ST1100 Coolant Hoses & Timing Belt

Rob Parker posted the following useful parts list a while back. (Thanks, Rob!) I recommend you verify that the numbers are up-to-date when you buy your parts. John Oosterhuis provided the schematic. (Thank you, too, John.) The schematic shows all but the upper radiator and reservoir hoses

Coolant hoses except for upper radiator and reservoir hoses


Now for Rob's write-up:

"I replaced my thermostat because it was not always working properly.

The following is a list of parts that I used in replacing the timing belt and coolant system seals and hoses on my 1993 ST1100P. Prices were from Service Honda in Feb, 2001."

Note: Prices were updated in January, 2014.

Part numbers for cooling system major service.
16211-MT3-000 carburetor insulators (4) $36.36 optional but recommended
91315-MT3-003 water pipe seal (1) $2.53 [13]
19300-MG9-000 thermostat (1) $29.39  
91307-MB0-003 o-ring (54X2) (1) $1.92 thermostat
19503-MT3-000 upper radiator hose (1) $12.35  
19505-MT3-000 lower radiator hose (1) $12.16 [2]
91331-PC9-003 o-ring (21.2X2.4) (2) $3.66 [14] cyl. head hose fittings
91311-KE8-000 o-ring (47.5X2) (1) $1.33 [12] engine block inlet fitting
19504-MT3-000 hose (1) $17.66 [1] LH cyl. head to thermostat housing
19506-MT3-000 hose (1) $15.41 [3] RH cyl. head to thermostat hsng.
19520-MT3-000 oil cooler hose (1) $17.66 [9]
19525-MT3-000 oil cooler hose (1) $26.74 [11]
95005-55003-20M bulk hose (5.5X3000)(1) $16.63 [16] by-pass & coolant reservoir
  total $193.80  
18604-MT3-730 tube, air suction valve $9.33 *

* Note: the last item is a recent addition to the list. Mark Perry had a tough time working with the age-hardened and -bonded part on his 12-year-old bike. He suggested adding it to the list so you could simply cut it and not have to worry about damaging it or other parts while trying to salvage the old one. It is shown as item #6 at this site.

Part numbers for timing belt replacement.
14401-MT3-004 timing belt (1) $89.39
22862-MW7-650 clutch slave cyl. gasket (1) $3.21
18392-MJ4-670 rr. muffler gasket (1) $9.95
18291-MT3-000 exhaust pipe gasket (2) $6.88
  total $109.43

Only the early years of the ST1100 had oil coolers, so you may not need the two oil cooler hoses in Rob's list. I don't know when Honda deleted the oil cooler, but it was not present on the 1996 model.

Yes, the last hose (item 16) is for 3000 mm of 5.5 mm inside diameter hose. There is a 15" length that goes from the thermostat housing to an attachment on the water pipe. Some people use this same material for the hose going to the coolant reservoir. However, I noticed that the coolant reservoir hose is a larger size, about 8 mm inside diameter. I decided that stretching the 5.5 mm hose over 8 mm attachments would lead to early failure, so purchased some 5/16" hose locally. The only hose I could find that size was reinforced fuel line, which is much thicker than the original hose. I added some plastic "snake skin" to protect it from abrasion for about a foot near the forward end.

The part number for the coolant reservoir hose is 19103-MT3-000 and costs $20.63. It is a single wall rubber hose with a plastic sleeve covering about 2/3 of its length.

I also took Bud Couch's advice and substituted 3/4" heater hose for the right-hand cylinder head to thermostat housing hose. By carefully selecting the length, this hose doesn't kink. Shorter is better than longer, I found. The hose just makes a 90 degree bend.

I did not order the exhaust gaskets (I didn't disturb the exhaust joints) nor the timing cover gasket (I re-used the old one).

You'll have to pull the carbs as part of this procedure. Look here for tips on pulling them (under Method 3 of the leak fix procedure).

Tip #1: Sketch or photograph the hose routing, especially those atop the engine, before disassembly.

Tip #2: It isn't possible to remove the water pipe from the engine, because a bolt through a mounting tab can't be taken out unless the timing belt rear housing is removed. But an open end wrench can loosen this bolt, allowing the pipe to pivot around this bolt. After removal of the bolts securing the water cover, it can be pulled off the water pipe for seal replacement.

Tip #3: I used silicone grease on the water pipe seal to facilitate assembly. I also used it on all the hose connections for the same reason. Some of the hoses are a tight fit onto their fittings, especially the two main radiator hoses, and I didn't want to force things and perhaps damage the radiator. For the same reason, I cut the old hoses off the radiator, since they were really stuck in place.

Tip #4: I used silicone sealant on the O-rings for the water joints which attach to the cylinder heads. There was a lot of corrosion in these joints, and I had to use my Dremel with its wire brush attachment to clean the fittings. Hopefully, the sealant will prevent more corrosion. Oddly, the water cover had none of this corrosion. Maybe the water joints are a different material. Note: do not use excessive quantity of the sealant.

Tip#5: The fitting on the thermostat housing for the coolant reservoir hose was somewhat corroded. After I cleaned it up, it was a bit lumpy. I used a worm drive clamp here instead of the wimpy spring wire clip original to the bike. Of course, the 5/16" fuel line was too fat to use the Honda clamp, anyway.

Tip#6: Tim Shevlin submitted this tip for thermostat replacement (Thank you, Tim!):

"Well, as usual, the book procedure is overkill. You need only remove the right pocket fairing and baffle to access the thermostat housing, however it is necessary to remove the lower 10 mm hex bolt by feel, as I recall. I use a 1/4" dr. deep socket for both bolts. The rubber gasket is usually re-usable. A good inexpensive aftermarket thermostat is Stant #35868--about $4 everywhere. I am not sure why the Honda unit is so special, although I did have one fail open on my '91. I don't know if the Stant unit fails open, but I and others have used them on many ST's for several years without a failure. If you use it, leave the brass bubble breaker installed and place the bypass hole at the top. (you may even find warm-up to be slightly faster, as the weep hole is smaller than the open hole in the Honda part, through which flows an amazing amount when the thermostat is closed)".

A number of liSTers have found alternatives to the Stant #35868. J. Plummer found the Stant #13868 (same part except for packaging). Cory Vokoun found an "equivalent" t-stat made by "Murray Plus+" part #3868. John Parker found NAPA 535080, a "Superstat" made by Stant. As John also found out, the application for this part is the 1973-1980 Honda Civic 1.2L, 1.3L & 1.5L, with a 180 degree rating. Knowing the application means you can likely find what you need at most any auto parts store. (Good information, all.)

Be sure to replace the thermostat O-ring when you replace the 'stat. The part number is shown in the listing near the top of this page.

Tip#7: The Honda service manual says that the clutch cover must be removed in order to get the timing belt cover off. Not true, thanks to Jeff Bertrand's explanation:

"Loosen the two clutch cover bolts where that cover overlaps the timing belt cover. You can then kinda pry the cover upward with a screwdriver wedged between the rib on the timing cover and the edge of the clutch cover. You will have to work a little to get the cover up over the crank pulley bolt, take the little timing cover off so you can see what you are doing. A little wiggling pulling a cussin' and you'll have it out. Once out, I took a Dremel to mine and carved a notch in the plastic to clear that bolt. This simplified reassembly and should make removing it the next time much easier."

Tip#8: Another good tip from Jeff Bertrand:

"A good task that should be added to the list when replacing the radiator hoses is to remove and apply thread locking compound to the fan nut, just to be sure. When I had my '93 apart earlier this year my fan nut was fine but I'd heard enough of the stories ... that performing this procedure seemed like a good idea."

Tip#9: Make sure you use silicate-free coolant. Use the Honda stuff or either Texaco or Prestone long-life (5-year) coolant. Anything else will wipe out the water pump seal.

Tip#10: Good tips on substitute radiator caps -- First, from Jay Plummer:

"I've been fighting a constant overheating problem on my 94 ST for a while. All the time replacing the normal stuff that was suggested by the list. Replaced the overflow hose, thermostat and today the radiator cap. The cap was the fix. The rubber washer on the cap was cracked which kept the cap from holding pressure. The good news was a perfect fit was found at Pep Boys. The Stant 11233 model for 7 bucks. This one fit without any modifications. I now have a very COOL ST1100. But we all knew that!!"

Dave Neuchterlein follows with:>/P>

"Gates part number 31336 ...a direct replacement for the STANT number 11233."

The NAPA cross reference for 31336 is BK 7031406, and the listing for BK 7031406 shows a photo of the Stant 11233.

As in the discussion about the thermostat, the application is what you need to know. In this case, John Parker found that was the 1992-1996 Honda Accord 2.2L.

Photos! John Oosterhuis has posted some nice pictures which will help you do the hose replacement at

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Last updated on January 30, 2014     © 2002-2014 M. E. Martin, all rights reserved.