

4th   @1000rpm    18.21 mph (29.315 kmh)      @6300rpm   114.76 mph (184.685 kmh)

5th   @1000rpm  22.08 mph (35.553 kmh)        @6300rpm 139.18 mph (223.984 kmh)

RPM @ 60 mph in 5th gear: 2716 rpm

Update 2-19-2023:

I have found official speeds in gear@1000 rpm and have updated the 1986 numbers. Previously they were calculated.

Let us know if you have more information to share by leaving a comment.  Thanks for reading!



Alfa Romeo Inspection Specifications publications dated 10/1981, 2/1981, 3/1984, 

Alfa Romeo GTV6 Owners Manuals: 1981 through 1986

Alfa GTV6 Spare Parts Catalog, USA edition 0060495165, 9-1989

Alfa Romeo Workshop Manual  PA36090+ 9/84

*Official km/h @ 1000 RPM speeds in gear provided by factory. Converted to mph for convenience.

**Approximate speeds in gear calculated. Factory tire size value used. Rolling radius of tires, among other variables, affects speed. Speeds are rounded for convenience.

Friday, February 3, 2023

Alfa GTV6 Thermostat Replacement

Alfa GTV6 Thermostat Assembly

  A vital part of the Alfa Romeo GTV6's cooling system is its thermostat. Luckily, the GTV6's thermostat is easily accessible on the top front of the engine and can be removed without draining much of the cooling systems. The thermostat comes complete with the housing. If the whole unit is unavailable, people have replaced just the thermostat insert, but that requires modifying the housing. 

A new thermostat assembly does not come with the coolant bleed screw, so make sure you can reuse your old bleed screw off of your old one. If not, order a new bleed screw. In addition, you should also order two new thermostat gaskets (upper and lower) and a bleed screw sealing washer. 

Alfa Romeo GTV6 Thermostat Temperature Specs

  • Initial opening: 180-185°F (81-85°C)
  • Fully open: 200°F (95°C)

Alfa Romeo GTV6 Thermostat Part Number

  • 60558491

Alfa Romeo GTV6 Thermostat Gasket Part Number

  • 60507415 Upper Gasket
  • 60777088 Lower Gasket

Alfa Romeo GTV6 Cooling System Bleed Screw Part Number

  • 60506832

Alfa Romeo GTV6 Cooling System Bleed Screw Washer Part Number

  • 60800596

Alfa Romeo GTV6 Cooling System Capacity

  • 3.2 Gallons
  • 12 Liters

Alfa GTV6Thermostat
Comparison of my original thermostat and the current thermostat being sold at many vendors now.  Make sure you check if the bleed screw on your original can be removed and is not stripped or seized. If it is, you'll need to order a new bleed screw when you order your thermostat. 

A paper gasket seals the thermostat.  Note the hole at 10:00 is the bleeder passage.  It is important to bleed all the air out of a GTV6 cooling system if you want trouble free operation and a cool running car.

GTV6 Lower Radiator Hose
You can drain the coolant out by removing the lower hose connections or...

GTV6 Radiator Drain Plug removing the radiator drain cock on the lower left side of the radiator.


1. Make sure you can loosen the cooling system bleed screw. If this strips or can't be removed,  you will have to buy a new thermostat. 

2. Drain and coolant down below the lower edge of the thermostat housing.

3. Disconnect the upper radiator hose.

4. Unscrew the three securing screws of the thermostat, then remove it with the gasket and bracket.
Take care not to detach the lower gasket between the thermostat intermediate spacer and lower radiator hose adapter. In case you do, that is why you order the upper and lower thermostat gaskets.

Alfa GTV6 Thermostat Hoses
The intermediate spacer is sandwiched between the lower radiator hose adapter and the thermostat. When you remove the bolts that hold down the thermostat, the spacer can come loose if you are not careful. This will likely happen if you do any prying on the thermostat to remove it.  You should replace the two return hoses shown above anyway.

Now is an excellent time to inspect all your hoses if you haven't done that beforehand.

Spend extra attention on the two hoses attached to the thermostat intermediate spacer. This would be the time to change them. 

If you decide to change anything more than the thermostat, remember to drain the cooling system down. You need to take care not to spill anti-freeze on the timing belt if you are not changing it.

Take care not to detach the lower gasket between the thermostat intermediate spacer and lower hose adapter.

Alfa GTV6 intermediate spacer
The thermostat sits on top of this intermediate spacer. This spacer sits on on top of the lower radiator hose adapter below.

Alfa GTV6 Lower Hose Adapter
This is the lower radiator hose adapter that the intermediate spacer is attached to. The screws that hold the thermostat and spacer screw into this adapter. This hose adapter is bolted to the top of the water pump (see below).

Alfa GTV6 Water Pump
The lower radiator hose adapter is bolted to the top of the GTV6's water pump.


Most people just replace a suspected thermostat, but as parts for these cars are not falling off the shelves of local parts houses, it makes some sense to test the thermostat to see if it is bad.

You can check the thermostat by suspending it in a pan of hot water, using a thermometer, and observing the thermostat. Note you shouldn't let the thermostat lay on the bottom of the pan as that can yield inaccurate temperature results.

The thermostat opens when the coolant temperature is between 81 to 85°C (177.8 to 185°F).

The thermostat opens fully when the coolant temperature reaches 95°C (203°F). You should also check the opening movement is greater or equal to 7.5 mm (0.295 in). If none of this checks out, you should replace the thermostat. 

Ever notice that Japanese motorcycles and cars don't leak? Using a premium sealant like the one above will help. This Toyota sealant is called FIPG 103 (Form In Place Gasket) and is manufactured by ThreeBond. You can use it as a gasket maker as well as a gasket sealant.  Toyota FIPG 103/ ThreeBond TB 1207b are the same stuff. ThreeBond also makes Hondabond and Yamabond.

Alfa GTV6 Thermostat Bolt

The Alfa GTV6 Thermostat Bolt.  My GTV6's thermostat was held down by three  7x55mm bolts (measure yours as I've heard some have reported different sizes).  I replace all worn-out cooling system fasteners with fresh ones. Galvanic corrosion caused by dissimilar metals (steel bolt/ aluminum housing) combined with wet coolant can make these bolts a nightmare to remove. You will be glad you used a new bolt with fresh plating and some anti-seize compound the next time you work on your cooling system.


1. Clean the thermostat mounting surfaces. Using a soft scraper and some gasket removal solvent is the safe way. The Alfa's engine is aluminum, and mounting surfaces can be easily gouged and damaged with hard scrapers if you are not careful.

Clean the threads on the bolt and in all the bolt holes. Check to see that the bolts screw in easily. I recommend new mounting bolts if they have any signs of corrosion or deterioration. This is especially important when working on the cooling system, as the bolts can be subject to corrosion. Breaking or stripping bolts can wreck your day.

2. Position the thermostat on the intermediate spacer using a new gasket. I recommend using a high-quality sealant. I use a thin coating (1mm on both sides of the gasket) of Hondabond/ Toyota FIPG 103/ ThreeBonds TB 1207b.

Tighten the three mounting bolts. I recommend anti-seize on these bolts. Remember the coolant temperature switches wire bracket if your car still has one. There are no tightening specs that I could find for these bolts. I use a 1/4-inch drive ratchet, grip it towards the drive end, and tighten it snuggly with one hand. 

 Reconnect the upper radiator hose. Use a new hose clamp.

3. Restore the coolant level.


Sandwiched between the water pump and the thermostat is the intermediate spacer. This spacer has two coolant bypass hoses attached to it that are impossible to change without removing this spacer. It is strongly recommended you change these hoses at every timing belt change (30-40K miles) or at a reasonable time. A thermostat change is also an excellent time to inspect and change these hoses. 

Alfa GTV6 Thermostat Hoses
The Alfa GTV6 thermostat hoses are 25mm / 1 inch inner diameter and approximately 55mm / 2.165 inches long.

These two hoses have a 25mm / 1-inch inner diameter and were initially made from a hose with a reinforced covering. Unfortunately, this reinforced hose is getting challenging to find, and some suppliers have replaced it with a generic, low-grade heater hose. This downgraded hose makes it especially important to inspect these hoses.

When I changed my hoses, my parts supplier was out of the reinforced hose, so I purchased Gates heavy-duty 1-inch heater hose from NAPA. If you elect to go this route, make sure you use heavy-duty hose clamps with this extra thick, reinforced hose.


Alfa GTV6 Coolant Tank Level

  1. Set the heater control to max heat.
  2. Open the cooling system bleed screw.
  3. Fill the expansion tank with coolant. 
  4. Start the engine and run it until the thermostat starts to open and coolant begins to flow from the bleed screw. Immediately tighten the bleed screw once that happens. Protect yourself - hands, face, and arms - from hot coolant, and have a heavy towel handy to absorb the leaking coolant as you open the bleed screw.
  5. Turn the engine off, allow it to cool, and top off the expansion tank.
  6. Start the engine and check if the cooling fans cycle on and off at the appropriate temperature.

The above is the factory way to fill the system. However, you should be prepared for alternative scenarios like the one below.

If the coolant starts flowing out of the bleed screw appreciably while filling the system, tighten the bleed screw and squeeze the radiator hoses repeatedly to burb some air out of the system into the expansion tank. Keep an eye on the expansion tank level as you do this to see if it goes down. 

Next, open the bleed screw again and continue filling the system until full or the bleed screw leaks. Tighten the bleed screw, start the car, then slowly loosen the bleed screw while the engine is running and leave it open until coolant begins to flow. The cooling system will be under pressure when you open the bleed screw, so do it carefully and slowly. Don't be surprised if air/ coolant spurts out, so have a towel over the screw. Coolant gets hot quickly, so also be prepared for that. Tighten the bleed screw immediately, and you should be all bled out. Check the level when cold, and you are done.

Again note:
  1. Have protective gloves, clothing, face/eye protection, and absorbent towels on hand when doing this.
  2. Be careful when working around a running engine.
  3. Never open the bleed screw or expansion tank cap on a hot engine.
  4. Ensure your towel is not too large that it can get caught up in the water pump belt, etc. 
  5. Coolant isn't great on your timing belt or paint. Take precautions to keep it off. The manufacturer recommends rinsing the belt off with water if that happens.

This is how I changed the thermostat on my Alfa GTV6, which is provided for informational and entertainment purposes. If you have any doubts about your ability to perform this work or have any issues, I recommend having it done by a professional. I am not responsible for any issues arriving from you reading this post. Use at your own risk.