Cooling system plumbing 1986 vs 1991 and newer Accords
My son called the other day and was telling me about changing the thermostat
in his 1991 Accord. He said this involved removing the lower radiator hose where it connected to the thermostat housing. I knew that on my 1986 Accord, and on every other vehicle I have worked on that the thermostat is at the upper radiator hose, restricting the flow back to the radiator. This is the same as the schematic shown in the link from "how stuff works" below. http://www.howstuffworks.com/cooling-system.htm I thought he was either mistaken or something was connected up wrong, but I looked in the 1991 service manual, and sure enough, the hose connections are the reverse of what I expected. I confirmed this by looking under the hood of a friend's 1991. This plumbing arrangement doesn't make sense to me. Surely, the water is still being pumped from the radiator bottom hose, but now flow is being restricted into the engine. It seems that this could result in cavitation or running the water pump dry. Is there an explanation as to why this would be a better than the old plumbing? TIA John |
Re: Cooling system plumbing 1986 vs 1991 and newer Accords
"JP" <xjj_potterx@xhotmailx.com> wrote in
news:0dednTJ02uJp-vPUnZ2dnUVZ_vKdnZ2d@earthlink.com: > My son called the other day and was telling me about changing the > thermostat in his 1991 Accord. He said this involved removing the > lower radiator hose where it connected to the thermostat housing. I > knew that on my 1986 Accord, and on every other vehicle I have worked > on that the thermostat is at the upper radiator hose, restricting the > flow back to the radiator. This is the same as the schematic shown in > the link from "how stuff works" below. > > http://www.howstuffworks.com/cooling-system.htm > That's an "ode sku" cooling system! My dad's '70 Ford had such, as did all of my previous cars. > I thought he was either mistaken or something was connected up wrong, > but I looked in the 1991 service manual, and sure enough, the hose > connections are the reverse of what I expected. I confirmed this by > looking under the hood of a friend's 1991. I do believe 1990 was the first year for no carburetors in North America. > > This plumbing arrangement doesn't make sense to me. Surely, the water > is still being pumped from the radiator bottom hose, but now flow is > being restricted into the engine. It seems that this could result in > cavitation or running the water pump dry. You'd think so, but there are bypass hoses. So long as the thermostat remains closed, the bypass hoses bathe the bottom of the thermostat with a steady flow of coolant recirculated from and to the block, so as the block warms, the thermostat opens. Once fully open, the thermostat blocks the bypass hoses, so all the flow is past the thermostat bulb. The heater hoses also bypass the thermostat, by the way. > > Is there an explanation as to why this would be a better than the old > plumbing? > The change seems to have coincided with the advent of universal fuel injection and of more restrictive emissions controls. I'm guessing having the thermostat at the inlet end of the lower hose means better control over block temperature. Remember that excessive combustion temperatures result in excessive NO emissions. Better control over block temps mean less likelihood combustion temps will exceed 2,500F, which is NO territory. -- Tegger The Unofficial Honda/Acura FAQ www.tegger.com/hondafaq/ |
Re: Cooling system plumbing 1986 vs 1991 and newer Accords
On Wed, 14 Jan 2009 14:32:19 -0800, JP wrote:
> My son called the other day and was telling me about changing the > thermostat in his 1991 Accord. He said this involved removing the lower > radiator hose where it connected to the thermostat housing. I knew that > on my 1986 Accord, and on every other vehicle I have worked on that the > thermostat is at the upper radiator hose, restricting the flow back to > the radiator. This is the same as the schematic shown in the link from > "how stuff works" below. > > http://www.howstuffworks.com/cooling-system.htm > > I thought he was either mistaken or something was connected up wrong, > but I looked in the 1991 service manual, and sure enough, the hose > connections are the reverse of what I expected. I confirmed this by > looking under the hood of a friend's 1991. > > This plumbing arrangement doesn't make sense to me. Surely, the water > is still being pumped from the radiator bottom hose, but now flow is > being restricted into the engine. It seems that this could result in > cavitation or running the water pump dry. > > Is there an explanation as to why this would be a better than the old > plumbing? > > TIA > > John tegger got it right. in the mean time, ask yourself whether it matters which end of a pipe you put the faucet. |
Re: Cooling system plumbing 1986 vs 1991 and newer Accords
"jim beam" <spamvortex@bad.example.net> wrote in message
news:XsTbl.1776$ye3.603@fe12.news.easynews.com... > On Wed, 14 Jan 2009 14:32:19 -0800, JP wrote: > >> My son called the other day and was telling me about changing the >> thermostat in his 1991 Accord. He said this involved removing the lower >> radiator hose where it connected to the thermostat housing. I knew that >> on my 1986 Accord, and on every other vehicle I have worked on that the >> thermostat is at the upper radiator hose, restricting the flow back to >> the radiator. This is the same as the schematic shown in the link from >> "how stuff works" below. >> >> http://www.howstuffworks.com/cooling-system.htm >> >> I thought he was either mistaken or something was connected up wrong, >> but I looked in the 1991 service manual, and sure enough, the hose >> connections are the reverse of what I expected. I confirmed this by >> looking under the hood of a friend's 1991. >> >> This plumbing arrangement doesn't make sense to me. Surely, the water >> is still being pumped from the radiator bottom hose, but now flow is >> being restricted into the engine. It seems that this could result in >> cavitation or running the water pump dry. >> >> Is there an explanation as to why this would be a better than the old >> plumbing? >> >> TIA >> >> John > > tegger got it right. in the mean time, ask yourself whether it matters > which end of a pipe you put the faucet. > However, when the thermostat is in the upper hose it is responding to the cylinder head temperature, and the cylinder head is the main source of heat (especially when an aluminum head is mounted to a cast iron block). When mounted in the upper hose there is usually no flow past the thermostat, it just is bathed in the coolant of the hottest part of the engine. There has apparently been a design decision to heat the block rather than to leave it as part of the cooled fluid return path. I'd be curious to know why the change... possibly emission related or to manage the expansion of some or all the engine parts? Mike |
Re: Cooling system plumbing 1986 vs 1991 and newer Accords
On Fri, 16 Jan 2009 05:23:01 -0700, Michael Pardee wrote:
> "jim beam" <spamvortex@bad.example.net> wrote in message > news:XsTbl.1776$ye3.603@fe12.news.easynews.com... >> On Wed, 14 Jan 2009 14:32:19 -0800, JP wrote: >> >>> My son called the other day and was telling me about changing the >>> thermostat in his 1991 Accord. He said this involved removing the >>> lower radiator hose where it connected to the thermostat housing. I >>> knew that on my 1986 Accord, and on every other vehicle I have worked >>> on that the thermostat is at the upper radiator hose, restricting the >>> flow back to the radiator. This is the same as the schematic shown in >>> the link from "how stuff works" below. >>> >>> http://www.howstuffworks.com/cooling-system.htm >>> >>> I thought he was either mistaken or something was connected up wrong, >>> but I looked in the 1991 service manual, and sure enough, the hose >>> connections are the reverse of what I expected. I confirmed this by >>> looking under the hood of a friend's 1991. >>> >>> This plumbing arrangement doesn't make sense to me. Surely, the water >>> is still being pumped from the radiator bottom hose, but now flow is >>> being restricted into the engine. It seems that this could result in >>> cavitation or running the water pump dry. >>> >>> Is there an explanation as to why this would be a better than the old >>> plumbing? >>> >>> TIA >>> >>> John >> >> tegger got it right. in the mean time, ask yourself whether it matters >> which end of a pipe you put the faucet. >> >> > However, when the thermostat is in the upper hose it is responding to > the cylinder head temperature, and the cylinder head is the main source > of heat (especially when an aluminum head is mounted to a cast iron > block). except that there is no flow if the thermostat is closed, only convection. that leads to considerable local temperature differences within the head and block. keeping coolant actually flowing, as the honda design does, is a very smart solution. > When mounted in the upper hose there is usually no flow past the > thermostat, it just is bathed in the coolant of the hottest part of the > engine. > > There has apparently been a design decision to heat the block rather > than to leave it as part of the cooled fluid return path. it is part of a flow path, right from start-up. tegger exactly describes the flow mechanism - the thermostat is opened "from behind" and mixes hot with cold, not just waits for the whole assembly to heat before arbitrarily getting hot, then circulating cold coolant, etc. > I'd be curious > to know why the change... possibly emission related or to manage the > expansion of some or all the engine parts? > > Mike thermal consistency. honda engineers were not dumb with this design. not by any stretch. |
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