ISO 4081:2016

INTERNATIONAL ISO
STANDARD 4081
Fourth edition
2016-10-15
Rubber hoses and tubing for cooling
systems for internal-combustion
engines — Specification
Tubes et tuyaux en caoutchouc pour systèmes de refroidissement pour
moteurs à combustion interne — Spécifications
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
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ii © ISO 2016 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3  Classification . 2
4 Size and tolerances . 2
5 Performance requirements for hose and tubing . 2
6 Frequency of testing . 5
7 Marking . 6
Annex A (normative) Dilation test . 7
Annex B (normative) Resistance to surface contamination by engine oil .8
Annex C (normative) Pressure, vibration and temperature test . 9
Annex D (informative) Example of how a non-standard type of hose or tubing could be
specified by an original equipment manufacturer (OEM) using a matrix .11
Annex E (normative) Type test .12
Annex F (normative) Routine test .13
Annex G (informative) Production acceptance test .14
Bibliography .15
Foreword
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electrotechnical standardization.
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described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/TC 45, Rubber and rubber products, Subcommittee
SC 1, Rubber and plastics hoses and hose assemblies.
This fourth edition cancels and replaces the third edition (ISO 4081:2010), of which it constitutes a
minor revision. The following change has been made:
— Clause 2 has been updated, where ISO 1746 and ISO 4672 have been deleted and replaced by
ISO 10619-1 and ISO 10619-2, respectively.
iv © ISO 2016 – All rights reserved

INTERNATIONAL STANDARD ISO 4081:2016(E)
Rubber hoses and tubing for cooling systems for internal-
combustion engines — Specification
WARNING — Persons using this International Standard should be familiar with normal
laboratory practice. This International Standard does not purport to address all of the
safety problems, if any, associated with its use. It is the responsibility of the user to establish
appropriate safety and health practices and to ensure compliance with any national regulatory
conditions.
1 Scope
This International Standard specifies the requirements for straight or pre-formed rubber hoses and
tubing for use in pressurized or unpressurized cooling circuits containing 1,2-ethanediol-based
coolants in internal-combustion engines for vehicles with an unladen mass (as defined in ISO 1176)
of 3,5 t or less. In addition, this specification may also be applied as a classification system to enable
original equipment manufacturers (OEMs) to detail a “line call-out” of tests for specific applications
where these are not covered by the main types specified (see example in Annex D). In this case, the hose
or tubing would not carry any marking showing this ISO specification number but may detail the OEM’s
own identification markings as shown on their part drawings.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 188, Rubber, vulcanized or thermoplastic — Accelerated ageing and heat resistance tests
ISO 1307, Rubber and plastics hoses — Hose sizes, minimum and maximum inside diameters, and tolerances
on cut-to-length hoses
ISO 1402, Rubber and plastics hoses and hose assemblies — Hydrostatic testing
ISO 1629, Rubber and latices — Nomenclature
ISO 1817, Rubber, vulcanized or thermoplastic — Determination of the effect of liquids
ISO 6162-1, Hydraulic fluid power — Flange connections with split or one-piece flange clamps and metric or
inch screws — Part 1: Flange connectors, ports and mounting surfaces for use at pressures of 3,5 MPa (35
bar) to 35 MPa (350 bar), DN 13 to DN 127
ISO 7233, Rubber and plastics hoses and hose assemblies — Determination of resistance to vacuum
ISO 7326:2016, Rubber and plastics hoses — Assessment of ozone resistance under static conditions
ISO 8033, Rubber and plastics hoses — Determination of adhesion between components
ISO 10619-1:2011, Rubber and plastics hoses and tubing — Measurement of flexibility and stiffness —
Part 1: Bending tests at ambient temperature
ISO 10619-2:2011, Rubber and plastics hoses and tubing — Measurement of flexibility and stiffness —
Part 2: Bending tests at sub-ambient temperatures
ISO 23529, Rubber — General procedures for preparing and conditioning test pieces for physical test methods
SAE J20:2006, Coolant system hoses
SAE J1638, Compression set of hoses or solid discs
SAE J1684:2005, Test method for evaluating the electrochemical resistance of coolant system hoses and
materials
3  Classification
The product shall consist of rubber materials with or without an integral reinforcement which may
or may not be pre-formed before final vulcanization. The hoses and tubing may be branched, in which
case the method of attachment of the branch shall be such that the integrity of the hose is maintained
when it is tested to this International Standard. This International Standard does not cover methods of
attachment to mounting spigots.
Four types of hose and tubing for specific applications are specified as follows:
— Type 1 = Tubing and hoses for ambient operating temperatures from −40 °C to +100 °C;
— Type 2 = Tubing and hoses for ambient operating temperatures from −40 °C to +125 °C;
— Type 3 = Tubing and hoses for ambient operating temperatures from −40 °C to +150 °C;
— Type 4 = Tubing and hoses for ambient operating temperatures from −40 °C to +175 °C.
Wherever economically and technically possible, hoses and tubing shall use in their construction
materials that are capable of being recycled. Also, wherever economically and technically possible,
hoses and tubing shall use in their construction materials that contain post-consumer or post-industrial
recyclates.
4 Size and tolerances
Bore sizes and tolerances shall be in accordance with ISO 1307. Wall thicknesses shall be sufficient to
meet the requirements of this International Standard.
5 Performance requirements for hose and tubing
Tests shall be selected from the following list for each application of hose or tubing, based on the
performance requirements of the finished product. Type tests (as defined in Clause 6) for each hose or
tubing type are given in Annex E.
a) Burst pressure
When determined in accordance with ISO 1402 at standard laboratory temperature as specified in
ISO 23529, the minimum burst pressure shall be:

Tubing: 0,2 MPa (2 bar) for all diameters
Hose: 1,2 MPa (12 bar) for diameters up to and including 18 mm
0,9 MPa (9 bar) for diameters >18 mm up to, and including, 35 mm
0,5 MPa (5 bar) for diameters >35 mm
b) Adhesion (for all constructions with two or more bonded layers only)
When determined by the appropriate procedure of ISO 8033, the adhesion between each pair of
bonded layers shall not be less than 1,8 kN/m for unaged hoses and not less than 1,3 kN/m for
2 © ISO 2016 – All rights reserved

hoses aged as specified in test i), immersed in oil as specified in test k) and fatigued by vibration as
specified in test l).
c) Low-temperature flexibility
— For hoses and tubing of 25 mm inside diameter and below, with a minimum free straight-length
section of 300 mm
When cooled to −40 °C ±2 °C for 5 h ±0,5 h and tested in accordance with method B of
ISO 10619-2:2011, the hose or tubing shall not exhibit any cracking when examined
under 2× magnification after bending within 4 s arou
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