[captainOCD]

Since my blue car has been painted and aside from a few exterior cosmetic things that still need touched up and some more interior reupholstery, it really doesn't need much attention aside from driving right now. That combined with the pandemic has left me bored and I've started messing with the tan car now.

Since it's been a while since I've posted about it, I bought it in 2018. I did a timing belt/water pump job, replaced all fuel lines, put on new coolant hoses, made a new engine harness for it, serviced the trans, got the brakes to work, and repaired a host of wiring issues inside and in the engine bay. Currently it runs, goes, and stops. It is currently idling high, around 1200-1800rpm depending on the mood it's in.

After about 5 -10 minutes of running at idle it's showing the needle just under the orange mark on the dash. I've just shut it down at that point. So far I've replaced the inner thermostat seal, the new thermostat (that tested working) with another tested working original from the 84 parts car. I also flushed out the whole cooling system a couple months ago first with the garden hose then did the final flush with distilled water. Nothing seemed blocked including the radiator.
Initially the car was facing uphill and then had the front on ramps on top of that. I lowered it back down to the ground to see if that would help and it didn't. I've tried pulling a vacuum on the cooling system and letting it suck in coolant as well (my blue car didn't seem to have trouble bleeding air). Also tried massaging hoses.

I was kind of doubting the gauge, so I checked with the infrared gun. Water bridge is measuring about 205f when the gauge is still a bit below the orange. Radiator upper hose is around 185-190 and lower is about 175-180. Radiator gets hot, was measuring around 170 where I could get to it. I didn't have the balls to let it run much past that point though.

To me it seems odd that if I leave the cap on the expansion tank, the hoses never get firm. Hot, but not firm. With the cap off it doesn't seem like much expansion occurs either. Starting the motor does bring down the temp some if left to heat soak for a few minutes, so water is flowing. That said I am wondering in the back of my head about pump efficiency. The block did have some scoring from a previous impeller hitting it. I didn't think much of it at the time having only been 2 weeks into 928 ownership. The pump on it was fine though, so presumably it was working like that for a while.




So I do have a new temp sender on the way, but chances are it's not gonna tell me anything different. Anyone have any thoughts here where to look next? I'm gonna take my blue car out in a bit for a drive and plan to measure various parts of it's cooling system and see how they compare to the tan car.

[Crumpler]

What’s the fan situation?
Stock belt driven fan? Viscous Clutch in good working order?
I guess I would expect more of a drop in temp Between upper and lower radiator hoses, but the diagnostics you have done so far are what I would have done.
Something’s going on. It sounds like there’s air in the system still? Mine will do that after a coolant change and takes 1-2 heat cycles to burp everything out.

[worf]

To me it seems odd that if I leave the cap on the expansion tank, thehoses never get firm. Hot, but not firm. With the cap off it doesn't seem like much expansion occurs either.

You have a pressure leak. If there's no liquid coolant obviously leaking then the leak is in the vapor handling part of the system. This is every connection and component above the fill line on the reservoir including the reservoir itself.

The first culprit to check is always the cap. Buy/borrow/beg a cooling system pressure tester. Local 'big-box' parts store should have a tool loan program and should have cooling system pressure tester. Bring your cap with you to the store so as to get the right adapters.

So, get that and test the cap. A new cap should hold 12-14 PSI. Tired caps typically hold 7-ish PSI. Dead caps will hold more-or-less nothing. It's also possible that the rubber seal on the cap is not sealing.

If the cap holds 7+ PSI then hoses should get firm(-ish) if nothing else is leaking.

See directions I posted a couple of days ago on how to use the tester:

https://openroad.site/viewtopic.php?p=12639#p12639

If you see no liquid leaks using the tester and the cap is good (and one of your cylinders isn't filling with coolant), then you have to look for coolant vapor leaks:
- reservoir above fill level. (Usually where the fitting for the cap is bonded to the reservoir.)
- two small-hose connections to reservoir
- pressure switch (under washer filler neck and in-line with one of the hoses to the reservoir)
- water bridge connection
- radiator connection.

Find leak via spray bottle with soapy water, ear, and mark 1 eye ball, when the system is pressurized with the tester.

That said I am wondering in the back of my head about pump efficiency. The block did have some scoring from a previous impeller hitting it. I didn't think much of it at the time having only been 2 weeks into 928 ownership. The pump on it was fine though, so presumably it was working like that for a while.

One millimeter of volute surface damage will not decrease pumping efficiency. Three millimeters will decrease pumping efficiency.

If the temperature change is verifiably new behavior then look for leaks first before suspecting pump or volute surface.

[captainOCD]

Car just has the viscous fan. Seems like it's moving a lot of air. I have an anemometer so I could compare to my blue car.

I'll see about getting a pressure tester too. I know it's not as much force, but it does hold vacuum with the mighty vac. I can't verify for sure about the cooling performance. All I know for sure is there is some damage (doesn't seem very deep) but the water pump on it when I replaced it wasn't loose.

[captainOCD]

I ordered a pressure test kit, supposed to be here later this week.

Figured I'd check out how the cooling system on the blue car (which works great, never more than a needle above the 1st white line in normal zone, even in traffic with ac on) compares to what I saw with the tan car. Measured about 180-185 around the temp sensor. Upper hose on it is relatively firm. I couldn't reach the lower hose very easily (you know, spinning fan and hot motor), but it didn't feel as stiff as the upper hose. The upper hose was around 190 and the lower in the mid 170s.

So my observation there was that the blue car has the water bridge fairly close to the stat temp of 180 and the radiator inlet is about 10 degrees over the water bridge temp. That's the opposite of the tan car which is more than 20 degrees over the stat temp on the water bridge but only 185 ish inlet to the radiator.

[Majestic Moose]

You can use a broom against the spinning fan to see how much resistance there is. Having two similar cars is great because you can compare them.

[worf]

So my observation there was that the blue car has the water bridge fairly close to the stat temp of 180 and the radiator inlet is about 10 degrees over the water bridge temp. That's the opposite of the tan car which is more than 20 degrees over the stat temp on the water bridge but only 185 ish inlet to the radiator.

I've been pondering this and now realize that I'm not totally sure I understand your description.

Until the thermostat opens the lower radiator hose from the 'elbow' to the radiator outlet should be a *lot* cooler than the water bridge. The upper radiator hose to the inlet will be almost as hot as the water bridge.

Once the thermostat opens the lower hose temperature should go up considerably but should be somewhat lower than the water bridge.

So, the description of the tan 928 with the large temperature drop on the upper hose is strange.

Can the tan 928 be driven? It would be interesting to know if the engine temperature drops when cruising sedately at 50-65 mph on a not-too-hot day.

In any case, I might start with the high idle first. If you've got an intake leak you are probably running lean at idle and that's going to drive engine temperature up.

It's hard to tell from your picture but the volute surface damage from a previous metal impeller pump looks 'borderline' as in more than 1mm but not clearly 3mm or more.

Does the thermostat on the tan car open? Does the lower hose get hot(-ish)? You are sure the 'new' thermostat works and that you didn't put it in backwards or anything? (I did that once (was distracted due to conversation) but, caught it before I put the water bridge on.)

[captainOCD]

On the tan car the water bridge was about 205 around the temp sender, the radiator upper hose was about 15 degrees cooler at 190 degrees, and the lower radiator hose another 10 or so degrees cooler at 180 degrees. The car isn't currently road worthy or legal, so can't drive it. Most it's gone is 25 yards to the end of the street. It's also in the high 90s and quite humid here, hurricane season in SC.

I've tried 2 different thermostats in it. Both installed the correct way such that it seals off the bypass hole. One was a new motorad (drilled a bleed hole) and one a used wahler (with bleed hole up). Both opened around 180 in a pot of water on the stove. Whether or not they're opening in the car I don't know. I did get water when I took out the temp sender for the gauge (when cold of course), so I'm assuming that the thermostat is opening.

I haven't gotten the high idle figured out yet. The car has probably only ran for a total of 30-45 min in my possession. The first time running it for more than a couple seconds I was filling up the trans and suddenly the idle jumped from around 1k to 2k (not a great feeling when you're half under the car on ramps). It's been idling high since. Given it was sudden I was suspecting either a vacuum diaphragm let loose or the iac is acting funky. I tried spraying brake parts cleaner around the intake and couldn't get it to rev up. I previously hooked a smoke machine to the intake and didn't find anything obviously leaking then either.

I did forget to measure the fan speed between the two cars this weekend. Seems like it's moving a good bit of air though. Shroud is back on it.

Radiator pressure tester is supposed to arrive wednesday.

[SeanR]

I had an '87 that we were trying for months to find the coolant leak. Could not find anything under pressure when warm (which was every time he stopped by for me to look at it) and he said every time he came out to the garage in the morning it would leave a puddle. Finally had the car here over night and sure enough, there were drips coming off the AC compressor. Followed that drip line up to the water bridge and boom, there it was. One of a dozen reasons I'll never use a powder coated water bridge. Weeping from the sealing surface at the head. When it was warm it wasn't leaking and once started it would boil off from the engine heat so it was not apparent. Pulled the bridge, new gaskets (rubber and paper) with a good used bridge and no more leaks.

[captainOCD]

Hopefully if I do have a leak I can find it with the pressure tester coming tomorrow.

[captainOCD]

Well the pressure test kit did come. The only cap in the kit that will latch onto the coolant bottle has a stupid raised center section that prevents it from sealing (doesn't fit my charger either). Really don't know why they made that raised section. I was able to sort of rig it up to seal. Still seemed to be leaking a bit around my improvised seal, so can't tell if I have a small leak somewhere or not, but I certainly don't have a massive leak anywhere. I was able to get it to hold 10lbs for a bit.




I was able to test the cap (held 10 lbs).

[worf]

Well the pressure test kit did come. The only cap in the kit that will latch onto the coolant bottle has a stupid raised center section that prevents it from sealing (doesn't fit my charger either). Really don't know why they made that raised section.

This is kinda why I was hoping you'd get a loaner from Pep Boys (etc.) because those kits usually have 3 or 4 different caps and adapters for caps. It *might* be the case that the manufacturer of your kit offers an accessory that will adapt it to the "80s"-style European reservoir fitting.

I was able to sort of rig it up to seal. Still seemed to be leaking a bit around my improvised seal, so can't tell if I have a small leak somewhere or not, but I certainly don't have a massive leak anywhere. I was able to get it to hold 10lbs for a bit.

A small leak may take 10 minutes or more during a pressure test to make it's presence known as a puddle on the floor. A slow trickle can be really hard to notice until it hits the floor and then hard to trace back to a source.

And all you need is a small leak of either vapor or coolant to prevent the system from reaching operating pressure.

But, not keeping pressure will not cause the seemingly-bizarre temperature behavior you have noted. It will however make whatever other problem you have worse.

So... while you wait for the right adapter we need to figure out how you can diagnose the other problem(s).

You've still got a 'moody' idle and potentially some water flow problems. Right?

Do you have any idea of this 928's temperature behavior before you put a pump on it in 2018? What make of pump?

Did it idle OK before you did the work in 2018?

[captainOCD]

It appears that the 928 uses the same style of cap as my Charger and Durango, so I don't think it's an uncommon cap as much as the test cap for this size is just odd. I'm just gonna send it back since it doesn't fit 3 of the 4 vehicles I tried it on.


It seems like water is flowing, if I shut off the motor the temp goes up from heatsoaking. Starting it back up brings the temp back down some. Idle is still high between 1500 and 2k rpm.


I bought the tan 928 as a non runner (had been sitting for 10 - 15 years). Had no history either.

As far as the idle, I think I may need to see if I can get the the ISV and determine if it's causing the problem (unless there is something else worth checking first). The MAF and computers currently in this car both operate normally in my blue car. I wasn't able to find any vaccum leaks by spraying brake parts cleaner around.

[worf]

I bought the tan 928 as a non runner (had been sitting for 10 - 15 years). Had no history either.

As far as the idle, I think I may need to see if I can get the the ISV and determine if it's causing the problem (unless there is something else worth checking first). The MAF and computers currently in this car both operate normally in my blue car. I wasn't able to find any vaccum leaks by spraying brake parts cleaner around.

If you have the Moorehouse CDs, dig through them and find the LH/EZF troubleshooting guide. You can test the idle/wot switch, ISV, temp-II with a multi-meter. Beats guessing and wrenching.

[captainOCD]

All I have is the wsm

[Landseer]

20200905_014202.jpg

Buy CD set from roger. It includes wsm and so much more.

Here is a way to own a pressurizable cap pretty easily.

[Landseer]

CD set has the testing plan info referenced by Worf.

I tend to have been more empirical, trial and error. That was easier when take home pay was higher and 928 parts were very inexpensive back in 07 thru 11.

On this site now we are treated to advanced troubleshooting methodology, little clutter

So I'm reading very carefully the replies, trying to learn better ways.

I have had cooling problems with one car. One that Stan Shaw helped me rescue a few years ago. 32v car that sat least 10 years. There were 4 issues overlayed. Sediment in radiator. Hard to find leaks, hence the cap. Viscous fan that lost the silicon charge. And the biggest contributor by far, partially clogged injectors. Lean means hot. A smart guy said that above already, just wanted to emphasize it. Your lean condition may or may not, or may partially, be caused by something else. Hence test plan ref.

A red herring thrown into the mix of symptoms was persistent coating of oil inside plastic cooling reservoir. That cleared up over time. Played with my mind.

Another symptom was very white coating visible inside headers when disconnected from down pipes. That was lean showing itself.

Yours has a 5th possible contributor. Damaged volute. A very precise 928 guy just suggested, eyeballing a low res picture, it was borderline. At this point, I'd probably address everything else, then possibly revisit the volute if car, once sorted otherwise, still runs too hot. Only then, and there a couple ways to address that. Well, only one way for me. I burned that other bridge a few hours ago by insulting GB on another thread and he owns the repair kit.

[Majestic Moose]

I am using the OTC coolant pressure tester. It seals by inflating a bladder and works on the 928 and two other cars that I have tried. It is very adaptable.
https://www.otctools.com/products/cooli ... ure-tester

[captainOCD]

My new pressure tester came today and it does fit the car this time. After pumping up to 15psi I did find a small leak between the end tank and core of the radiator. It wasn't very fast though and seemed to fizzle out around 10psi. It certainly was not a fast leak.




Seems like that's still unlikely to be causing the hot running. When I changed the coolant I did put the water hose through the radiator. I suppose it's possible that part of the radiator is blocked (hard to tell with a fan on one side and ac condenser on the other). Beyond that I'm not sure what to think.

Figuring out the high idle is probably getting towards the top of the list too. I'd imagine there would be less heat when it isn't idling at 1800rpm.

[Eplebnista]

Just so I can avoid buying it, what pressure test kit did you buy that did not fit?

Thanks

[SeanR]

Just buy the generic Stant Coolant tester and it will work on your car. Only need to buy adapters if you have other makes that need to be played with.

[captainOCD]

I think it was this one from amazon. Looking at lots of those setups on amazon the caps look the same.

https://www.amazon.com/gp/product/B083Q ... UTF8&psc=1

I bought a different one on ebay that seals on the tank, but then the cheapo pump leaks where it connects to the cap. So yeah, get the stant one, I need to get one of those.



Guess I should update on that car. So I got busy with other projects for a while and haven't done much more with the car. I need to take the rad out and make sure it's not full of crud then go from there. Probably need to get the high idle figured out too, idling at 2 grand and possibly with a bad mixture isn't helping.

[worf]

Seems like that's still unlikely to be causing the hot running.

Not being able to keep the system pressurized was never going to be the *cause* of the issue. Sorry if I left you with that impression.

Not being able to keep the system pressurized *will* lower the boiling point of the system. So, you have less margin available and thus the overheating problem is more of a problem.

This BTW, is the kit I have:

https://www.amazon.com/Astro-78585-Univ ... =hi&sr=1-2

Yeah, all of the caps except one are useless for 928 stuff. But, the vacuum pump. hand pump, and the adapters are useful.

[SeanR]

This is the one I have. Works great and then I found myself needing adapters for the other cars that come in, so I have $400.00 in adapters and one of those kits you guys have posted most likely would have worked better the first time.

https://www.amazon.com/Stant-12270-Cool ... 197&sr=8-3