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Thread: Understanding how your Thermo cooling system works Reply to Thread
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Topic Review (Newest First)
06-07-2019 09:44 AM
TheMtnLord Awesome write up! Just had my radiator crack on me on Monday...
05-25-2019 12:04 AM
cudaboy yeah deep sockets work too and the sizes where on the first page. I also have a lot of tools and sockets sizes in my oddball and large tool thread that is also in the red F.A.Q. sticky.
05-24-2019 07:29 PM
richrd0001 On my '89 Prelude SI the part you've labeled WT5009 (9) is where 36426 is in your photo and 36426 is where WT5009 is in your photo.



The WT5009 part has about a 15mm threaded base and 36426 has about a 10mm threaded base. WT5009 needs a 22mm wrench, the other 19mm.
08-08-2018 05:28 AM
Shivanibhutani22 Wow, great
08-06-2018 05:38 PM
Blainethemono Shell out $130!!???

www.row52.com ask a Salvage yard Expert for an "experienced" fan timer. Mine was $30 for my Accord shipped!!

Another thing that was missed in this write up. Make sure the Radiator isnt plugged up & temp sensor drains water fully and not just trickles out. My Accord was plugged up and the Sensor was not getting enough water to trigger the senor to turn the fans on. Once I replaced the radiator and Fan timer, all was good with the world....
08-06-2018 12:47 AM
cudaboy correct fan timer pic located. I am to busy right now to upload a pic. Here is an existing thread in the f.a.q. with a fan timer pic. The only difference is all them I have seen are black. Guessman said it was an 88s carbed so I guess that is why it is brown. 88 they did different things on some of the 3rd gen ludes.

here ya go:

Ok I couldn't copy and paste the pic from the thread. I don't know what changed. I use to be able to do that. It is the 3rd pic down from factory diagram 16-14 pretty close to the top of post 10 by guessman. It a brown box in this picture bolted to the cowl side panel/ kick panel area with its connector at the bottom. All of them I have seen are just like this picture with a black plastic box. Regardless it will be in same location and same shape. Here is the link:

https://www.preludepower.com/forums/...d.php?t=275353
10-10-2016 09:21 PM
88SE Lude lol ... got this new small keyboard ... not easy when you type with your elbows
10-10-2016 07:16 PM
cudaboy old climate that's a new one. hehe
10-10-2016 07:12 PM
88SE Lude They are for different climates. It's as important to not overcool as it is to cool.

The 82C variety will work fine for you unless in a old climate.
10-10-2016 11:17 AM
Honca i had one question regarding the thermostat:

Why are there 2 rated values 82C (180F) and 88C(190F) listed for the same car. How do i tell which one is installed in the car without disassembly. (i want to order the replacement first)

the manual says starts to open 82C +-2 (180F) ,service limit 86-90C

i'll be using the car mostly on summer so the 82C version should be fine, right?
09-12-2016 05:10 AM
cudaboy thread with my ebay links:

https://www.preludepower.com/forums/s...d.php?t=442801
09-12-2016 03:19 AM
Nigeltay
Quote:
Originally Posted by cudaboy View Post
The fan timer I repair but not sure you want to pay shipping. let me know if you do. I use to have spares that I got at the junkyard but they have all been rebuilt and sold for couple years now. They are getting harder to find. If you do want to send me one I can tell you what years and cars that have them.

I have never worked on a carbed lude but the thermovalve switches just allow vacuum to a part in the system as far as I know and once they warm up they shut it off. Or the direct opposite of that. I think it just works to aid the choke or in place of the choke if we don't have one. Like I said never worked on a carbed lude. Those switches are hard to find new. Due to engine heat the plastic vacuum tips or the entire plastic end breaks off. Since I did get a thermostat housing aka water neck that had one I can tell you that you will wan't a switch with 3/8" BPST thread. BPST STANDS FOR BRITTISH PIPE STANDARD TAPERED THREAD PITCH. Very similar to usdm npt thread but slight difference in thread count per inch. usdm npt stands for national pipe tapered. You can screw npt into bpst hole but you sort of ruin the threads. Kind of a one time deal. I did it with a npt 3/8" reducer brass bung for my 1/8" npt electronic water temp sending unit and it doesn't leak. I put teflon tape on the threads I am pretty sure. I have other water necks that I could drill and tap if this one ever goes bad.
i just double check the wires and connectors, now the connector for the switch below the rad cant seem to be jumped with paper clips. i plugged back the fan motor to the connector, and try to jump the switch connector with a paper clip but the fan didnt turn on. while researching, i remembered i came across a thread where a member shared an ebay link for the brand new connector but i cant seem to find it now..

i'll take note of your advice regarding the thread type and sizes if the vacuum switch ever snaps off. i dont think the shipping would be cheap as i live in singapore but if i'm desperate in the future, i know who to look for!

oh, and i also checked all the fuses, they're still good. i guess its just the wiring problem><
09-11-2016 11:42 PM
cudaboy The fan timer I repair but not sure you want to pay shipping. let me know if you do. I use to have spares that I got at the junkyard but they have all been rebuilt and sold for couple years now. They are getting harder to find. If you do want to send me one I can tell you what years and cars that have them.

I have never worked on a carbed lude but the thermovalve switches just allow vacuum to a part in the system as far as I know and once they warm up they shut it off. Or the direct opposite of that. I think it just works to aid the choke or in place of the choke if we don't have one. Like I said never worked on a carbed lude. Those switches are hard to find new. Due to engine heat the plastic vacuum tips or the entire plastic end breaks off. Since I did get a thermostat housing aka water neck that had one I can tell you that you will wan't a switch with 3/8" BPST thread. BPST STANDS FOR BRITTISH PIPE STANDARD TAPERED THREAD PITCH. Very similar to usdm npt thread but slight difference in thread count per inch. usdm npt stands for national pipe tapered. You can screw npt into bpst hole but you sort of ruin the threads. Kind of a one time deal. I did it with a npt 3/8" reducer brass bung for my 1/8" npt electronic water temp sending unit and it doesn't leak. I put teflon tape on the threads I am pretty sure. I have other water necks that I could drill and tap if this one ever goes bad.
09-11-2016 11:22 PM
Nigeltay
Quote:
Originally Posted by cudaboy View Post
yeah as you stated the small single wire sending unit is just for the gauge. Nothing else. The lower radiator switch is for the fan. This switch is set with in 5 degrees of 90 celsius on the usdm fuel injected but I would have to look to see if it was the same for carbed. If you had an infrared temperature gun you could point it at the lower radiator by the switch when it is kicking on. Or take the switch out and test it on a cooktop in a can of water. The shop manual shows how to do this or if not it is the same for the thermostat. Which is in the manual as a test on a cook top.

On the thermovalve vacuum switch are you able to find a replacement. I was going through some of my old private messages and recent ebay searches I think some would work. They are only two port but you could run vacuum "T"'s on the out going port if needed. The 88 fuel injected had some that had this thermoswitch for vacuum. I know on some of the Canadian models there was a separate sensor on the fire wall behind the engine. I have no idea if I have a pic of that or could even find it onhere. I might look tomorrow through my computer files.

It might be a loose connection in the wiring to the radiator fan motor if bypassing the stock wiring harness to get the lude home kept it on.
thank you for the helpful reply! however i tested my thermoswitch (the one located at the bottom of the rad) before i installed it to confirm it was working perfectly. it was a new beckarnley part from rockauto.

could it be a problem with the radiator fan timer? as for all the years i've been driving the car, the fan NEVER kicks on after i pull the key out of ignition. i saw some threads where a few members experience problems with the fan timer causing the cooling fan to kick on at random times even when the engine is completely cool. i would want to wire it to a turbo timer or something like that if its possible so i can control how long i want my fans to be on after key off.

also, how does the themovalve vacuum switch work and what is it's purpose? i can see there is another identical switch like that located on my intake manifold. it's like $38usd excluding shipping on rockauto.

right now still running with the fan wired directly to the battery, kinda lost on how to identify the fault and get everything working fine.
09-10-2016 01:28 AM
cudaboy yeah as you stated the small single wire sending unit is just for the gauge. Nothing else. The lower radiator switch is for the fan. This switch is set with in 5 degrees of 90 celsius on the usdm fuel injected but I would have to look to see if it was the same for carbed. If you had an infrared temperature gun you could point it at the lower radiator by the switch when it is kicking on. Or take the switch out and test it on a cooktop in a can of water. The shop manual shows how to do this or if not it is the same for the thermostat. Which is in the manual as a test on a cook top.

On the thermovalve vacuum switch are you able to find a replacement. I was going through some of my old private messages and recent ebay searches I think some would work. They are only two port but you could run vacuum "T"'s on the out going port if needed. The 88 fuel injected had some that had this thermoswitch for vacuum. I know on some of the Canadian models there was a separate sensor on the fire wall behind the engine. I have no idea if I have a pic of that or could even find it onhere. I might look tomorrow through my computer files.

It might be a loose connection in the wiring to the radiator fan motor if bypassing the stock wiring harness to get the lude home kept it on.
09-10-2016 01:04 AM
Nigeltay
B20a4 cooling fan problem

hey everyone i need some help here.
first of all sorry to bring back such an old thread ,i tried to search for a solution to my problem but to no avail..

so here's what's going on, my cooling fan is only working sometimes.
i know its supposed to on and off intermittently depending on the coolant temp but in my case its really working for a day and totally stops the next.

what i've done so far is getting a new temp sensor on the thermo housing (the small one for the gauge), checked the relay, checked all fuses, checked the fan motor, and i jumped the connector for the switch at the bottom of the radiator (and everything was good). so i replaced that switch at the bottom of the rad with a new one, and the cooling fan was working perfectly again. i let it run for a full hour while monitoring the cooling fan and it was turning on and off just like how it should be.

The next day i took it for a drive and noticed my temp gauge was at the 3 quarter mark, so i pulled over, popped the bonnet and sure enough the cooling fan wasnt working again... however the condenser fan was on even though my ac is off, but it turned of after 30 seconds or so. when i turn the ac on, only the condenser fan is running when both should be operating.

i wired the cooling fan directly to my battery taking the risk of burning out the fan motor so i could drive home safely.

just so you guys know, my engine is the carbed model without the emissions crap and i noticed that the sensors located on the thermo housing are different from most of the writeups. for those dohc fi models, you have the 2 switches which my model does not have. i only see the small temp sensor for the gauge and a vacuum switch with 2 hoses connected to the intake manifold area.

Really hope there are some carbed luders out there that could help me with this issue as i do not want to send the car to a workshop unnecessarily!
thanks!
06-06-2015 07:22 AM
stretchjax Thank you so much for this My 89 si had a toggle switch under the dash to the condensor fan and radiator fan didnt work at all this thread was my roadmap to restoring it back to the sensors where it belongs
12-23-2014 05:30 PM
cudaboy well I will see about getting the pics up it will take awhile. I should have pics with the sockets needed in my oddball and large tool thread in the f.a.q.
12-23-2014 05:26 PM
cudaboy not sure what you said but if your throwing an engine temp code at the ecu then check connection and replace the ecu temp sensor at the water neck. There is a pic first page by me with part numbers. It is the one with the smallest depth of socket conctact area. The other has a thick body because it is not a sensor and is the condenser fan switch. If you have replaced the condenser fan switch at water neck and lower radiator switch and checked or replaced the two fan fuses/relays and wiring. I rebuild the fan timers but I won't be able to get to it for awhile. The fan fuses are or should be in the underhood fuse box. I know the relays are there.
12-23-2014 04:36 PM
bgdg1141b Also it'ssstayingIin limp mode and ichecked the codes on the ecu and it's temp and cooling
12-23-2014 04:34 PM
bgdg1141b I read through these posts and I'mhaving a problem with my fans the fan works but it doesn't cut on with the timers I've checked the connectors with a tester and they aren' getting power that hooks to the radiator my fuses are good also any advice
11-15-2013 09:23 PM
pjlght
Check the fuses first! Including the rear defrost.

I read through most of your post and even used a couple of your pictures. Great work. Thanks! BUT!!! I was having problems with my A/C not working, the lights on my climate controls not working as well as the climate controls themselves and my fans not coming on (and didn't realize it) that cause my 89 to start over heating in stop and go traffic. After checking my relay operation and manually operating my fans and other such useless actions, I still had no problem confirmed. Yeeeah... So it turns out my rear defroster fuse had failed. As soon as I replaced it EVERYTHING was functioning again!! A long running saying in the automotive repair field is to always start with the easiest possibility first. I wish I had known/realized when I got started, it would have save me a lot of time. Ooops. I'm new to these.
08-17-2012 07:16 PM
redloudlude Wow thanks so much that helps
08-17-2012 05:49 PM
cudaboy I have a guy that will rebuild fan timers. He hasn't done one before but has done other similar parts. He is from an nsx forum. Pretty sure I have posted his email before. Cost is just $25 to fix it and get it back to you. He said he would replace any capacitors and check it over. I will look in my outlook express. Here ya go!

[email protected]
08-17-2012 04:19 PM
ReyKe Look if push comes to shove you can always bypass the factory black box, just set it up on a relay, that's all the fan switch does when it hits a certain temperature it grounds out and the box reads that ground and turns the fans on.
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