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View Full Version : Long cranking time when hot... Isn't that backwards?


Jason
09-10-2009, 06:00 PM
Since I have been daily driving the volvo for the past few days (finnally got it licensed) it cranks for quite a while when hot before it starts. If you shut it off and go to restart in within a few seconds, it fires right up. If you go inside someplace, or it sits for a half hour or better, it cranks for a long time. The engine is still warm, and I'm not getting any glow plug light. My experience has always been that these engines start more easily when hot if they are low on compression, and have a hard time starting when cold. My car starts instantly when cold, with no excessive smoke or stress. I was wondering if the problem was related to having the pump turned up, since its pushing more fuel. I tried pressing the accelerator down part way and that made it crank longer it seems, so I'm thinking too much fuel is the problem. My turbo diesel jetta had the pump cranked and I never had any hot start issues. I'm sure if I wired up a jumper switch to be able to run the glow plugs for a few seconds it would start, but I shouldn't have to do that with the engine hot.

Thanks for any suggestions.

Jason

v8volvo
09-10-2009, 06:28 PM
It's just got low compression. On VWs, even though the glow plug light doesn't come on with the engine warm, the plugs still get turned on and are on while cranking, so VWs don't have this issue when their engines start to get worn out. Volvo's glow system doesn't activate the plugs at all if the engine is above a certain temp threshold, so it can crank for quite a while when the engine is just warm enough that the plugs aren't operating but it has been sitting for awhile.

That is often what sends these cars to their grave -- won't start when warm due to worn bores. A few days ago I paid $35 for a pristine 1985 744 TD... you guessed it, it starts when cold but if you turn it off once it warms up and let it sit for half an hour it won't start at all. It was ready to go to the junkyard until I snagged it.

If your engine runs OK otherwise, I'd just install a pushbutton switch so you can turn the plugs on when you want to. You can run it alongside the factory relay system using a Ford starter solenoid. Pain in the ass but that's how it goes with these engines.

Jason
09-10-2009, 06:39 PM
I'm not sure the early jetta glow systems were that way.. The TDI glow plug system may glow even when hot. It didn't do it before I started messing with the pump... I haven't checked the compression but I'm pretty sure its up there. It starts really well when cold, no extra cranking at all. I thought even with the glow plugs low compression engines started hard when cold.

Jason

v8volvo
09-10-2009, 07:05 PM
Check out an older VW and you'll see that that's how they work. IDI diesels really need glow to start even when they are somewhat warm so I can see how even a pretty sound D24T might crank for a longer period of time under certain circumstances, given the design of the Volvo system... but it shouldn't be too long.

An IDI diesel with good glow plugs and a good battery will start from cold even if it has very low compression. Witness my '85 744, which will not start *at all* when lukewarm unless you manually power up the glowplugs, but starts perfectly from cold every time. I had an old Rabbit with almost no compression until I rebuilt it. That also started perfectly from cold with good glow plugs, even though it went through a quart of oil every 100 miles!

A TDI won't use the glow plugs at all until the temp gets down below about 47F. Check it out with a test light next time you work on a TDI (at least an older one, up to 2003 or so) and you'll see this is true. Direct injected diesels are a completely different animal. They will start under most conditions without any glow, period. You can disconnect the plugs on a TDI and it will still start even if it's below freezing out (yeah it will be smoky and rough, but it will start). IDI diesels are the opposite -- they NEED the plugs when cold or they won't even try to start, and as you found out, they sometimes need em when warm too.

The difference has to do with the ratio of combustion chamber surface area to volume, which is much higher on an IDI than a DI, resulting in much more heat loss to the surrounding metal parts (cyl head, prechamber, piston, etc). That's the same reason why a direct injected diesel has higher efficiency than an IDI one, if all other factors are kept constant, and why the manufacturers were able to make the glow time so much shorter on diesel engines once they switched to DI.

Jason
09-10-2009, 07:43 PM
I had a 85 turbo diesel, and when I redid the car the glow system was shot (wires were hacked,) untill I had a chance to make a new harness. I had a makeshift jumper setup so I could light them when cold, but never used it/needed it when hot. Only reason I mentioned the TDI was my 99 always had the glow light on come on even when hot, though it was very very short.

I think the extra fuel has made it worse, but thats just life I suppose. Its not like it takes so long your wondering if its going to start, but compaired to how it starts when cold its a good bit longer. I'm thinking about doing a relay off the starter signal wire, so they will just glow when I crank it. It doesn't really need much, and that would keep me from having to install another switch somewhere in the dash...

I'm going to bring home a compression tester tomorrow and check it, I'll post up what I find.

Jason

MRDART
09-11-2009, 07:30 AM
There is a temp sensor on the back of the cyl head... if you take the wire off you will get the glow cycle everytime you turn the key...

Jason
09-11-2009, 10:20 AM
Won't that make it glow for the longest time possible? It would always think its 20 below outside. I would think that would kill the glow plugs quite a bit sooner.

Jason

v8volvo
09-11-2009, 04:36 PM
Yeah, that will be a lot more glow than you need under any circumstances. If it were me I would just put in a momentary switch and relay alongside the stock system. Running the plugs only when cranking will help but might not be enough glow to make it start the way you want it to. Running the plugs for a few secs before hitting the starter will make it light off immediately.

TDIs light up every light on the dash for a split second when you first turn the key on, so the GP light illuminates briefly regardless of whether the engine is hot or cold. However, the actual plugs will only get power when the engine is cold, or if they do get power when warm, it will only be for a split second. It doesn't need em in order to start.

Sounds like your engine is fairly normal. My '85 740 and '83 760 with D24Ts in reasonably good shape also will both crank a little longer when warm than when cold, especially if they have been sitting for a half hour or so. I wouldn't worry about it... or if you find it bothers you, just rig something up to light the glowplugs briefly.

Let us know what you find on the compression test.

v8volvo
09-11-2009, 09:28 PM
It is possible that turning up the fuel has made things worse, since excessive soot can crud up the rings and make them not seal as well. If you are getting a lot of black smoke, you might want to turn the fuel down and clean it up a bit. The soot doesn't give you any additional power, and the extra particulate matter inside the cylinders makes rings and bores wear out faster.

Jason
09-12-2009, 04:12 AM
Very true, though I was thinking more along the lines of it having a harder time igniting the extra fuel its getting. I've only been daily driving it for a few days, and I've only put about 500 miles on the car since I got it. I would expect it would take a while to coke the rings up that bad. I know that was a problem with the NA engines, but mine cruises nice and clean. I blow some smoke now and then, but its not chugging black all the time...

Jason

m-reg
09-12-2009, 09:00 AM
could be faulty glow relay I got a book for early 760 D which says the plugs are live when cranking and for up to 14 secs after dep on temp so every thing Ive seen says it should glow when cranking whatever the temp (the light dont come on though) try the hot wire method and you"ll soon see if its the plugs or not. even the current volvo 24d does it and has afterglow despite its multi valve digital wizardry twin turbo vnt etc etc greenbook list for poor hot start reads pump sucking air, fuel leak, timing, fuel filter blocked, glow relay, compresions, and valve clearances etc covers most of it really hope that gives afew ideas yeh the glow light only comes on in the pre heat phase, not when cranking or after glow. just remembered