Volvo Penta Thermostat Housing to Heat Exchanger Hose 859800 | MD22 TMD22 TAMD22
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Part Number: 859800
Brand: Volvo Penta (OEM Genuine)
Official Part Name: Hose
Application: Thermostat housing to heat exchanger cooling connection
Supersedes: 859808
Genuine Volvo Penta 859800 is an OEM cooling system hose that connects the thermostat housing to the heat exchanger on selected Volvo Penta MD22, TMD22, and TAMD22 marine diesel engines. It is part of the engine's closed-circuit cooling system and is used with hose clamps 961670 in applicable assemblies. 859800 supersedes the earlier Volvo Penta hose 859808.
Compatible Applications
- Volvo Penta MD22
- Volvo Penta MD22A
- Volvo Penta MD22A-A
- Volvo Penta MD22L-A
- Volvo Penta MD22L-B
- Volvo Penta MD22P
- Volvo Penta TMD22A
- Volvo Penta TMD22-A
- Volvo Penta TMD22B
- Volvo Penta TMD22P-C
- Volvo Penta TAMD22P-B
- Confirm complete engine model and cooling system diagram before ordering — the MD22/TMD22/TAMD22 family used different hose routing and heat-exchanger arrangements across variants
Engine Family: Volvo Penta MD22 / TMD22 / TAMD22 marine diesel
System: Closed-circuit engine cooling
Diagram Position: Thermostat housing outlet → heat exchanger inlet connection
Used With: Hose clamps 961670 (confirm quantity per applicable diagram)
Superseded / Alternate Part Numbers
- Current OEM: 859800
- Supersedes: 859808
When to Replace
- Cracking, surface checking, or hardening of the hose wall
- Loss of flexibility or swelling
- Soft spots or deformation under normal operating pressure
- Coolant seepage at the hose body or clamp areas
- Abrasion, chafing, or physical damage
- Deterioration discovered during thermostat or heat-exchanger service
Service Interval
Inspect all cooling hoses during annual engine service and whenever the cooling system is drained or opened. A hose that has hardened, softened, or shows surface cracking should be replaced regardless of whether it is actively leaking. Coolant hose failure can result in rapid coolant loss and engine overheating.
Installation Notes
- Inspect the thermostat housing connection, heat-exchanger inlet fitting, and hose clamps 961670 when replacing 859800
- Ensure the hose is fully seated on both connections before tightening clamps
- Route the hose without kinks and away from sharp edges or hot components
- After installation, refill and bleed the cooling system per the applicable Volvo Penta procedure
- Inspect all hose connections for leakage as the engine reaches operating temperature
Technical FAQ
What did 859800 replace?
859800 supersedes the earlier Volvo Penta hose 859808. If you have been ordering 859808 for your MD22-family engine, 859800 is the current OEM replacement.
Can I use a generic coolant hose instead?
Not recommended. 859800 is a specific molded hose with a defined routing path between the thermostat housing and heat exchanger. The MD22-family cooling system uses several short hoses and tubes in close proximity — matching the OEM part ensures correct fitment, routing, and sealing on both connection points.
How do I confirm this is the right hose for my engine?
Check the engine model and serial number against the Volvo Penta cooling system parts diagram for your specific variant. The MD22/TMD22/TAMD22 family used different hose arrangements across production runs and model variants, so diagram confirmation is the most reliable method.
Parts Desk Insights
This hose is most often needed during thermostat or heat-exchanger service on MD22-family engines — it is the connection between those two components and is frequently deteriorated by the time either is being serviced. The most common issue is customers ordering by engine model alone without checking the cooling system diagram, which can result in the wrong hose when the routing differs between variants. Worth having clamps 961670 on hand at the same time — if the hose is being replaced, the clamps should come with it. Also: if 859808 is requested, advise the customer that 859800 is the current OEM replacement.
Related Parts
- Volvo Penta OEM Heat Exchanger O-Ring 3580818 — heat exchanger sealing component
- Volvo Penta Heat Exchanger / Aftercooler O-Ring 3581070 | D2 D3 Diesel
- Volvo Penta Thermostat Gasket 3584299 – D3 Diesel — thermostat assembly sealing
- Volvo Penta Thermostat Cooling O-Ring 3586514
- Volvo Penta Coolant Pump 3803516 — closed-circuit coolant pump, special order
- Volvo Penta Aftercooler Gasket 859196 – AQAD40 / TAMD40
Shipping information
In-stock and OEM parts: ship same or next business day.
Supplier-stock items are usually ready for pickup or shipping within 24 hours of ordering.
Special-order timing may vary.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.