Ht 4100 Question

[Andrew Garnett]

1985 HT 4100 thermostat keeps clogging, can I drive car without it?

[Rusty Shepherd CLC 6397]

Ive read that removing the thermostat in flathead Ford V-8s can cause those engines to run even hotter than they usually do because the water flows too quickly to effectively absorb and remove engine heat, but I dont think that applies to most other engines. Probably the only major downside would be a longer time before you get heat inside the car on a cold day. If it were mine, Id be wondering (and concerned)about the repeatedly clogged thermostats. Two thoughts enter my mind: 1. Whats causing it (maybe too much coolant supplement aka HT4100 stop leak)? and 2. If the thermostats are clogging up, most likely the entire cooling system (including block passages) is, too, which will sooner or later result in engine overheating (something that is really to be avoided in aluminum engines, and the HT4100 in particular).

[Brian Rachlin]

DO NOT USE A POWER FLUSH, BACK-FLUSH, OR ANY FLUSHING ADDITIVES!!

You need to gently flush the system until you see clear water coming out of the open petcock from the radiator, and the top of the radiator.

It will be time consuming, but try this:

1.  Drain out the coolant from the radiator and discard safely.
2.  take out the clogged thermostat.  Leave it out for now, and put the housing back on.
3.  Fill with water, run with heater on high until heater hoses become warm, showing flow through the core.
4.  Dump coolant again, and refill with water.
5.  Run it until warm again, open petcock at radiator and leave radiator cap off.  Trickle hose into top of radiator to keep up with loss from radiator petcock.
6.  When only clear water is running out the bottom, turn off engine, let it all drain out.
PUT IN A NEW THERMOSTAT AND NEW GASKET.
7.  Use the GM coolant suppliment tablets, crush up all 6 pills, and add the powder slowly while filling the first gallon of antifreeze.  Mix the 2nd gallon 50/50 with water, and add that in.  Start it up, finish filling the radiator, put the cap on and drive with the heat on for 20 minutes.
You will have circulated the coolant and the suppliment sufficiently.  Let the car cool completely and check coolant level again.

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The HT4100 engines have sealing problems with respect to the intake manifold, head gaskets, and block porosity.  If you power flush it, you could dislodge a piece of a gasket or some of the collected collant additive that has been sealing up a problem area for years.  Same reasoning on not using a flushing compound.

You walk a fine line between clogging the system, and sealing the system, but following the above proceedure should keep you out of trouble.  I would strongl recomment signing up for the message forum at http://www.ht4100.com TARGET=_blank>www.ht4100.com to keep in contact with fellow 4100 owners.  Misery does love company.

Good luck...

Brian

PS...The best thing to do if your radiator looks like it is all scaly and cruddy inside is to buy a brand new radiator.  Your coolant will flow better, and the fresh radiator will drop your operating temp by about 10 degrees, which could really save your engine.

[George Woodford clc21025]

Last year I changed the antifreeze in my 83 SDV HT4100 masterpiece.  I just drained it, refilled with water, and drained it again.  I repeated the process a few times before refilling it with antifreeze and additing the tablets.  I havent had any problem with the thermostat after 71K miles.  Using a flush might weaken the seal of the gasket.  As stated, you might want to service the radiator or even replace it.  There might be some debris that continues to break apart from the cells in the radiator that clogs the thermostat.

[Andrew Garnett]

any experience with installing a radiator filter to prevent debris build up in the radiator?

Andrew

[George Woodford clc21025]

No.  You might want to take it to a radiator shop and have it cleaned or just replace it.  I had my radiator cleaned at 30K and it wasnt in that bad of condition.  It is probably easier and cheaper to buy a new one (aftermarket) and replace your old one.  Remember an HT4100 will fail in 90 seconds, if it overheats.

[Mike #19861]

 Back to your original problem and question.

 No, it is not adviseable to drive any car without the thermostsat, particularly fuel injected cars. The engine will never reach operating temperature. This will cause the engine to run rich and emission levels to be high. Obviously fuel economy will be affected as well. It is also possible that the system will never attain closed loop status which will lead to further driveability issues. In short, use the recommended 195 degree thermostat.

 Now, is the thermostsat actually clogging, or is it failing to open. I have never heard of a thermostsat clogging. If this is so, then the rad and heater core will be completely plugged as well. You will have other issues to deal with here if this is the case.

 Quality of thermostats can vary by quite a bit. Many aftermarker thermostats can fail after only a short time. I would recommend using a proper GM scourced thermostat for your engine.

 I would determine if the engine is actually overheating. These engines (or any aluminum engine) do not take well to overheating. You can access many of the engines operating parameters through the ECC display. You can find out the process in the shop manual or at http://www.ht4100.com TARGET=_blank>www.HT4100.com

 The HT4100 certainly has its issues. The main cause for failures is coolant intrusion into the oil through either the head gasket sealing surface or the intake gasket. This is combined with poor maintenance, ie extended oil change intervals and failure to replace the coolant on a bi-annual basis with the addition of the pellets. This is imperative for the long term survival of these engines.

 Now, many early HT4100s failed because of lack of maintenance and cylinder head migration causing the head gaskets to leech coolant into the oil. This was fixed with the addition of solid cylinder head dowels and impacted graphite head gasket materials. If the engines were properly maintained from the get go, failures were not much of an issue. Many of these cars were not maintained initially, but subsequent owners may have embarked on a good maintenance program, but the damage had already been done.

 Also, block porosity was never a real issue, contrary to what has been said here in the past. The process of die casting inherantly produces some porosity, but the porosity is never linked to allow a path through the casting in any appreciable amount. The blocks were never changed from the initial design right to the end of the 4.9 engines, except for the addition on some ribbing on the later 4.5 and all 4.9 blocks. They used the original dies, but just added the ribbing for increased strength for the higher power levels of the port injected 4.5s and 4.9s. The reason for using the pellets is to ensure that no coolant migration throgh the block can occur in any amount (which it can in small amounts over time), as well as offer additional protection against any internal or external leaks.

 Also, Mercury Marine never had anything to do with the improved 4.5s. This was done in house, and was a culmination of the updates of previous 4100s. No new procedures or processes were employed specifically for the 4.5s.

 So, early HT4100s can fail, this due to the fact that the cylinder heads can migrate causing head gasket leakage. This can happen in small amounts over time in which the coolant can have adverse affects to camshaft and bearing wear patterns. Regular oil changes can largely prevent this process. Head gaskets can also fail allowing coolant into the oil and creating the mushroom soup that we all dread. But, most of the time this happens to the oil, its a result of intake manifold gasket failure. If this happens, you MUST use the updated GM gasket kit that has the impacted graphite gaskets, and spring washer bolts part #3834742.

 The type of oil you use can also have an affect on the long term durability of the engine. I would recommend any of the HD deisel 15W40 oils such as Rotella T, Delo or Delvac oils. They have a higher detergent level and incresed ZDF levels that combat wear. If the engine has been subjected to any longer drain intervals it would be wise to add a can of GM EOS to the mix. This containes a high content of ZDF which can actually heal minor engine damage that has aoccured from coolant intrusion casued galling. Synthetic oils offer no advantages.

 The HT4100 has a reputation, but much of it is not deserved. Many of the early problems were a result of the gas and go mentality of the average motorist. There are still many early HT4100s out there in good condition. This is simply beacuse they were maintained properly from the get go.

  Mike

[Porter 21919]

Mike,

You went way out of your way sharing that information here about the HT 4100 engines.

Although they are not durable engines like the cast iron blocks of yesteryear that could take much abuse with poor maintainence they were the forerunner for todays aluminum block engines, which arent much better anyway, perhaps cast iron engine blocks will be relegated to the dustbin of history.

As you have stated, with proper maintainence they will hold up well and were initially offered to provide good gas mileage.

Im sure many of the other foreign car engines were no better at the time.

Nothing beats a good old cast iron SBC though.

Porter

[Mike #19861]

 Yes, these really were the forerunner of many of todays aluminum block engines. They pioneered certain testing techniques as well. In order to test gasket durability, they were subjected to extreme temperature cycling. In this, the engine was run hot, then immediately flushed with cold coolant, then run hot and done again. The HT4100 and later versions, were tested to 300 of these cycles. That test was developed specifically for the HT4100. Current engines now use this test for 1200 cycles!

 I doubt we will ever see all cast iron engines in our cars again. They are simply too heavy, and with the developments of the aluminum engines, which the HT4100 pioneered, they have become even more durable than any of the old cast iron engines, but maintenance has become more critical.

 You could really abuse some of these old engines, but with continued abuse and neglect, it had a very adverse affect on the life of the engine. They perhaps could go longer being abused than some of the new generation engines, but it still really shortened their lives.

 I have torn into many engines that have needed major repairs long before their time. Most always it was the result of poor maintenance. Even the venerable SBC was not immune to this.

 Also, oils have really progressed in the last 10 to 20 years. They can protect an engine longer than the oils we knew in the 70s and 80s.

  Mike