joejoe

1984 auto (us) has develped a sever overheating problem. Symptoms are: upper hose hot lower hose cold, radiator cold. Tried removing thermostat and problem still persists. Believed w/p impeller was spinning on shaft so new one was bought. After removing w/p shaft and impeller seem perfect, no wear and impeller is tight on shaft. Pulled spark plugs thinking perhaps blown head gasket but plugs looked uniformed and no apparent coolant contamination. There has also been no coolant loss from system.

This heating problem started during an hour drive (about 50 miles) when noticed temp guage was near upper red mark. Warning light did not come on but temp was higher than normal (normal temp is first hash mark) A few days later driving around town warning light came on and when car cooled pulled thermostat to see if that made a difference. There was no change in overheating problem leading to belief there was no flow and w/p gone south. This brings us to where we are now.

This is a friends car and we are really stuck on what to do next. Put new w/p on and go? Use old w/p? Is there anything else we need to check? Really stimied here and any help would be greatly appreciated.

DougM

check the coolant cap. After chasing every possible problem on my car, it ended up being a bad cap.

Bill Ball

Removing the Tstat is exactly the wrong approach. Unlike a lot of american cars, the 928 Tstat is essential for the cooling system to work. In the 928, the Tstat does NOT open the path to the radiator. Rather, it CLOSES a radiator bypass in the water bridge that directs coolant back through the block when cold. Test the Tstat by putting it in hot water and see if it moves. It should completely close by 195 degrees. Then, if OK, put it back in. If bad, then that's your problem. Replace it.

Also, make sure the large o-ring is on the OUTSIDE, not under the Tstat.

Also, there is a rubber coated metal seal in the water bridge that the Tstat closes against. It can be very hard to see when it gets worn and corroded, so I've shown some pictures of it below. It must be pried up and yanked out. A problem with the seal is not enough to cause much overheating, but it should be replaced if it hasn't been already.

You were right to suspect the WP impeller, particularly if it is plastic. I'd make double-sure it is tight.

SeanR

Did you say you replaced the impeller on the water pump and not didn't replace the water pump?

Mrmerlin

I wasnt clear on if you already installed a new water pump .

when testing the thermostat you need an IR gun to know what the temps are that it is opening at.

Same goes for the coolant,
you need numbers of how hot things are getting,
remove the temp sensor and see if there is anything clogging the port below it.

To fix a coolant system replace the heater control valve and short hose,
the thermostat and the seal behind it,
the coolant bottle cap,
The waterpump with a new Laso


Has there been any leak sealant put into the system?
If so ,it may have plugged up the headgasket holes and thus reduce the cooling efficiency of the system.

joejoe

Thanks for replies. Sean the waterpump that was removed is like new, is a laso pump with metal impeller. As of right now car is apart, new pump is laso also, but not installed yet. My friend is on a budjet and was wondering if should use the new pump or old. Bill, I explained this (need for t/stat) for operation of system, but I forgot to look at metal seal, After all was apart he mentioned that he had removed t/stat (grrrrr). I have to check operation os stat tomorrow.

After I took Mark home I did a bit more exploring and found the coolant overflow nipple broken, no wiring to low coolant level sensor and a mysterious vacuum hose with a bolt stuck in it (I believe it goes to charcoal canister)

Forgot to mention in beginning post that there is pressure on both upper and lower hoses. The cap is a stant with pressure relief handle. Will check on all the suggestions tomorrow, and again the help is greatly appreciated.

Bill Ball

If the old WP was a metal impeller, you would know if it was loose - it would make a racket. Even though the cold radiator is consistent with a bad impeller, it seems unlikely based on your examination of the WP. The only other things that can stop flow are a plugged radiator, also unlikely, or a bad thermostat. If the thermostat is stuck in the cold position and fails to close off the bypass, that would account for the overheating. So, while you are replacing the thermostat, renew the seal and make sure the o-ring is on the outside (in front of) the thermostat.

You say there is a broken nipple on the overflow. Obviously losing coolant will cause overheating. The hoses will still be turgid from steam pressure.

If the cap were bad, coolant still circulates, so the radiator should still be hot. The system is not as efficient and coolant will boil off, particularly when you shutdown the car, but as long as the coolant level is good, a bad or missing cap does not cause much of a problem, as long as the engine is running. Once the engine is stopped and coolant stops flowing, the heat coming out of the motor quickly boils the coolant and you can get a gusher.

That plugged hose is part of the gas vapor recovery. If it's the section that leads down under the intake toward the throttle, leave it plugged. If it is open and not connected to the rest of the system, it becomes a major vacuum leak.

joejoe

Update on car, it is back on the road (for the time being) As it turned out it was the thermostat. I it just flat would not function. Luckily I happened to have one here and car went together with only a few mishaps.

As my friend was putting pieces back on I kept reminding him to check and double check everything, this kindda irritated him a bit and he really let me know that he knew what he was doing so I just shut up. As he was about to put the last accessory belt on I really felt sorry for him and again piped up 'is everything good?, take a close look at your work'. He came to the realisation then that he had forgotten to put the center cover on. (This is what I was about to tell him when he got snippy)

Eventually the front was done and fluid added. Car start upeasily and as temp rose could tell when themo opened. Flow across radiator was good and all seemed well. Turned car off checke bay and lifted car again. Damit coolant leaking from rear engine area! THEN I am informed that the heater valve has been replaced with something from a chevy or some such piece of crap. (I really didn't care) Anyway, I told him he could leave car again and get corroct parts but he wanted to drive (I do understand that part) so valve was bypassed and off he went.

Thank you all for the advise again. This was quite the episode the time around and a few things got hurt. First was a craftsman torque wrench (it jsut broke, no ratcheting either way), and the other was driver side cover got a bit melted (my friend laid the 500watt halogen light on it while I was looking for spare heater valve)

On a strange side note about 5 years ago I looked at this car thinking of buying it. Upon closer (not really terribley close) inspection it was obvious that the car needed way more work than I wanted to do at the time (bad oil leaks,major service needed, badly wired electric fan, mismatched hood not quite sitting right, and then the interior. All this for only 6k! I told the owner I would think about it and clenched my butt cheeks and walked quickly away. Since that time I have done most of the work needed on the car lol. It will be interesting to see if my friend gets the parts still needed for his car: correct rad cap, rubber seal Bill mentioned, as well as a few other things I mentioned to him. Been a long day and I still have to finish clean up tomorrow. Many thanks again.

Mrmerlin

To fix a coolant system replace
the heater control valve and short hose,
the thermostat and the seal behind it,
the coolant bottle cap,
The waterpump with a new Laso

Bill Ball

I think you'll be seeing this car for further repairs very soon.

danglerb

Might have been a lot less work for you if you bought it instead of your friend.

vernon

My 1984 928 was runing very hot also the seal in back of the thermostat was shot it look like the one that you have.I put a new one in an a new thermostat also a new cap an new coolant. for the last two years it been runing very cool an not over heated one time. Also I put in the large o-ring that is on the OUTSIDE of the thermostat. Vernon/

outbackgeorgia

Take that Craftsman wrench back to Sears for a new one, lifetime warranty!
Dave

Bilal928S4

I think if you read the fine print they do not warranty the torque wrenches for life, it's for 6 months or something. Also the regular rachet wrenches are either rebuilt or exchanged for a rebuilt used one.

joejoe

Fine print is 90 day exchange, up to 1 year send away and get another. Bought a Husky and it is lifetime waranty.