another run hot post . . . runs hot on Highway

**Duke W.** · February 28, 2004, 12:41 PM

Re: another run hot post . . . runs hot on Highway

"Timing/Dwell set to specs, all seems to be well there"

You need to check the entire ignition map - vacuum and centrifugal advance.

Setting initial timing on 64/65 SHP/FI engines is VERY TRICKY!!! The centrifugal starts at about 700 so you have to reduce revs below this to set the initial (vacuum can disonnected), which means the engine is just barely running and may even stall before you can complete the job.

The best way to set timing on these engines is to set the total initial plus centrifugal at 2500 to 3000 (the centrifugal is all in at 2350) with a dial back light to 36 +/- 2 degrees.

What is the number on the vacuum can? It should provide 16*@8", which means it should be pulled to the stop at 900/10" idle conditions. If you check total idle timing (vacuum can connected) it should be in the range of 28-34 degrees.

Duke

**Brad K.** · February 28, 2004, 12:46 PM

another run hot post......runs hot on highway

Jack,
This embarassing to tell, but I solved a "mysterious" overheating problem a few years ago after I discovered, after I removed the bolt-on plate on the back side of my water pump, that I left a shop towel stuffed inside the radiator hose inlet to the pump. I stuffed it inside the hole to prevent dripping on the floor. It was inside to far and I forgot about it. I hooked up the radiator hose put it all back together and the rag wrapped itself around the impellor and lo and behold...I had a problem that took me a week to troubleshoot!
This may not be your problem, but it may be worth a look!
Brad
#18060

**Jack W.** · February 28, 2004, 01:03 PM

Re: another run hot post . . . runs hot on Highway

dwell set then timing set to specs using a dial back timing light, all in at 36, vac can brandy new correct Echlins mod for the SHP, Duke I am a student of your advice and have taken it on this engine - but out of curiousity, is incorrect timing a likely issue when one experiences hot at highway speeds only? I will certainly double check the timing again . . ..

**Jack W.** · February 28, 2004, 01:07 PM

Re: another run hot post......runs hot on highway

Brad, thanks for sharing an embarassing story of your own - I could fill a page here with some of my bright moves! I have this nagging feeling that I might have some sort of blockage problem (don't think I put a rag in my pump before the install, but I have a w-pump gasket laying around, I might pull the thing off to see whatI can see there.) I guess I could use some advice if a blockage of sorts would really manifest at highway sopeeds only . . . .

**Joe C.** · February 28, 2004, 02:16 PM

Re: another run hot post . . . runs hot on Highway

Jack:

Your cent advance should be all in at 2350 RPM. I don't think that that is your problem, though.
A couple other things to check, but probably not an issue, but it can't hurt:

1. Be sure that the heat riser is working properly.
2. Be sure that your valve lash is set correctly.

One thing to check, that is very important for your engine at speed. Make sure that you do not have excessive gaps between your shroud and radiator. Too many large gaps will permit some air to bypass the rad.

What is the actual IR reading at the base of the temp sender? And what is the gauge reading at that point. These engines will normally run slightly hotter "at speed", and as you know, the temp gauge is not linear. Any slight increase in actual temp will be exaggerated by the gauge.

Joe

**William V.** · February 28, 2004, 05:38 PM

Re: another run hot post......runs hot on highway

Jack

I'm sure this has been checked. However, your thermostat may not be fully opening. Suggest you remove it and check it in a pot of hot water and a meat thermometer.

If you are reomving your waterpump you should also remove the backing plate and check the condition of the impeller.

I had an overheating problem that was driving me nuts with a marine diesel. The hose that connected the raw water pump to the engine was collapsing on the inside and blocking the flow. on the outside it looked and felt fine. The engine temp and flow was fine until I ran it up to speed then the water stopped flowing out the exhaust and it over heated until I brought it back to idle. the increased flow caused the lip inside the hose to flip back and block the flow. When the engine slowed down the flow pressure decreased and water started to move. I replace a $400 dollar water pump before I found the problem The replacement hose cost $10. You said you checked an replace hoses. however it's worth the thought.

**Duke W.** · February 28, 2004, 05:59 PM

Re: another run hot post . . . runs hot on Highway

Vacuum advance issues often cause hot running/overheating at idle and vacuum advance or centrifugal advance issues can cause overheating at cruise.

Just wanted to make sure that you had properly checked out the entire ignition map.

If the timing map is okay, overheating a speed makes the radiator suspect, but with a new DeWitts that's probably not on the table, so I'm at a loss.

Love the rag in the impeller story - one of the best I've heard in awhile.

Duke

**Jack W.** · February 28, 2004, 06:00 PM

Re: another run hot post . . . runs hot on Highway

heat riser eliminated, FI heat riser elimiantor spec piece on there now, I should have mentioned that in my intial post. Valve lash huh? Guess I'll have to dig out Duke's solid lifter valve spec & adjustment paper! As for the off-age of the temp gauge, interesting point about the thing not being linear. Previous handi-work witht he IR gun told me that indicated 180 was 190; 210 (or whatever that hash mark between 180 and 240 represents) is really about 195; proves your point.

The fact that it it is fine at idle but problematic when cruising (where the tach is showing 2000 or more) would sure seem to have been a collapsing lower rad hose thing, but I pulled a newly installed hose and replaced it with another (both having perfectly intact inner springs) just to eliminate that issue. Strange thing is, within seconds of clutch in coasting the temp guage settles back down . . .

**Jack W.** · February 28, 2004, 06:02 PM

Re: another run hot post . . . runs hot on Highway

rrr, no ability to edit - I flipped the indicated and actual temps in my previous post - when the gauge said 190 it was really 180

**Les Jacobs** · February 28, 2004, 08:26 PM

Re: another run hot post . . . runs hot on Highway

Jack My "overheating" was due to a grossly out of whack temp gauge which read hot at low speed, warm day. What threw me off was that the gauge read 180 at cruising speed, so I didn't initially suspect the temp circuit. In fact the thermostat had been removed and it was actually 160 at cruising speed. So, when it was really 190 it was reading 220. It is curious that yours cools so quickly. Wonder if there's a possible connection to the charging circuit. (Higher voltage and temp reading @ highway speed, lower voltage and temp when idling?) What is the IR temp when your gauge is reading HOT? Les

**Joe C.** · February 28, 2004, 09:32 PM

The Proof Of The Pudding

It is very refreshing to talk to somebody who actually takes the time to absorb, and respond directly to the advice being given.

It is my experience, that the cooling system of these cars, DeWitt's, or original Harrison radiator notwithstanding, is operating at the ragged edge of the design limit. There is almost no margin built in. Ever wonder why there are so many "overheating" complaints, many of which remain unresolved? Do you remember the traffic jams of old, where scores of cars were seen at the side of the road, with steam gushing out from under the hood? Remember when, in the summertime, we had to keep one eye on the temp gauge, when caught in traffic? Remember trying all sorts of remedies to attempt to keep the temp down? (i.e. "turn on the heater full blast", "throw 'er in neutral" to uncouple the automatic trans, and unload the torque converter, etc, etc. We don't see very much of that anymore, and so most of us now take our cooling systems for granted.

All of that being said. In order to optimize your cooling capacity, please do the following:

1. Check your valve lash.
2. Make sure that your centrifugal is all in @ 2350 RPM.
3. Eliminate any excessive gaps between the rad and the shroud.
4. If the engine is even SLIGHTLY tight from a recent rebuild, it WILL run hotter for awhile.

Now, the proof. If you are running 50/50 coolant, and a 15 psi cap, then you can safely run at a measured (shoot the IR at the base of the temp sender)intake mainfold temp. of NO MORE than about 245 degrees. If the engine does not actually boil over, then I would not worry about it.

Joe

**Jack W.** · February 29, 2004, 04:37 PM

Re: another run hot post . . . runs hot on Highway

ok Duke, (insert sheepish look here) I took advantage of the beautiful day here in the Northeast to double-check my timing, I always start with the things I swear to God are done right already (perhaps the story about the rag in the water pump inspired me?) and guess what? Using the dial-back timing light (I agree Duke, the only way to really get it right on my SHP L76) the darn thing was 4 degrees off of 0 up at 2500 while dialed up to 36! (Fire that man who set the timing earlier! Oh wait, that was me). But I would swear I had done this drill faithfully just a few weeks ago when I reinstalled the distributor, maybe I twisted it a bit when I cinched it down after setting the timing . . . by the way, am I the only one that finds that distributor hold down bolt a real PITA to get a wrench on and make headway? I put a 30 deg. bend in an extra 9/16 wrench on purpose just to make it easier . . .

Car still runs hot (but now only about 210 - 215, so it has come down a little) up at cruising speed, and actually runs an indicated 180 even at long-term idle (which is really like 170-ish per my IR gun). All of this on a 55 degree day, of course, and that's my fear - if I cannot keep it together now, I know what the summer will bring. That ok idle / hot at cruise still irks me, in all my life I have never had a car run hot at cruise and cooler just idling away. I will check the valve adjustment some day soon Joe, I have never checked it since getting this car a year ago and I should not assume all is well there, even if the thing was "rebuilt" 5,000 miles ago by Mr. no-longer-in-operation Vette "specialist" shop while under previous ownership. I also will pull the water pump and have a looksee, an easy possible issue to look into.

Thanks everyone for the good suggestions.

**Duke W.** · February 29, 2004, 07:21 PM

Re: another run hot post . . . runs hot on Highway

Four degrees as you found will not make a big difference.

Check the total idle timing and total cruise timing with the dial back light. With the vacuum can hooked up you should see about 30 degrees at idle and about 52 degrees at 2500-3000 free revving with no load. This test takes less than a minute and will tell you if the vacuum can is operating properly. The specs are 0@4" and 16@8", so at idle and revving with no load the 16 degrees should be locked in.

Total idle timing is initial plus full vacuum, plus a couple of degrees centrigal since it starts at about 700. Total cruise timing is initial plus full centrifugal plus full vacuum, which you should see at over 2350 since this is the specified speed for full centrifugal for your engine.

Duke

**Mike M.** · March 1, 2004, 02:23 PM

Re: another run hot post......runs hot on highway

Strange but true. While in college was challanged to "fix" a '66 GTO that overheated at highway speeds (389/360, 4sp, TI). This was in 1969. Car had suffered a minor front end collision over the summer and overheating started after being repaired. New radiator, hoses, fan, shroud, etc. Dealer even installed new 180 thermostat. Never got the car right, owner drove it from Baltimore to Blackburg at 45 mph. I checked all the usual including timing and that correct parts had been used to replace originals. To cut to the chase, the water pump impeller was slipping on the shaft. Did not slip forward or backward enough to tell. Finally traced it by marking shaft/impeller and removing to check position afterwards (broke college students don't just buy replacement pumps, gaskets are cheaper). Took the pump to the ME lab and checked in water bath. Sure enough, at 170 degrees the impeller was loose. Replaced the pump and the problem went away forever. Want a good bubba story? Same car lost timing gear about two months later. I was away on an interview trip. Got back and Bubba told me the the car wouldn't run because the "distributor done blew up, couldn't even find the points!"

another run hot post . . . runs hot on Highway

another run hot post . . . runs hot on Highway

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