Thermostat: How To Tell If It's Dodgy

Post by **Ian** » Mon Dec 04, 2006 2:04 pm

Posted on behalf of Tony in Portsmouth:

"Dear nurse, i recently diagnosed my overheating problem via the archives as a blocked radiator, this was confirmed by the RAC apon rescue, i have had the rad recored and refitted and was very diligent in bleeding the system several times ,however it has not cured the original problem ,the waterpump seems fine (no leaks)the top hose does become warm after running up to temperature, however i now suspect it could be a faulty thermostat, i thinking of removing the thermostat and running the bongo to seee if this cures the problem before replacing with a new thermostat, is this a stupid idea, will this harm the engine in any way.....i seem to remember from my early car repair days that we often run older cars without a thermostat......any other ideas...."

Veg_Ian · Post by **Veg_Ian** » Mon Dec 04, 2006 2:14 pm

So what were the original symptoms?

A stat can fail in one of two ways:

1. Stuck in open position - symptoms, engine coolant takes a long time to reach optimum operating temperature.
2. Stuck in closed position - symptoms, engine coolant gets too hot, as coolant not allowed to flow, and overheats.

To check, remove stat and there should be a temp value stamped on it. Typically this might be 82 ie. 82 degrees centigrade. Place stat with a thermometer in a pan of water and bring to boil. If ok the stat will start to open at designated temp. If it doesn't replace.

mikeonb4c · Post by **mikeonb4c** » Thu Dec 07, 2006 12:58 am

I'm told its a bugger (and therefore costly in garage time) to access and change the thermostat on a Bongo - is this true. I ask because although my new Bongo seems to behave impeccably on the temperature front, I know it has not been serviced for 2 years and reckoned it might be good to get a Bongo expert to drain the system, give it a good backflush, refill with antifreeze and water. Because the thermostat is probably old too and given the hassle of draining and refilling a Bongo, I thought I might as well get a new thermostat put in. Oh and I'll get all hoses checked over and replaced if need be. Does all this sound like overkill?

moonshine · Post by **moonshine** » Thu Dec 07, 2006 9:12 am

Not at all, it seems like a wise move to me. Make sure you use someone who knows how to correctly bleed the system though, or you may be creating a problem you haven't got now.

Timnz · Post by **Timnz** » Thu Dec 07, 2006 9:20 am

I noticed I can drive 8km in stop start traffic with ambient temp of 20 c and the thermostat obviously wasn't opening when it should, I had to leave it idling for 5 mins after this before it would finally pop open, and there's a sudden temperature change from stone cold to hot at the bottom pipe.

It seemed to work fine if you do a long trip on the motorway.
I got the cambelt, drive belts and water pump done all at the same time(3.5 hours labour total), and replaced the water pump (only extra $130nz (40 something pounds) (another inaccessible item to replace in the future) and thermostat.
The thermostat very obviously opens at a lower temperature now, more gradually.

Bumbly1 · Post by **Bumbly1** » Thu Dec 07, 2006 11:21 am

Though the rad is now clear and the system has been bled, I think it could still have air in it. The rearmost heating matrix could still be blocked. The system would possiblt benefit from the addition of a flushing agent and then drained and refilled. I believe it is "difficult" get the air out of the rear heater thingys, caused my garage no end of heartache.

Hope all goes well for you.

Tom

mikeonb4c · Post by **mikeonb4c** » Thu Dec 07, 2006 12:45 pm

Thanks guys - a fantastic collection of tips. I'll assemble them into a spec and then get a quote from an experienced Bongo mechanic. The guy in Bury who does work for Manchester Campers seems to get v. high ratings - might ask him.

Best

Mike

Peg leg Pete · Post by **Peg leg Pete** » Sat Dec 09, 2006 9:34 pm

I managed to remove,check, replace with a new thermostat, I bought a cheap socket set from Argos, I am no mechanic, but managed to do it o.k. So a mechanic should do it easily when the bongo is on the ramp, I have no ramp and managed to work from above

mikeonb4c · Post by **mikeonb4c** » Tue Dec 12, 2006 12:20 am

Pete

This may sound a daft question. When you replaced your thermostat, did it involve draining and refilling the cooling system?

Also, where did you buy your Bongo thermostat from?

Thinking I might try the complete drain, backflush, thermostat change etc. myself!

Mike

Veg_Ian · Post by **Veg_Ian** » Tue Dec 12, 2006 9:08 am

This may sound a daft question. When you replaced your thermostat, did it involve draining and refilling the cooling system?

I would love to know how you would do it without draining