From: Dr. Bob [dr.bobf@worldnet.att.net] Sent: Tuesday, July 25, 2000 10:19 AM To: 928 Subject: [928] re: Thermostat Steve Lewis responded to a previous post: >>I have >>drilled the thermo housing with bypass holes( as recommended by several >>highly experienced Porsche mechanics > >If I am not mistaken, the 928 thermostat performs in the opposite manner to >"normal" thermostats. It closes when it heats up and lets the engine water >go through the radiator. When it is open, some water bypasses the >radiator and recircs through the engine. I think your highly experienced >Porsche mechanics need some more experience and you need a new >thermostat again. I posted a couple messages to the list on the thermostat subject in the last year, and one of them pointed out how the operation of the thermostat is different from what one typically sees in automobiles these days. DR mailed me off-list back then (I've reduced the dosage since then, Dave ;-)), letting me know that the way I described the operation wasn't exactly accurate. I'll try again, and maybe some of this will clear up the confusion. The original response way back then was to somebody considering taking the thermostat out to increase water flow, so the description then was very targeted. The thermostat in the 928 does two things. If you look inside the water manifold where the thermostat sits, you'll see passages that connect to both radiator hoses and the passages in the block. In normal operation, the thermostat is open to the radiator, and the bypass between the discharge and inlet ports is blocked closed. The thermostat flange that the sealing o-ring wraps around could be drilled to allow coolant flow to the radiator even when the engine is cold, and that sounds like what was done here. Going to the cold condition, the thermostat normally blocks flow through the radiator, and also allows coolant to bypass between the discharge and inlet ports on the block. This bypass flow eliminates those local hot spots in the block, promoting a nice even warm-up of the block from cold. As the coolant temp comes up, the bypass closes, the radiator outlet opens, and coolant is directed through the radiator. Looking at that function, it would seem that drilling the thermostat would extend the engine's warm-up time if the holes are very large. Many cars have small holes drilled in that front flange. Primary reason is to allow gas or air bubbles to pass through. My Explorer, for instance, has a very specific instruction to make sure the thermostat vent hole is at the top when installed. If you don't follow that rule, you risk having a gas or steam bubble in the top of the housing where the temp sender is located. With the bubble, gauge readings are false and slow. It's pretty sucky too, because if you lose coolant in that car, you lose accurate gauge reading almost immediately. Anyway, I suppose there might be a case for drilling a vent hole in the 928 thermostat, I just haven't seen the need yet. The system burp procedure following a coolant change is pretty interesting, but once done there doesn't seem to be any problem with bubbles in the water manifold. I'm open to discussion/criticism of this subject. I just don't want to have my previous partially-correct description propogated as complete. I apologise for causing the confusion. Best regards, dr bob Jim McCown wrote: > Hi All, > I am obviously missing something here. I admit to being a novice to the 928 > but it sounds like the 928 thermostat works just like any other car. When > cold it prevents water from the radiator from circulating through the engine > and once the water reaches the appropriate temperature it opens to allow > water from the radiator to circulate through the engine. > > Why can't you run a 928 without a thermostat? It would seem that if you > removed the thermostat that water from the radiator would be circulating > through the engine all the time. What is it about the 928 that you can't do > just that very thing?? > Thanks in advance for explaining this to me! > > Jim McCown > 1984 928S A/T From: Wally Plumley [wplumley@avana.net] Sent: Monday, July 24, 2000 5:48 PM To: 928 Subject: [928] Re: thermostat At 02:16 PM 7/24/00 +0000, eds928gt@freewwweb.com wrote: >Not exactly. When the engine temp is lower than the temp setting to open >the thermostat, it is CLOSED. While it is closed the water in the engine >is recirculated. When the temp reaches that needed for opening the >themostat, it OPENS and allows cooled radiator water to circulate through >the engine. When the thermostat is fully open, the section that allows >water to recirculate in the engine gets closed off. > >Caution. Never run a 928 without a thermostat. This leads to an interesting problem. When the thermostat on most other cars fails on the road, causing overheating, you can usually just remove the thermostat and continue on your way. Doesn't work on a 928 - so what do you do? One of the 928 Owners Club members was faced with exactly that problem on the way to Wichita. Luckily, he had read on the list that he couldn't just remove the thermostat, so he didn't make that mistake. What he did was to take the thermostat out and place an 11 mm socket between the operating disk of the thermostat and the engine housing. When he reinserted (carefully!) the thermostat, the socket pushed it to the open position - Problem Solved!! I think that it was Fred Clark, but I may be wrong about that. Darned clever, in any case. Wally From: DPW928@aol.com Sent: Tuesday, July 25, 2000 8:37 PM To: 928 Subject: [928] Re: thermostat Jim, If you look at the 928 thermostat you will notice an extra plate on the bottom. When the engine is cold, this plate is up and allows water to circulate throughout the block. This reduces hot spots during warm ups. As the valve to the radiator opens, the plate closes the recirculation through the block. If you run without a thermostat, the water will take the path of least resistance and just circulate in the block with very little going through the radiator. Dennis From: Gary Casey [glcasey@gte.net] Sent: Tuesday, July 25, 2000 11:02 PM To: 928 Subject: [928] Re: thermostat I think the explanation is that these thermostats are actually three-way valves. They take the outlet from the engine and direct it EITHER to the radiator or back to the engine. In that way the flow rate through the engine is unimpeded when cold. One reason to do this is to keep the engine at a uniform temperature as it heats up. Another is to make sure that the thermostat sees the true engine temperature. Take the thermostat out and the coolant can flow equally well to the radiator or to the engine. The engine is the shorter path so most of it goes there and very little goes through the radiator causing sure overheating. Many German and some US engines are made this way. Make sense?